Patent Publication Number: US-2019167147-A1

Title: Injection-less methods to determine-cross-sectional areas using multiple frequencies

Description:
PRIORITY 
     The present application is related to, and claims the priority benefit of, U.S. Provisional Patent Application Ser. No. 62/371,045, filed Aug. 4, 2016, the contents of the contents of which are hereby incorporated into the present disclosure by reference in their entirety. 
     RELATED APPLICATIONS 
     The present application is related to U.S. patent application Ser. No. 13/520,944, filed Jul. 6, 2012, the contents of which are hereby incorporated into the present disclosure by reference in their entirety. 
    
    
     BACKGROUND 
     Coronary heart disease (CHD) is commonly caused by atherosclerotic narrowing of the coronary arteries and is likely to produce angina pectoris, heart attacks or a combination. CHD caused 466,101 deaths in the USA in 1997 and is one of the leading causes of death in America today. To address CHD, intra-coronary stents have been used in large percentages of CHD patients. Stents increase the minimal coronary lumen diameter to a greater degree than percutaneous transluminal coronary angioplasty (PTCA) alone. 
     Intravascular ultrasound is a method of choice to determine the true diameter of a diseased vessel in order to size the stent correctly. The tomographic orientation of ultrasound enables visualization of the full 360° circumference of the vessel wall and permits direct measurements of lumen dimensions, including minimal and maximal diameter and cross-sectional area. Information from ultrasound is combined with that obtained by angiography. Because of the latticed characteristics of stents, radiographic contrast material can surround the stent, producing an angiographic appearance of a large lumen, even when the stent struts are not in full contact with the vessel wall. A large observational ultrasound study after angio-graphically guided stent deployment revealed an average residual plaque area of 51% in a comparison of minimal stent diameter with reference segment diameter, and incomplete wall apposition was frequently observed. In this cohort, additional balloon inflations resulted in a final average residual plaque area of 34%, even though the final angiographic percent stenosis was negative (20.7%). Those investigators used ultrasound to guide deployment. However, using intravascular ultrasound as mentioned above requires a first step of advancement of an ultrasound catheter and then withdrawal of the ultrasound catheter before coronary angioplasty thereby adding additional time to the stent procedure. Furthermore, it requires an ultrasound machine. This adds significant cost and time and more risk to the procedure. 
     One common type of coronary artery disease is atherosclerosis, which is a systemic inflammatory disease of the vessel wall that affects multiple arterial beds, such as aorta, carotid and peripheral arteries, and causes multiple coronary artery lesions and plaques. Atherosclerotic plaques typically include connective tissue, extracellular matrix (including collagen, proteoglycans, and fibronectin elastic fibers), lipid (crystalline cholesterol, cholesterol esters and phospholipids), and cells such as monocyte-derived macrophages, T lymphocytes, and smooth muscles cells. A wide range of plaques occurs pathologically with varying composition of these components. 
     A process called “positive remodeling” occurs early on during the development of atherosclerosis in coronary artery disease (CAD) where the lumen cross-sectional area (CSA) stays relatively normal because of the expansion of external elastic membrane and the enlargement of the outer CSA. However, as CAD progresses, there is no further increase in the external diameter of the external elastic membrane. Instead, the plaque begins to impinge into the lumen and decreases the lumen CSA in a process called “negative remodeling”. 
     Evidence shows that that a non-significant coronary atherosclerotic plaque (typically &lt;50% stenosis) can rupture and produce myocardial infarct even before it produces significant lumen narrowing if the plaque has a particular composition. For example, a plaque with a high concentration of lipid and a thin fibrous cap may be easily sheared or ruptured and is referred to as a “vulnerable” plaque. In contrast, “white” plaques are less likely to rupture because the increased fibrous content over the lipid core provides stability (“stable” plaque). A large lipid core (typically &gt;40%) rich in cholesterol is at a high risk for rupture and is considered a “vulnerable” plaque. In summary, plaque composition appears to determine the risk of acute coronary syndrome more so than the standard degree of stenosis because a higher lipid core is a basic characteristic of a higher risk plaque. 
     Conventionally, angiography has been used to visualize and characterize atherosclerotic plaque in coronary arteries. Because of the recent finding that plaque composition, rather than severity of stenosis, determines the risk for acute coronary syndromes, newer imaging modalities are required to distinguish between and determine the composition of “stable” and “vulnerable” plaques. Although a number of invasive and noninvasive imaging techniques are available to assess atherosclerotic vessels, most of the standard techniques identify luminal diameter, stenosis, wall thickness and plaque volume. To date, there is no standard method that can characterize plaque composition (e.g., lipid, fibrous, calcium, or thrombus) and therefore there is no routine and reliable method to identify the higher risk plaques. 
     Noninvasive techniques for evaluation of plaque composition include magnetic resonance imaging (MRI). However, MRI lacks the sufficient spatial resolution for characterization of the atherosclerotic lesion in the coronary vessel. Minimally invasive techniques for evaluation of plaque composition include intravascular ultrasound (IVUS), optical coherence tomography (OCT), raman and infrared spectroscopy. Thermography is also a catheter-based technique used to detect the vulnerable plaques on the basis of temperature difference caused by the inflammation in the plaque. Using the various catheter-based techniques requires a first step of advancement of an IVUS, OCT, or thermography catheter and then withdrawal of the catheter before coronary angioplasty thereby adding additional time and steps to the stent procedure. Furthermore, these devices require expensive machinery and parts to operate. This adds significant cost and time and more risk to the procedure. 
     Thus, a need exists in the art for an alternative to the conventional methods of determining cross-sectional area of a luminal organ and determining the plaque-type of a plaque present within a luminal organ. A further need exist for a reliable, accurate and minimally invasive system or technique of determining the same. 
     BRIEF SUMMARY 
     The present disclosure includes disclosure of a methodology for determining a cross-sectional area of a luminal organ using an impedance device without requiring any fluid injections in connection with the same, as described herein. 
     The present disclosure includes disclosure of a methodology for determining a cross-sectional area of a luminal organ using an impedance device without requiring any fluid injections in connection with the same by introducing three different frequencies through the impedance device, as described herein. 
     The present disclosure includes disclosure of a method, comprising the steps of introducing at least part of an impedance device into a luminal organ so that a detector of the impedance device is positioned within the luminal organ; introducing a first frequency through the detector of the device and obtaining a first conductance measurement using the detector in connection with the first frequency; introducing a second frequency through the detector of the device and obtaining a second conductance measurement using the detector in connection with the second frequency; introducing a third frequency through the detector of the device and obtaining a third conductance measurement using the detector in connection with the third frequency; and determining a cross-sectional area of the luminal organ using the first conductance measurement, the second conductance measurement, the third conductance measurement, and the conductivity of fluid within the luminal organ, such as blood, and a known distance between detection elements of the detector. The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the luminal organ using the determined cross-sectional area at the first location and at least one additional cross-sectional area obtained by performing the steps of the method at a second location within the luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of fluid within the luminal organ is determined by operating the detector of the device within a catheter positioned within the luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the step of introducing at least part of the impedance device is performed to position the at least part of the device into the luminal organ wherein the detector comprises the two detection electrodes positioned in between two excitation electrodes, wherein the known distance between the two detection electrodes is at least 0.5 mm The present disclosure includes disclosure of a method, wherein the steps of introducing the first frequency, introducing the second frequency, and introducing the third frequency are performed by operating a frequency generator in communication with the device, the frequency generator selected from the group consisting of an arbitrary waveform generator and multiple signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, wherein the first location comprises a plaque site, and wherein the determining step is further performed to determine a plaque-type composition of a plaque at the plaque site. The present disclosure includes disclosure of a method, wherein the step of introducing at least part of the impedance device is performed by introducing at least part of the device into the luminal organ selected from the group consisting of a body lumen, a body vessel, a blood vessel, a biliary tract, a urethra, and an esophagus. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. 
     The present disclosure includes disclosure of a method, comprising the steps of percutaneously introducing at least part of a device into a mammalian luminal organ; operating an impedance detector of the device to obtain first conductance data while a first signal of a first frequency is introduced into the mammalian luminal organ by the device; operating the impedance detector of the device to obtain second conductance data while a second signal of a second frequency is introduced into the mammalian luminal organ by the device; operating the impedance detector of the device to obtain third conductance data while a third signal of a third frequency is introduced into the mammalian luminal organ by the device; and determining a cross-sectional area of the mammalian luminal organ based upon the first conductance data, the second conductance data, the third conductance data, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of the impedance detector. The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the mammalian luminal organ using the determined cross-sectional area and at least one additional cross-sectional area obtained by performing the steps of the method at a different location within the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of blood within the mammalian luminal organ is determined by operating the impedance detector of the device within a catheter positioned within the mammalian luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the step of percutaneously introducing is performed to position the at least part of the device into the mammalian luminal organ wherein the impedance detector comprises the two detection electrodes positioned in between two excitation electrodes, wherein the known distance between the two detection electrodes is at least 0.5 mm The present disclosure includes disclosure of a method, wherein the steps of operating the impedance detector are performed by operating a frequency generator in communication with the device, the frequency generator selected from the group consisting of an arbitrary waveform generator and two signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, wherein the step of percutaneously introducing is performed by introducing at least part of the device into the mammalian luminal organ selected from the group consisting of a body lumen, a body vessel, a blood vessel, a biliary tract, a urethra, and an esophagus. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. 
     The present disclosure includes disclosure of a method, comprising the steps of operating a device at least partially positioned within a mammalian luminal organ to introduce a first signal having a first frequency into the mammalian luminal organ; obtaining first conductance data using the device to obtain first conductance data in connection with the first signal; operating the device at least partially positioned within a mammalian luminal organ to introduce a second signal having a second frequency into the mammalian luminal organ; obtaining second conductance data using the device to obtain second conductance data in connection with the second signal; operating the device at least partially positioned within a mammalian luminal organ to introduce a third signal having a third frequency into the mammalian luminal organ; obtaining third conductance data using the device to obtain third conductance data in connection with the third signal; and determining a cross-sectional area of the mammalian luminal organ based upon the first conductance data, the second conductance data, the third conductance data, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of a detector of the device. 
     The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the mammalian luminal organ using the determined cross-sectional area and at least one additional cross-sectional area obtained by performing the steps of the method at a different location within the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of blood within the mammalian luminal organ is determined by operating the detector of the device within a catheter positioned within the mammalian luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the steps of operating the device are performed along with operating a frequency generator in communication with the device, the frequency generator selected from the group consisting of an arbitrary waveform generator and two signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. 
     The present disclosure includes disclosure of a method, comprising the steps of operating an impedance device to introduce three signals having different frequencies into a mammalian luminal organ and obtaining conductance data in connection with each of the three signals using an impedance detector of the impedance device; and determining a cross-sectional area of the mammalian luminal organ based upon the conductance data in connection with each of the three signals, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of the impedance detector. 
     The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the mammalian luminal organ using the determined cross-sectional area and at least one additional cross-sectional area obtained by performing the steps of the method at a different location within the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of blood within the mammalian luminal organ is determined by operating the impedance detector of the impedance device within a catheter positioned within the mammalian luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the step of operating is performed along with operating a frequency generator in communication with the impedance device, the frequency generator selected from the group consisting of an arbitrary waveform generator and two signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. 
     The present disclosure includes disclosure of a method, comprising the steps of sequentially introducing a first signal having a first frequency, a second signal having a second frequency, and a third signal having a third frequency into a mammalian luminal organ using a device and detecting conductance data in connection with each signal using the device; and determining a cross-sectional area of the mammalian luminal organ based upon the conductance data in connection with each signal, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of the impedance detector. The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the mammalian luminal organ using the determined cross-sectional area and at least one additional cross-sectional area obtained by performing the steps of the method at a different location within the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of fluid within the mammalian luminal organ is determined by operating the detector of the device within a catheter positioned within the mammalian luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the step of sequentially introducing the frequencies is performed by operating a frequency generator in communication with the device, the frequency generator selected from the group consisting of an arbitrary waveform generator and two signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. 
     The present disclosure includes disclosure of a method, comprising the steps of operating an impedance device to introduce a combined stimulating signal through the detection device into a mammalian luminal organ, the combined stimulating signal comprising a first signal having a first frequency, a second signal having a second frequency, and a third signal having a third frequency, and obtaining output conductance data in connection with each of the three signals using an impedance detector of the impedance device; and determining a cross-sectional area of the mammalian luminal organ based upon the output conductance data in connection with each of the three signals, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of the impedance detector. The present disclosure includes disclosure of a method, further comprising the step of generating a size profile of the mammalian luminal organ using the determined cross-sectional area and at least one additional cross-sectional area obtained by performing the steps of the method at a different location within the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the conductivity of blood within the mammalian luminal organ is determined by operating the impedance detector of the impedance device within a catheter positioned within the mammalian luminal organ by obtaining a conductance measurement within the catheter having a known diameter. The present disclosure includes disclosure of a method, wherein the step of operating is performed along with operating a frequency generator in communication with the impedance device, the frequency generator selected from the group consisting of an arbitrary waveform generator and two signal generators. The present disclosure includes disclosure of a method, wherein the determining step is further performed to determine a parallel tissue conductance. The present disclosure includes disclosure of a method, performed without injecting any fluid into the mammalian luminal organ. The present disclosure includes disclosure of a method, wherein the step of determining the cross-sectional area comprises the step of deconvoluting the output conductance data to obtain a first conductance value, a second conductance value, and a third conductance value from the output conductance data. The present disclosure includes disclosure of a method, wherein the output conductance data comprises a mixed signal, and wherein the step of determining the cross-sectional area further comprises the step of deconvoluting the mixed signal to obtain a first conductance value, a second conductance value, and a third conductance value from the mixed signal. The present disclosure includes disclosure of a method, wherein the first signal, the second signal, and the third signal are sequentially repeated to form a multiplexed signal. 
     The present disclosure includes disclosure of a device, configured to obtain conductance data within a mammalian luminal organ in connection with three signals having different frequencies, wherein the conductance data is sufficient for use to determine a cross-sectional area within the mammalian luminal organ by calculating the cross-sectional area using the conductance data, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of an impedance detector of the device. 
     The disclosure of the present application provides various systems and methods for obtaining parallel tissue conductances within luminal organs. In at least one embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, and injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device. Such a method may further comprise the steps of measuring an output conductance of the first signal and the second signal at the first location using the detector, and calculating a parallel tissue conductance at the first location based in part upon the output conductance and the conductivity of the injected solution. 
     In at least another embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, and measuring a first output conductance of the first signal and the second signal at the first location in connection with a fluid native to the first location, said fluid having a first conductivity. An exemplary method may further comprise the steps of injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance of the first signal and the second signal at the first location in connection with the injected solution, and calculating a parallel tissue conductance at the first location based in part upon the second output conductance and the known conductivity of the injected solution. 
     In at least one embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the step of calculating a parallel tissue conductance comprises the step of calculating a cross-sectional area of the luminal organ at the first location. In another embodiment, the step of introducing a first signal having a first frequency and a second signal having a second frequency is performed using a frequency generator. In an additional embodiment, the frequency generator comprises an arbitrary waveform generator. In yet an additional embodiment, the frequency generator comprises two signal generators. 
     In at least one embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the output conductance comprises a first conductance value and a second conductance value. In an additional embodiment, the first conductance value corresponds to the first frequency and the second conductance value corresponds to the second frequency. In yet an additional embodiment, the step of calculating a cross-sectional area comprises the step of deconvoluting the output conductance to obtain a first conductance value and a second conductance value from the output conductance. 
     In at least one embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the output conductance comprises a mixed signal. In another embodiment, the step of calculating a cross-sectional area further comprises the step of deconvoluting the mixed signal to obtain a first conductance value and a second conductance value from the mixed signal. In yet another embodiment, the first signal and the second signal are repeatedly alternated to form a multiplexed signal. In an additional embodiment, the first signal and the second signal are separated in time by less than 100 milliseconds. In yet an additional embodiment, the first signal and the second signal are separated in time by less than 10 milliseconds. In another embodiment, the first signal and the second signal are combined to form a combined signal. 
     In at least one embodiment of a single solution injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the first location comprises a plaque site. In another embodiment, the step of calculating a parallel tissue conductance comprises the step of determining plaque-type composition of a plaque at the plaque site. In yet another embodiment, the luminal organ is selected from the group consisting of a body lumen, a body vessel, a blood vessel, a biliary tract, a urethra, and an esophagus. In an additional embodiment, the detector comprises two detection electrodes positioned in between two excitation electrodes, wherein the two excitation electrodes are capable of producing an electrical field. In yet another embodiment, the method further comprises the steps of moving the detection device to a second location within the luminal organ, injecting the solution into the luminal organ at or near the detector of the detection device, measuring a second output conductance of the first signal and the second signal at the second location using the detection device, calculating a second parallel tissue conductance at the second location based in part upon the output conductance and the conductivity of the injected solution, calculating a second cross-sectional area of the luminal organ at the second location, and determining a profile of the luminal organ indicative of the first location and the second location based upon the calculated cross-sectional area and the calculated second cross-sectional area. 
     In at least one embodiment of a single solution injection method to determine a cross-sectional area of a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring an output conductance of the first signal and the second signal at the first location using the detector, and calculating a cross-sectional area of the luminal organ at the first location based in part upon the output conductance and the conductivity of the injected solution. 
     In at least one embodiment of a single solution injection method to assess the composition of a plaque within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a plaque site, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring an output conductance of the first signal and the second signal at the plaque site using the detector, and determining plaque-type composition of a plaque at the plaque site based in part upon the output conductance and the conductivity of the injected solution. 
     In at least one embodiment of a single injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, measuring a first output conductance of the first signal and the second signal at the first location in connection with a fluid native to the first location using the detector, said fluid having a first conductivity, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance of the first signal and the second signal at the first location in connection with the injected solution using the detector, and calculating a parallel tissue conductance at the first location based in part upon the second output conductance and the known conductivity of the injected solution. In another embodiment, the step of calculating the parallel tissue conductance is further based in part upon the first output conductance and the native conductivity of the native fluid. In yet another embodiment, the step of calculating the parallel tissue conductance comprises the step of deconvoluting the second output conductance to obtain a first resulting conductance value and a second resulting conductance value from the second output conductance. In an additional embodiment, the step of calculating a parallel tissue conductance comprises the step of calculating a cross-sectional area of the luminal organ at the first location. In yet an additional embodiment, the first location comprises a plaque site. In another embodiment, the step of calculating a parallel tissue conductance comprises the step of determining plaque-type composition of a plaque at the plaque site. 
     In at least one embodiment of a single injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device, obtaining a first output conductance indicative of a bodily fluid native to the luminal organ using the detector, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance indicative of the injected solution using the detector, and calculating a parallel tissue conductance based in part upon the first output conductance, the second output conductance, and the known conductivity of the injected solution. In another embodiment, the step of calculating the parallel tissue conductance is further based in part upon a conductivity of the bodily fluid native to the luminal organ. In yet another embodiment, the step of calculating the parallel tissue conductance further comprises the step of calculating a cross-sectional area of the luminal organ at the first location. In an additional embodiment, the step of calculating the cross-sectional area is based in part upon a known distance between detection electrodes of the detector. 
     In at least one embodiment of a single injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the first output conductance is further indicative of a known diameter of a lumen defined within the detection device. In an additional embodiment, the first output conductance is further indicative of a known cross-sectional area of a lumen defined within the detection device. In yet an additional embodiment, the first location comprises a plaque site. In another embodiment, the step of calculating the parallel tissue conductance further comprises the step of determining plaque-type composition of a plaque at the plaque site. 
     In at least one embodiment of a single injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method further comprises the steps of moving the detection device to a second location within the luminal organ, injecting the solution into the luminal organ at or near the detector of the detection device, measuring a third output conductance indicative of the injected solution using the detector, calculating a second parallel tissue conductance based in part upon the first output conductance, the third output conductance, and the known conductivity of the injected solution, calculating a second cross-sectional area of the luminal organ at the second location, and determining a profile of the luminal organ indicative of the first location and the second location based upon the calculated cross-sectional area and the calculated second cross-sectional area. 
     In at least one embodiment of a single injection method to determine a cross-sectional area of a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device, obtaining a first output conductance indicative of a bodily fluid native to the luminal organ using the detector, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance indicative of the injected solution using the detector, and calculating a cross-sectional area of the luminal organ at the first location based in part upon the first output conductance, the second output conductance, and the known conductivity of the injected solution. In another embodiment, the step of calculating the cross-sectional area is further based in part upon a conductivity of the bodily fluid native to the luminal organ. In yet another embodiment, the step of calculating the cross-sectional area is further based in part upon a known distance between detection electrodes of the detector. In an additional embodiment, the first output conductance is further indicative of a known diameter of a lumen defined within the detection device. In yet an additional embodiment, the first output conductance is further indicative of a known cross-sectional area of a lumen defined within the detection device. 
     In at least one embodiment of a single injection method to obtain a parallel tissue conductance within a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a first output conductance indicative of the injected solution using the detector, obtaining a second output conductance indicative of a bodily fluid native to the luminal organ using the detector, and calculating a parallel tissue conductance based in part upon the first output conductance, the second output conductance, and the known conductivity of the injected solution. 
     In at least one embodiment of a single injection method to determine a cross-sectional area of a luminal organ of the present disclosure, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a first output conductance indicative of the injected solution using the detector, obtaining a second output conductance indicative of a bodily fluid native to the luminal organ using the detector, and calculating a cross-sectional area of the luminal organ at the first location based in part upon the first output conductance, the second output conductance, and the known conductivity of the injected solution. 
     In at least one embodiment of a single injection method to determine a cross-sectional area of a luminal organ, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a first location, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, measuring a first output conductance of the first signal and the second signal at the first location in connection with a fluid native to the first location, said fluid having a first conductivity, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance of the first signal and the second signal at the first location in connection with the injected solution, and calculating a cross-sectional area of the luminal organ at the first location based in part upon the second output conductance and the known conductivity of the injected solution. 
     In at least one embodiment of a single injection method to assess the composition of a plaque within a luminal organ, the method comprises the steps of introducing at least part of a detection device into a luminal organ at a plaque site, the detection device having a detector, applying current to the detection device using a stimulator, introducing a first signal having a first frequency and a second signal having a second frequency through the detection device, measuring a first output conductance of the first signal and the second signal at the first location in connection with a fluid native to the first location, said fluid having a first conductivity, injecting a solution having a known conductivity into the luminal organ at or near the detector of the detection device, measuring a second output conductance of the first signal and the second signal at the first location in connection with the injected solution, and determining plaque-type composition of a plaque at the plaque site based in part upon the second output conductance and the known conductivity of the injected solution. 
     In at least one embodiment of a system to obtain a parallel tissue conductance within a luminal organ, the system comprises a detection device having a detector, and a frequency generator coupled to the detection device. In another embodiment, the detector is capable of measuring an output conductance. In yet another embodiment, the detector comprises two detection electrodes positioned in between two excitation electrodes. In an additional embodiment, the two excitation electrodes are capable of producing an electrical field. In yet an additional embodiment, the frequency generator is capable of generating signals having at least two distinct frequencies through the detection device. 
     In at least one embodiment of a system to obtain a parallel tissue conductance within a luminal organ, the system further comprises a deconvolution device. In an additional embodiment, the deconvolution device is capable of deconvoluting an output conductance to obtain a first conductance value and a second conductance value from the output conductance. In yet an additional embodiment, the system further comprises a stimulator coupled to the detection device. In another embodiment, the stimulator is capable of exciting a current to the detection device. 
     In at least one embodiment of a system to obtain a parallel tissue conductance within a luminal organ, the system further comprises a data acquisition and processing system coupled to the detection device. In another embodiment, the data acquisition and processing system is capable of receiving conductance data from the detector and calculate parallel tissue conductance. In yet another embodiment, the data acquisition and processing system is further capable of calculating a cross-sectional area of a luminal organ based upon the conductance data. In an additional embodiment, the data acquisition and processing system is further capable of determining plaque-type composition of a plaque within a luminal organ based upon the conductance data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the flow of a dual frequency stimulus to obtain a dual conductance which can subsequently be deconvoluted, according to an embodiment of the present disclosure; 
         FIG. 2A  shows an exemplary system for obtaining a parallel tissue conductance within a luminal organ according to an embodiment of the present disclosure; 
         FIG. 2B  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ having impedance measuring electrodes supported in front of a stenting balloon thereon, according to an embodiment of the present disclosure; 
         FIG. 2C  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ having impedance measuring electrodes within and in front of a balloon thereon, according to an embodiment of the present disclosure; 
         FIG. 2D  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ having an ultrasound transducer within and in front of a balloon thereon, according to an embodiment of the present disclosure; 
         FIG. 2E  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ without a stenting balloon, according to an embodiment of the present disclosure; 
         FIG. 2F  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ having wire and impedance electrodes, according to an embodiment of the present disclosure; 
         FIG. 2G  shows an exemplary detection device of an exemplary system for obtaining a parallel tissue conductance within a luminal organ having multiple detection electrodes, according to an embodiment of the present disclosure; 
         FIGS. 2H and 2I  show at least a portion of an exemplary systems for obtaining a parallel tissue conductance within a luminal organ according to embodiments of the present disclosure; 
         FIG. 3  shows steps of an exemplary method for obtaining a parallel tissue conductance within a luminal organ using a single injection method according to an embodiment of the present disclosure; 
         FIG. 4  shows steps of another exemplary method for obtaining a parallel tissue conductance within a luminal organ using a single injection method according to an embodiment of the present disclosure; 
         FIG. 5A  shows a balloon distension of the lumen of a coronary artery according to an embodiment of the present disclosure; and 
         FIG. 5B  shows a balloon distension of a stent into the lumen of a coronary artery according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended. 
     CSA and Gp 
     The present disclosure provides for systems and methods for obtaining parallel tissue conductances to, for example, measure cross-sectional areas and pressure gradients in luminal organs such as, for example, blood vessels, heart valves, and other visceral hollow organs. A two injection method allowing for the simultaneous determination of cross-sectional area (CSA) and parallel conductance (G p ) of luminal organs are currently known in the art by way of U.S. Pat. No. 7,454,244 to Kassab. As referenced therein, each injection provides a known conductivity-conductance (σ−G) relation or equation as per an Ohm&#39;s law modification that accounts for parallel conductance (namely current losses from the lumen of vessel): 
         G =(CSA/L)σ+ G   p    [1]
 
     wherein G is the total conductance, CSA is the cross-sectional area of the luminal organ (which may include, but is not limited to, various bodily lumens and vessels, including blood vessels, a biliary tract, a urethra, and an esophagus, for example), L is a constant for the length of spacing between detection electrodes of the detection device used, σ is the specific electrical conductivity of the fluid, and G p  is the parallel conductance (namely the effective conductance of the structure outside of the fluid). 
     Mathematically, two equations (corresponding to two injections) and two unknowns produce a deterministic solution for CSA and G p . Normal and half-normal saline solutions, for example, are routinely used clinically and therefore are the logical choice for varying the σ−G relation to produce two equations for the two unknowns. 
     In order to reduce the number of steps that a clinician must perform, it would be ideal to reduce the number of injections. The disclosure of the present application addresses the same, providing a clinician with the alternative of using a single injection instead of being required to use two injections to determine cross-sectional areas of luminal organs. 
     The following analysis allows a single injection of saline to provide the desired CSA and G p . The additional equations referenced below are generated through multiple stimulating frequency injections; i.e., the system performs multiple current injections at baseline (in blood) and during a single saline injection. The system then determines the response (conductance) to both frequencies which allows the calculation of CSA and G p  uniquely. 
     To facilitate these determinations, the following axioms or facts established in the art are considered: (i) the conductivity of blood, σ b , does not vary over stimulating or excitation frequencies in the range of 2-100 kHz; (ii) muscle/vessel becomes more conductive when frequency is greater than 12 kHz; and (iii) saline conductivity varies as a power relation with frequency. 
     A premise of the disclosure of the present application is to stimulate with dual frequency to provide the appropriate number of equations to solve for the desired parameters (CSA and G p ). For example, consider a waveform of two different frequencies (e.g., 3 and 10 kHz) as the excitation frequencies as shown in  FIG. 1 . If those stimulating frequencies are applied to Equation [1], one will obtain the following: 
     In blood (b): 
         G   1   b =(CSA/L)σ b   +G   1   p    [2]
 
       and 
         G   2   b =(CSA/L)σ b   +G   2   p    [3]
 
     where 1 and 2 correspond to the two different frequencies, respectively; and 
     During Saline(s) Injection: 
         G   1   s =(CSA/L)σ 1   s   +G   1   p    [4]
 
       and 
         G   2   s =(CSA/L)σ s   2   +G   2   p    [5]
 
     The only assumption applicable to the foregoing is that the parallel conductance (G p ) is the same with blood or blood which is physically reasonable and has been proven for the heart muscle. As referenced above, L is known from the device design (guidewire or catheter, for example), σ 1   s  and σ 2   s  represent calibration constants measured for the device, and G 1   b , G 2   b , G 1   s , and G 2   s  are measured for baseline blood and during the saline injection. Therefore, there are four remaining unknowns: CSA, G 1   p , G 2   p , and σ b . Since there are four applicable equations (Equations [2-5]), the problem is therefore mathematically well posed and deterministic. If the change of parallel conductance (G p ) with frequency is relatively small, then Equations [2] and [3] become unnecessary and Equations [4] and [5] reduce to: 
         G   1   s =(CSA/L)σ 1   s   +G   1   p    [6]
 
       and 
         G   2   s =(CSA/L)σ 2   s   +G   p    [7]
 
     which becomes analogous to the two saline injections but with one saline injection at two different frequencies. 
     In general, four equations can be set up as a matrix of the form Ax=b: 
     
       
         
           
             
               
                 
                   
                     
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     wherein A is the 4×4 matrix of known quantities, x is the 1×4 matrix of unknown quantities (CSA, σ b , G p   1 , G p   2 ), and b is the 1×4 matrix of known quantities. 
     A single injection method may also be utilized in accordance with the following, whereby the desired CSA and G p  can be obtained with two equations, one stemming from a fluid injection (such as saline), and the other stemming from measured blood conductivity. Using such an exemplary embodiment of a single injection method, and as referenced generally above, blood conductivity can be measured for each patient by recording the electrical conductance within the device (such as an introducer catheter, for example) with known dimensions. Ohm&#39;s law can then be used in the catheter, wherein G p =0, as follows: 
         G =(CSA/L)σ b    [8]
 
     Since G can be measured within the catheter (which is then already inserted in the body of the patient) having a known diameter or CSA, and since L (the distance between detection electrodes) is also a known parameter, σ b  (the conductivity of blood) can determined for each patient prior to advancing the device to the site of interest for sizing measurements. Some example measurements obtained during swine testing provided values that range from 0.827-0.899 (with average of 0.866 in appropriate units) in one animal and values that range from 0.871-0.889 (with average of 0.866) in another animal. These compare to mean values of 0.694 and 1.362 for 0.45% and 0.9% NaCl (in the same units), respectively. Blood conductivity is intermediate to normal and half normal saline. 
     With the average σ b  known, Equation [1] can then be rewritten as: 
         G   s =(CSA/L)σ s   +G   p    [9]
 
       and 
         G   b =(CSA/L)σ b   +G   2   p    [10]
 
     wherein G s  and G b  correspond to electrical conductance measurements in the presence of saline (s) and blood (b), respectively. These solution to such a 2×2 matrix is then identified as 
     
       
         
           
             
               
                 
                   
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     Experimental measurements in swine using the two injection method as referenced above compared to present one injection method compare very well within accepted error tolerance. For example, studies using said one injection method resulted in an obtained mean value of 5.7±0.22 mm (from several blood vessel measurements that ranged from 5.53 to 5.95 mm), and 5.2±0.22 mm (from the same measurements that ranged from 5.01 to 5.41 mm for three respective blood vessel measurements) using the aforementioned two injection method. The actual blood vessel measurement was 5.4 mm, and both methods were within 5% of the actual measurement. 
     In at least one embodiment of a single injection method of the present disclosure, the injection includes adenosine. Adenosine, used in said method, can also provide hyperemic velocity measurements to determine coronary flow reserve and in turn fractional flow reserve as previously outlined. 
     The present single injection method has a number of significant and non-obvious differences as compared to prior two injection methods. Instead of using 0.45% NaCl (or some other known salinity or fluid conductivity), the present single injection method uses the patient&#39;s own blood with patient-specific blood conductivity as determined in the catheter in vivo prior to measurement. In addition, a single saline injection containing adenosine that provides the sizing also provides the hyperemic velocity measurements as referenced herein. 
     The present disclosure allows for accurate measurements of the luminal cross-sectional area of organ stenosis within acceptable limits to enable accurate and scientific stent sizing and placement in order to improve clinical outcomes by avoiding under or over deployment and under or over sizing of a stent which can cause acute closure or in-stent re-stenosis. In an exemplary embodiment, an angioplasty or stent balloon positioned upon the device (catheter or wire, for example) includes impedance electrodes supported by the catheter in front of the balloon. These electrodes enable the immediate measurement of the cross-sectional area of the vessel during the balloon advancement, providing a direct measurement of non-stenosed area and allowing the selection of the appropriate stent size. In one approach, error due to the loss of current in the wall of the organ and surrounding tissue is corrected by injection of a saline solutions or other solutions with a known conductivities. In at least one embodiment, impedance electrodes are located in the center of the balloon in order to deploy the stent to the desired cross-sectional area. These embodiments and procedures substantially improve the accuracy of stenting and the outcome and reduce the cost. 
     Other embodiments make diagnosis of valve stenosis more accurate and more scientific by providing a direct accurate measurement of cross-sectional area of a valve annulus, independent of the flow conditions through the valve. Other embodiments improve evaluation of cross-sectional area and flow in organs like the gastrointestinal tract and the urinary tract 
     Embodiments of the present disclosure overcome the problems associated with determination of the size (cross-sectional area) of luminal organs, such as, for example, in the coronary arteries, carotid, femoral, renal and iliac arteries, aorta, gastrointestinal tract, urethra and ureter. Exemplary embodiments also provide methods for registration of acute changes in wall conductance, such as, for example, due to edema or acute damage to the tissue, and for detection of muscle spasms/contractions. 
     As referenced herein, and in at least one exemplary embodiment, there is provided an angioplasty catheter with impedance electrodes near the distal end of the catheter (in front of the balloon, for example) for immediate measurement of the cross-sectional area of a vessel lumen during balloon advancement. Such a catheter would include electrodes for accurate detection of organ luminal cross-sectional area and ports for pressure gradient measurements. Hence, it is not necessary to change catheters such as with the current use of intravascular ultrasound. 
     In an exemplary embodiment, such a catheter provides direct measurement of the non-stenosed area, thereby allowing the selection of an appropriately sized stent. In another embodiment, additional impedance electrodes may be incorporated in the center of the balloon on the catheter in order to deploy the stent to the desired cross-sectional area. The procedures described herein substantially improve the accuracy of stenting and improve the cost and outcome as well. 
     In another exemplary embodiment, the impedance electrodes are embedded within a catheter to measure the valve area directly and independent of cardiac output or pressure drop and therefore minimize errors in the measurement of valve area. As such, measurements of area are direct and not based on calculations with underlying assumptions. In another exemplary embodiment, pressure sensors can be mounted proximal and distal to the impedance electrodes to provide simultaneous pressure gradient recording. 
     Plaque-Type and G p    
     The disclosure of the present application further provides systems and methods for determining the type and/or composition of a plaque that may be engaged within a blood vessel, permitting accurate and reproducible measurements of the type or composition of plaques in blood vessels within acceptable limits. The understanding of a plaque type or composition allows a health care professional to better assess the risks of the plaque dislodging from its position and promoting infarct downstream. For example, the disclosure of the present application enables the determination of a plaque type and/or composition in order to improve patient health by allowing early treatment options for undersized (but potentially dangerous) plaques that could dislodge and cause infarcts or other health problems. As discussed above, such determination of plaque information allows for removal or other disintegration of a smaller plaque that may otherwise not be of concern under conventional thought merely because of its smaller size. However, smaller plaques, depending on their composition, are potentially lethal, and the disclosure of the present application serves to decrease the ill effects of such plaques by assessing their type and composition when they are still “too small” to be of concern for standard medical diagnoses. 
     G p  is a measure of electrical conductivity through the tissue and is the inverse of electrical resistivity. Fat or lipids have a higher resistivity to electrical flow or a lower G p  than compared to most other issues. For example, lipids have approximately ten times (10×) higher resistivity or ten times (10×) lower conductivity than vascular tissue. In terms of conductivities, fat has a 0.023 S/m value, blood vessel wall has 0.32 S/m, and blood has a 0.7 S/m. Because unstable plaques are characterized by a higher lipid core, at least one purpose of the disclosure of the present application is to allow a clinician, for example, to use the value of G p  to identify vulnerable plaque. 
     Studies indicate that G p  is about 70-80% for a normal vessel. This value is significantly reduced when lipid is present in the vessel wall. In other words, the lipid insulates the vessel and significantly reduces the current loss through the wall. The degree of reduction of G will be dependent on the fraction of lipid in the plaque. The higher the fraction of lipid, the smaller the value of G p , and consequently the greater the risk of plaque rupture which can cause acute coronary syndrome. Thus, the exemplary embodiments described throughout this disclosure are used to develop a measure for the conductance, G p , which in turn is used as a determinant of the type and/or composition of the plaque in the region of measurement. 
     In an exemplary embodiment, the data on parallel conductance as a function of longitudinal position along the vessel can be exported from an electronic spreadsheet, such as, for example, a Microsoft Excel file, to a diagramming software, such as AutoCAD, where the software uses the coordinates to render the axial variation of G p  score (% G p ). 
     Furthermore, the G p  score may be scaled through a scaling model index to simplify its relay of information to a user. An example of a scaling index used in the present disclosure is to designate a single digit whole number to represent the calculated conductance G p . In such a scaling index, for example, “0” would designated a calculated G p  of 0-9%; “1” would designate a calculated G p  of 10-19%; “2” would designate a calculated G p  of 20-29%; . . . ; and “9” would designate a calculated G p  of 90-100%. In this scaling index example, a designation of 0, 1, 2, 3, 4, 5 or 6 would represent a risky plaque composition, with the level of risk decreasing as the scaling number increases, because the generally low level of conductance meaning generally higher fat or lipid concentrations. In contrast, a designation of 7, 8 or 9 would generally represent a non-risky plaque composition, with the level of risk decreasing as the scaling number increases, because the generally higher level of conductance meaning generally lower fat or lipid concentrations. 
     For example, for a given determination of a conductance value of 68%, the resultant plaque type would be deemed as “6” or somewhat fatty. This would be a simple automated analysis of the plaque site under consideration based on the teachings and discoveries of the present disclosure as described throughout this disclosure. Of course, the range for the scaling model described above could be pre-set by the manufacturer according to established studies, but may be later changed by the individual clinic or user based on further or subsequent studies. 
     G p  and other relevant measures such as distensibility, tension, etc., may then appear on a computer screen, and the user can then remove the stenosis by distension or by placement of a stent. The value of G p , which reflects the “hardness” (high G p ) or “softness” (low G p ), can be used in selection of high or low pressure balloons as known in the arts. 
     Regarding plaque-type determination using two different frequencies (3 kHz and 10 kHz, for example), solving the above-referenced matrix provides for a ratio of parallel conductance at the two frequencies to assess plaque-type. Regarding the matrix, the solutions of unknown quantities can be provided as follows: 
       σ b   =[L ( G   b   2 +((G s   2 σ 1   s   −G   1   s σ 2   s )/(σ 2   s −σ 1   s ))]/CSA   [13]
 
       CSA= L ( G   s   1   −G   2   s )/(σ 1   s −σ 2   s )   [14]
 
         G   p   1 =( G   b   1   −G   b   2 )−(( G   s   2 σ 1   s   −G   1   s σ 2   s )/(σ 1   s −σ 2   s ))   [15]
 
         G   p   2 =(G s   2 σ 1   s   −G   1   s σ 2   s )/(σ 1   s −σ 2   s )   [16]
 
     The ratio of parallel conductance at the two different frequency is given by: 
       [ G   p   2   ]/[G   p   1 ]=(G s   2 σ 1   s   −G   1   s σ 2   s )/(( G   b   1   −G   b   2   +G   s   2 )σ 1   s −( G   b   1   −G   b   2   +G   s   1 )σ 2   s )   [17]
 
     This ratio (Equation [17]) can be used to assess plaque composition. In a normal vessel, the ratio of parallel conductance at two frequencies (3 kHz and 10 kHz, for example) is 4.8 or roughly 5. If the vessel was entirely surrounded by fat (a lipid lesion), the ratio would reduce to 1.03 or roughly 1. Hence, the ratio of parallel conductance at the two frequencies can be used as an index of lipid composition where 1 (completely lipid) and 5 (no lipid) similar to previous scale referenced herein. In summary, the first sale referenced above shows that a reduction of parallel conductance at any given frequency implies the presence of lipid to different extent, and this second scale considers the dependence of parallel conductance on frequency (with almost constant or no change with frequency suggesting high lipid composition), providing two orthogonal parameters to characterize the lesion composition. 
     In use, an exemplary system of the present disclosure provides a user with an effective and powerful tool to relay information about a vessel site and any plaque housed therein. A user could first consider the CSA level as an exemplary device is pulled through the site or as numerous electrodes calculate the CSA as their designated cross-sectional place, as described generally herein. If there is little to no changes in the CSA value, then the user could acknowledge that there is little to no obstructions or plaques within the lumen of the blood vessel. However, if there is some change in the value of the CSA, then the conductance measurement and plaque type information could be monitored to determine the extent to which plaque formation is present as well as the type of plaque, as determined by the scaling model whole number displayed, as described herein. 
     Reference will now be made to the various systems and methods of the present disclosure as shown in the figures.  FIG. 1  shows a schematic for using signals having differing frequencies in accordance with the present disclosure to allow for the calculation of CSA within a luminal organ. As shown in  FIG. 1 , two input signals having different frequencies (I 1  and I 2 ) are combined to form one combined stimulating signal (I 1+2 ). When the combined stimulating signal flows through, for example, a detection device  202  (as referenced below in  FIG. 2A ), an output conductance (G 1+2 ) in response to said stimulating signal may be obtained. Such an output conductance, absent of any solution injection, would be indicative of the conductance of the fluid native to the area (blood, for example). If such a signal flows through the device during the time of a saline injection, for example, the output conductance would be indicative of the saline solution. 
     Such an output (of dual conductances) can lead to the following. The b matrix values are shown in  FIG. 1  for blood and saline and can be determined accordingly. Once A and b are inputted, x can be solved in conventional way to determine the CSA and parallel conductance (G p ). As shown in  FIG. 1 , the combined response can be deconvoluted to produce the desired parameters to calculate the CSA and parallel conductance simultaneously. 
     An exemplary system for obtaining a parallel tissue conductance within a luminal organ of the present disclosure is shown in  FIG. 2A . As shown in  FIG. 2A , an exemplary embodiment of a system  200  of the present disclosure comprises a detection device  202  having a detector  204 , and a frequency generator  206  coupled to detection device  202 . Frequency generator  206 , in at least one embodiment, is capable of generating signals having at least two distinct frequencies through detection device  202 . An exemplary frequency generator  206  may include, but is not limited to, an arbitrary waveform generator or two signal generators. In at least one embodiment of an arbitrary waveform generator, the output conductance can be filtered at the appropriate frequency to derive the desired conductance for each frequency. In at least one embodiment of system  200  of the present disclosure, detector  204  comprises detection electrodes  26 ,  28  positioned in between excitation electrodes  25 ,  27 , wherein excitation electrodes  25 ,  27  are capable of producing an electrical field. 
     In an exemplary embodiment of system  200 , system  200  further comprises a deconvolution device  216 , whereby deconvolution device  216  is capable of filtering an output conductance to obtain a first conductance value and a second conductance value from the output conductance, and/or whereby deconvolution device  216  is capable of filtering an output frequency to obtain a first resulting frequency and a second resulting frequency from the output frequency. Deconvolution device  216  may be coupled to any number of elements of system  200 , including, but not limited to, detection device  202 , detector  204 , and/or frequency generator  206 . In the exemplary embodiment of system  200  shown in  FIG. 2A , deconvolution device is shown as being coupled to detection device  202 . 
     Furthermore, and in an exemplary embodiment of a system  200  of the present disclosure, system  200  may further comprise a stimulator  218  capable of applying/exciting a current to detection device  202 . An exemplary system  200  of the present disclosure may also comprise a data acquisition and processing system  220  capable of receiving conductance data from detector  204  and calculating parallel tissue conductance. In various embodiments of data acquisition and processing systems  220 , data acquisition and processing systems  220  may be further capable of calculating a cross-sectional area of a luminal organ and/or determining plaque-type composition of a plaque within a luminal organ, based upon the conductance data. Data acquisition and processing systems  220  of the present disclosure are considered to have a processor (processing means), memory, and a storage device (storage means) therein, such as a typical “computer” known in the art would have. Data acquisition and processing systems  220  of the present disclosure are therefore configured to receive data (such as conductance or impedance data) and process the same, such as being programmed to calculate parallel tissue conductance and/or cross-sectional area based on said conductance or impedance data. 
     In addition, an exemplary detection device  202  of the present disclosure may comprise any number of devices  202  as shown in  FIGS. 2B-2G . Referring to  FIGS. 2B, 2C, 2D, and 2E , several exemplary embodiments of the detection devices  202  are illustrated. The detection devices  202  shown contain, to a varying degree, different electrodes, number and optional balloon(s). With reference to the embodiment shown in  FIG. 2B , there is shown an impedance catheter  20  (an exemplary detection device  202 ) with four electrodes  25 ,  26 ,  27  and  28  placed close to the tip  19  of the catheter  20 . Proximal to these electrodes is an angiography or stenting balloon  30  capable of being used for treating stenosis. Electrodes  25  and  27  are excitation electrodes, while electrodes  26  and  28  are detection electrodes, which allow measurement of cross-sectional area during advancement of detection device  202 , as described in further detail below. The portion of catheter  20  within balloon  30  includes an infusion port  35  and a pressure port  36 . 
     Catheter  20  may also advantageously include several miniature pressure transducers (not shown) carried by the catheter or pressure ports for determining the pressure gradient proximal at the site where the CSA is measured. The pressure may be measured inside the balloon and proximal, distal to and at the location of the cross-sectional area measurement, and locations proximal and distal thereto, thereby enabling the measurement of pressure recordings at the site of stenosis and also the measurement of pressure-difference along or near the stenosis. In at least one embodiment, and as shown in  FIG. 2B , catheter  20  includes pressure port  90  and pressure port  91  proximal to or at the site of the cross-sectional measurement for evaluation of pressure gradients. As described below with reference to  FIGS. 2H, 2I, and 2J , and in at least one embodiment, pressure ports  90 ,  91  are connected by respective conduits in catheter  20  to pressure sensors within system  200 . Such pressure sensors are well known in the art and include, for example, fiber-optic systems, miniature strain gauges, and perfused low-compliance manometry. 
     In at least one embodiment, a fluid-filled silastic pressure-monitoring catheter is connected to a pressure transducer. Luminal pressure can be monitored by a low compliance external pressure transducer coupled to the infusion channel of the catheter. Pressure transducer calibration may be carried out by applying 0 and 100 mmHg of pressure by means of a hydrostatic column, for example. 
     In an exemplary embodiment, and shown in  FIG. 2C , catheter  39  includes another set of excitation electrodes  40 ,  41  and detection electrodes  42 ,  43  located inside the angioplastic or stenting balloon  30  for accurate determination of the balloon cross-sectional area during angioplasty or stent deployment. These electrodes are in addition to electrodes  25 ,  26 ,  27  and  28 . 
     In another exemplary embodiment, and as shown in  FIG. 2G , several cross-sectional areas can be measured using an array of  5  or more electrodes. Here, the excitation electrodes  51 ,  52 , are used to generate the current while detection electrodes  53 ,  54 ,  55 ,  56  and  57  are used to detect the current at their respective sites. 
     The tip of an exemplary catheter can be straight, curved or with an angle to facilitate insertion into the coronary arteries or other lumens, such as, for example, the biliary tract. The distance between the balloon and the electrodes is usually small, in the 0.5-2 cm range, but can be closer or further away, depending on the particular application or treatment involved. 
     In at least another embodiment, and shown in  FIG. 2D , catheter  21  has one or more imaging or recording device, such as, for example, ultrasound transducers  50  for cross-sectional area and wall thickness measurements. As shown in this exemplary embodiment, transducers  50  are located near the distal tip  19  of catheter  21 . 
       FIG. 2E  shows an exemplary embodiment of an impedance catheter  22  without an angioplastic or stenting balloon. This catheter  22  also comprises an infusion or injection port  35  located proximal relative to the excitation electrode  25  and pressure port  36 . 
     With reference to the exemplary embodiment shown in  FIG. 2F , electrodes  25 ,  26 ,  27 ,  28  can also be built onto a wire  18 , such as, for example, a pressure wire, and inserted through a guide catheter  23  where the infusion of bolus can be made through the lumen of the guide catheter  37 . Various wire  18  embodiments can be used separately (i.e., without a catheter), or can be used in connection with a guide catheter  37  as shown in  FIG. 2E . 
     With reference to the embodiments shown in  FIGS. 2B-2G , the impedance catheter advantageously includes optional ports  35 ,  36 ,  37  for suction of contents of the organ or infusion of fluid. Suction/infusion ports  35 ,  36 ,  37  can be placed as shown with the balloon or elsewhere both proximal or distal to the balloon on the various catheters. The fluid inside the balloon may be any biologically compatible conducting fluid. The fluid to inject through the infusion port or ports can be any biologically compatible fluid but the conductivity of the fluid is selected to be different from that of blood (e.g., saline). 
     In at least another embodiment (not illustrated), an exemplary catheter contains an extra channel for insertion of a guide wire to stiffen the flexible catheter during the insertion or data recording. In yet another embodiment (not illustrated), the catheter includes a sensor for measurement of the flow of fluid in the body organ. 
     As described below with reference to  FIGS. 2H, 2I, and 2J , the excitation and detection electrodes are electrically connected to electrically conductive leads in the catheter for connecting the electrodes to the stimulator  218 , for example. 
       FIGS. 2H and 2I  illustrate two exemplary embodiments  20 A and  20 B of the catheter in cross-section. Each embodiment has a lumen  60  for inflating and deflating a balloon and a lumen  61  for suction and infusion. The sizes of these lumens can vary in size. The impedance electrode electrical leads  70 A are embedded in the material of the catheter in the embodiment in  FIG. 2H , whereas the electrode electrical leads  70 B are tunneled through a lumen  71  formed within the body of catheter  70 B in  FIG. 2I . 
     Pressure conduits for perfusion manometry connect the pressure ports  90 ,  91  to transducers included in system  200 . As shown in  FIG. 2H , pressure conduits  95 A may be formed in  20 A. In another exemplary embodiment, shown in FIG. 2 I, pressure conduits  95 B constitute individual conduits within a tunnel  96  formed in catheter  20 B. In the embodiment described above where miniature pressure transducers are carried by the catheter, electrical conductors will be substituted for these pressure conduits. 
     At least a portion of an exemplary system for obtaining a parallel tissue conductance within a luminal organ of the present disclosure is shown in  FIG. 2J . As shown in  FIG. 2J , an exemplary system  200  of the present disclosure comprises a detection device operably connected to a manual or automatic system  222  for distension of a balloon and to a system  224  for infusion of fluid or suction of blood. The fluid, in an exemplary embodiment, may be heated to 37-39° C. or equivalent to body temperature with heating unit  226 . In addition, and as shown in  FIG. 2J , system  200  may comprise a stimulator  218  to provide a current to excite detection device  202 , and a data acquisition and processing system  220  to process conductance data. Furthermore, an exemplary system  200  may also comprise a signal amplifier/conditioner (not shown) and a computer  228  for additional data processing as desired. Such a system  200  may also optionally contain signal conditioning equipment for recording of fluid flow in the organ. 
     In an exemplary embodiment, the system  200  is pre-calibrated and the detection device  202  is available in a package. In such an embodiment, for example, the package may also contains sterile syringes with the fluid(s) to be injected. The syringes, in an exemplary embodiment, may be attached to heating unit  226 , and after heating of the fluid by heating unit  226  and placement of at least part of detection device  202  in the luminal organ of interest, the user presses a button that initiates the injection with subsequent computation of the desired parameters. The parallel conductance, CSA, plaque-type, and other relevant measures such as distensibility, tension, etc., may then typically appear on the display of computer  228 . In such an embodiment, the user can then remove the stenosis by distension or by placement of a stent. 
     If more than one CSA is measured, for example, system  200  can also contain a multiplexer unit or a switch between CSA channels. In at least one embodiment, each CSA measurement will be through separate amplifier units. The same may account for the pressure channels as well. 
     In at least one embodiment, the impedance and pressure data are analog signals which are converted by analog-to-digital converters  230  and transmitted to a computer  228  for on-line display, on-line analysis and storage. In another embodiment, all data handling is done on an entirely analog basis. The analysis may also includes software programs for reducing the error due to conductance of current in the organ wall and surrounding tissue and for displaying the 2D or 3D-geometry of the CSA distribution along the length of the vessel along with the pressure gradient. In an exemplary embodiment of the software, a finite element approach or a finite difference approach is used to derive the CSA of the organ stenosis taking parameters such as conductivities of the fluid in the organ and of the organ wall and surrounding tissue into consideration. In another embodiment, the software contains the code for reducing the error in luminal CSA measurement by analyzing signals during interventions such as infusion of a fluid into the organ or by changing the amplitude or frequency of the current from the constant current amplifier. The software chosen for a particular application, preferably allows computation of the CSA with only a small error instantly or within acceptable time during the medical procedure. 
     Steps of an exemplary single injection method of the present disclosure are shown in  FIG. 3 . As shown in  FIG. 3 , an exemplary method  300  comprises the step of introducing at least part of a detection device  202  into a luminal organ at a first location (introduction step  302 ), whereby detection device  202  comprises a detector  204 , and applying current to detection device  202  to allow detector  204  to operate (current application step  304 ). The application/excitation of current may be performed using a stimulator  218 . Method  300 , in at least one embodiment, further comprises the steps of introducing a first signal having a first frequency and a second signal having a second frequency through detection device  202  (frequency introduction step  306 ), and injecting a solution having a known conductivity into the luminal organ at or near detector  204  of detection device  202  (solution injection step  308 ). In an exemplary embodiment of a method  300  of the present disclosure, frequency introduction step  306  is performed using a frequency generator  206 . 
     After injection of the solution, exemplary method  300  further comprises the step of measuring an output conductance of the first signal and the second signal at the first location (conductance measurement step  310 ), and the step of calculating a parallel tissue conductance at the first location (calculation step  312 ), in an exemplary embodiment, based in part upon the output conductance and the conductivity of the injected solution. 
     Calculation step  312 , in at least one embodiment, may comprise the step of calculating a cross-sectional area of the luminal organ at the first location. In an exemplary embodiment wherein the first location comprises a plaque site, calculation step  312  may comprise the step of determining plaque-type composition of a plaque at the plaque site. 
     Conductance measurement step  310  may include the measurement of an output conductance whereby the output conductance comprises a first conductance value and a second conductance value. In at least one embodiment, the first conductance value corresponds to the first frequency and the second conductance value corresponds to the second frequency. In an exemplary embodiment, calculation step  312  may comprise the step of deconvoluting the output conductance to obtain a first conductance value and a second conductance value from the output conductance. In at least one embodiment, the step of deconvoluting the output conductance is performed using a deconvolution device  216 . 
     In at least one embodiment of a method  300  of the present disclosure, the output conductance comprises a mixed signal. In such an embodiment, calculation step  312  may further comprise the step of deconvoluting the mixed signal to obtain a first conductance value and a second conductance value from the mixed signal. 
     Frequency introduction step  306  may involve the introduction of signals having frequencies with various characteristics. For example, and in at least one embodiment, the first signal and the second signal may be repeatedly alternated to form a multiplexed signal. The alternated signals may then be separated in time by a short amount of time, for example 1 to 1000 milliseconds. In an exemplary embodiment, the first signal and the second signal are separated in time by less than 100 milliseconds. In another exemplary embodiment, the first signal and the second signal are separated in time by less than 10 milliseconds. Frequency introduction step  306  may also involve the introduction of signals whereby the first signal and the second signal are combined to form a combined signal. 
     In an exemplary embodiment of conductance measurement step  310  of an exemplary method  300  of the present disclosure, conductance measurement step  310  may be performed using an exemplary detection device  202 . In at least one embodiment of a detection device  202  used in connection with a method  300  of the present disclosure, detector  204  of detection device  202  comprises detection electrodes  26 ,  28  positioned in between excitation electrodes  25 ,  27 , wherein excitation electrodes  25 ,  27  are capable of producing an electrical field. 
     In at least another exemplary embodiment of a method  300  of the present disclosure, and as shown in  FIG. 4 , method  300  comprises introduction step  302 , current application step  304 , and frequency introduction step  306  as referenced above. This additional exemplary method  300  then comprises the step of measuring an output conductance of a first signal and a second signal at the first location (conductance measurement step  310 ), whereby conductance measurement step  310  involves, in such an embodiment, measuring a first output conductance at the first location within a luminal organ in connection with a fluid native to the first location, with the native fluid having a first conductivity. After the foregoing conductance measurement step  310  has been performed, solution injection step  308  may then be performed, followed by a second conductance measurement step  310 , whereby the second conductance measurement step  310  measures a second output conductance of the first signal and the second signal at the first location in connection with the injected solution. With this acquired information, an exemplary method  300  of the present disclosure may include the step of calculating a parallel tissue conductance at the first location (calculation step  312 ), in such an exemplary embodiment, based in part upon the second output conductance and the known conductivity of the injected solution. Calculation step  312 , in at least one embodiment, may also be performed, for example, based in part upon the first output conductance and the native conductivity of the native fluid in addition to the second output conductance and the known conductivity of the injected solution. 
     Various characteristics of the aforementioned signals, generating the same, conductance values, filtering, frequencies, output signals, etc., apply to any number of methods  300  referenced herein. For example, and as shown in  FIG. 4 , calculation step  312  of method  300  may comprise the step of deconvoluting the second output conductance to obtain a first resulting conductance value and a second resulting conductance value from the second output conductance as referenced above in connection with method  300  shown in  FIG. 3 . 
     In addition, calculation step  312 , in at least one embodiment, may comprise the step of calculating a cross-sectional area of the luminal organ at the first location. In an exemplary embodiment wherein the first location comprises a plaque site, calculation step  312  may comprise the step of determining plaque-type composition of a plaque at the plaque site. 
     To consider a method of measuring G p  and related impedance, which are used to determine CSA or evaluate the type and/or composition of a plaque, a number of approaches may be used. In one approach, luminal cross-sectional area is measured by introducing a catheter from an exteriorly accessible opening (e.g., mouth, nose or anus for GI applications; or e.g., mouth or nose for airway applications) into the hollow system or targeted luminal organ. In an exemplary approach, G p  is measured by introducing a catheter from an exteriorly accessible opening into the hollow system or targeted luminal organ. For cardiovascular applications, the catheter can be inserted into the organs in various ways, for example, similar to conventional angioplasty. In at least one embodiment, an 18 gauge needle is inserted into the femoral artery followed by an introducer, and a guide wire is then inserted into the introducer and advanced into the lumen of the femoral artery. A 4 or 5 Fr conductance catheter is then inserted into the femoral artery via wire and the wire is subsequently retracted. The catheter tip containing the conductance (excitation) electrodes can then be advanced to the region of interest by use of x-ray (using fluoroscopy, for example). In another approach, this methodology is used on small to medium size vessels, such as femoral, coronary, carotid, and iliac arteries, for example. 
     With respect to the solution injection, studies indicate that an infusion rate of approximately 1 ml/s for a five second interval is sufficient to displace the blood volume and results in a local pressure increase of less than 10 mmHg in the coronary artery. This pressure change depends on the injection rate, which should be comparable to the organ flow rate. In at least one approach, dextran, albumin or another large molecular weight molecule can be added to the solution (saline, for example) to maintain the colloid osmotic pressure of the solution to reduce or prevent fluid or ion exchange through the vessel wall. 
     In at least one approach, the saline solution is heated to body temperature prior to injection since the conductivity of current is temperature dependent. In another approach, the injected bolus is at room temperature, but a temperature correction is made since the conductivity is related to temperature in a linear fashion. 
     In an exemplary approach, a sheath is inserted either through the femoral or carotid artery in the direction of flow. To access the left anterior descending (LAD) artery, the sheath is inserted through the ascending aorta. For the carotid artery, where the diameter is typically on the order of 5.0-5.5 mm, a catheter having a diameter of 1.9 mm can be used. For the femoral and coronary arteries, where the diameter is typically in the range from 3.5-4.0 mm, a catheter of about 0.8 mm diameter would be appropriate. Such a device can be inserted into the femoral, carotid or LAD artery through a sheath appropriate for the particular treatment. Measurements for all three vessels can be similarly made. 
     The saline solution can be injected by hand or by using a mechanical injector to momentarily displace the entire volume of blood or bodily fluid in the vessel segment of interest. The pressure generated by the injection will not only displace the blood in the antegrade direction (in the direction of blood flow) but also in the retrograde direction (momentarily push the blood backwards). In other visceral organs that may be normally collapsed, the saline solution will not displace blood as in the vessels but will merely open the organs and create a flow of the fluid. 
     The injection described above may be repeated at least once to reduce errors associated with the administration of the injection, such as, for example, where the injection does not completely displace the blood or where there is significant mixing with blood. Bifurcation(s) (with branching angle near 90 degrees) near the targeted luminal organ may potentially cause an error in the calculated G p . Hence, generally the detection device should be slightly retracted or advanced and the measurement repeated. An additional application with multiple detection electrodes or a pull back or push forward during injection could accomplish the same goal. Here, an array of detection electrodes can be used to minimize or eliminate errors that would result from bifurcations or branching in the measurement or treatment site. 
     In an exemplary approach, error due to the eccentric position of the electrode or other imaging device can be reduced by inflation of a balloon on the device. The inflation of the balloon during measurement will place the electrodes or other imaging device in the center of the vessel away from the wall. In the case of impedance electrodes, the inflation of the balloon can be synchronized with the injection of bolus where the balloon inflation would immediately precede the bolus injection. 
     CSAs calculated in connection with the foregoing correspond to the area of the vessel or organ external to the device used (CSA of vessel minus CSA of the device). If the conductivity of the saline solution is determined by calibration with various tubes of known CSA, then the calibration accounts for the dimension of the device and the calculated CSA corresponds to that of the total vessel lumen as desired. In at least one embodiment, the calibration of the CSA measurement system will be performed at 37° C. by applying 100 mmHg in a solid polyphenolenoxide block with holes of known CSA ranging from 7.065 mm 2  (3 mm in diameter) to 1017 mm 2  (36 mm in diameter). If the conductivity of the solution(s) is/are obtained from a conductivity meter independent of the device, however, then the CSA of the device is generally added to the computed CSA to give the desired total CSA of the luminal organ. 
     The signals obtained herein are generally non-stationary, nonlinear and stochastic. To deal with non-stationary stochastic functions, one may use a number of methods, such as the Spectrogram, the Wavelet&#39;s analysis, the Wigner-Ville distribution, the Evolutionary Spectrum, Modal analysis, or preferably the intrinsic model function (IMF) method. The mean or peak-to-peak values can be systematically determined by the aforementioned signal analysis and used to compute the G p  as referenced herein. 
     Referring to the embodiment shown in  FIG. 5A , the angioplasty balloon  30  is selected on the basis of G p  and is shown distended within a coronary artery  150  for the treatment of stenosis. As described above with reference to  FIG. 2C , a set of excitation electrodes  40 ,  41  and detection electrodes  42 ,  43  are located within the angioplasty balloon  30 . In another embodiment, and as shown in  FIG. 5B , an angioplasty balloon  30  is used to distend a stent  160  within blood vessel  150 . 
     In an additional exemplary approach, concomitant with measuring G p  and or pressure gradient at the treatment or measurement site, a mechanical stimulus is introduced by way of inflating a low or high pressure balloon based on high or low value of G p , respectively. This action releases the stent from the device, thereby facilitating flow through the stenosed part of the organ. In another approach, concomitant with measuring G p  and or pressure gradient at the treatment site, one or more pharmaceutical substances for diagnosis or treatment of stenosis is injected into the treatment site. For example, an in at least one approach, the injected substance can be smooth muscle agonist or antagonist. In yet another approach, concomitant with measuring G p  and or pressure gradient at the treatment site, an inflating fluid is released into the treatment site for release of any stenosis or materials causing stenosis in the organ or treatment site. 
     For valve area determination, it is not generally feasible to displace the entire volume of the heart. Hence, the conductivity of blood is changed by injection of a hypertonic saline solution into the pulmonary artery which will transiently change the conductivity of blood. If the measured total conductance is plotted versus blood conductivity on a graph, the extrapolated conductance at zero conductivity corresponds to the parallel conductance. In order to ensure that the two inner electrodes of the detector are positioned in the plane of the valve annulus (2-3 mm), in one exemplary embodiment, two pressure sensors are advantageously placed immediately proximal and distal to the detection electrodes (1-2 mm above and below, respectively) or several sets of detection electrodes (see, e.g.,  FIGS. 2E and 2G ). The pressure readings will then indicate the position of the detection electrode relative to the desired site of measurement (aortic valve: aortic-ventricular pressure; mitral valve: left ventricular-atrial pressure; tricuspid valve: right atrial-ventricular pressure; pulmonary valve: right ventricular-pulmonary pressure). The parallel conductance at the site of annulus is generally expected to be small since the annulus consists primarily of collagen which has low electrical conductivity. In an additional application, a pull back or push forward through the heart chamber will show different conductance due to the change in geometry and parallel conductance. This can be established for normal patients which can then be used to diagnose valvular stenosis. 
     In an exemplary approach for the esophagus or the urethra, the procedures can conveniently be done by swallowing fluids of known conductances into the esophagus and infusion of fluids of known conductances into the urinary bladder followed by voiding the volume. In another approach, fluids can be swallowed or urine voided followed by measurement of the fluid conductances from samples of the fluid. The latter method can be applied to the ureter where a catheter can be advanced up into the ureter and fluids can either be injected from a proximal port on the probe (will also be applicable in the intestines) or urine production can be increased and samples taken distal in the ureter during passage of the bolus or from the urinary bladder. 
     In another exemplary approach, concomitant with measuring the cross-sectional area and or pressure gradient at the treatment or measurement site, a mechanical stimulus is introduced by way of inflating the balloon or by releasing a stent from the catheter, thereby facilitating flow through the stenosed part of the organ. In another approach, concomitant with measuring the cross-sectional area and or pressure gradient at the treatment site, one or more pharmaceutical substances for diagnosis or treatment of stenosis is injected into the treatment site. For example, in one approach, the injected substance can be smooth muscle agonist or antagonist. In yet another approach, concomitant with measuring the cross-sectional area and or pressure gradient at the treatment site, an inflating fluid is released into the treatment site for release of any stenosis or materials causing stenosis in the organ or treatment site. 
     Again, it is noted that the devices, systems, and methods described herein can be applied to any body lumen or treatment site. For example, the devices, systems, and methods described herein can be applied to any one of the following exemplary bodily hollow systems: the cardiovascular system including the heart, the digestive system, the respiratory system, the reproductive system, and the urogenital tract. 
     The various single injection methods  300  of the present disclosure offer a number of advantages over a two-injection method, including the reduction in the number of steps for the physician to perform (one injection instead of two), and the overall reduction in time to perform a procedure. Furthermore, a single injection method  300  allows a physician to obtain the CSA at the same time as opposed to matching between the two injections, which involves fewer assumptions and is therefore more accurate. A single injection method  300  also allows for the reconstruction of the temporal variation of the CSA during the injection period, allowing for a mean, minimum or maximum CSA to be determined. In addition to the foregoing, a single injection method  300  reduces the signal processing to identify the point of injection since there is only one injection, and it is easier to identify and match the simultaneous signals since the two frequency-conductance curves occur on the same time domain. Furthermore, the techniques of the present disclosure are minimally invasive, accurate, reliable and easily reproducible. 
     The use of multiple frequencies to determine the cross-sectional area (CSA) and parallel conductance (Gp) is discussed in detail within U.S. Patent Application Ser. No. 13/520,944 of Kassab. As noted therein, the relation between electrical conductance (G=I/V, where I and V are the current used and the voltage drop measured, respectively, and where G is the total conductance) is provided as follows: 
     
       
         
           
             
               
                 
                   G 
                   = 
                   
                     
                       
                         σ 
                         L 
                       
                        
                       CSA 
                     
                     + 
                     Gp 
                   
                 
               
               
                 
                   [ 
                   18 
                   ] 
                 
               
             
           
         
       
     
     It is well known that muscle organs (e.g., heart) have a Log relation that depends on frequency (f) such that Equation [18] becomes frequency dependent: 
     
       
         
           
             
               
                 
                   
                     G 
                      
                     
                       ( 
                       f 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           σ 
                            
                           
                             ( 
                             f 
                             ) 
                           
                         
                         L 
                       
                        
                       CSA 
                     
                     + 
                     
                       a 
                        
                       
                           
                       
                        
                       
                         Log 
                          
                         
                           ( 
                           f 
                           ) 
                         
                       
                     
                     + 
                     b 
                   
                 
               
               
                 
                   [ 
                   19 
                   ] 
                 
               
             
           
         
       
     
     where f designates the frequency, CSA indicates the cross-sectional area, σ refers to the conductivity, is spacing length between detection electrodes, a and b are constant parameters, and Log indicates the logarithm in base  10 . In this formulation, estimating the parameters CSA, a and b for a given set of experimental data that provide G for different frequencies f would be desired. The present disclosure demonstrates that experimental data for three (3) independent frequencies would be sufficient to have a deterministic solution. An expression for the parameters as a function of these data points consistent with the foregoing is provided herein, which is also validated with a numerical example. 
     In the previous formulation, G is a linear function of CSA, a and thus data at three (3) independent frequencies would be sufficient to estimate them uniquely, assuming σ(f) is continuous. Indeed, for 3 such frequencies f 1 , f 2 , and f 3  we would have: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             σ 
                              
                             
                               ( 
                               
                                 f 
                                 1 
                               
                               ) 
                             
                           
                           L 
                         
                          
                         CSA 
                       
                       + 
                       
                         
                           Log 
                            
                           
                             ( 
                             
                               f 
                               1 
                             
                             ) 
                           
                         
                          
                         a 
                       
                       + 
                       b 
                     
                     = 
                     
                       G 
                        
                       
                         ( 
                         
                           f 
                           1 
                         
                         ) 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         
                           
                             σ 
                              
                             
                               ( 
                               
                                 f 
                                 2 
                               
                               ) 
                             
                           
                           L 
                         
                          
                         CSA 
                       
                       + 
                       
                         
                           Log 
                            
                           
                             ( 
                             
                               f 
                               2 
                             
                             ) 
                           
                         
                          
                         a 
                       
                       + 
                       b 
                     
                     = 
                     
                       G 
                        
                       
                         ( 
                         
                           f 
                           2 
                         
                         ) 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         
                           
                             σ 
                              
                             
                               ( 
                               
                                 f 
                                 3 
                               
                               ) 
                             
                           
                           L 
                         
                          
                         CSA 
                       
                       + 
                       
                         
                           Log 
                            
                           
                             ( 
                             
                               f 
                               3 
                             
                             ) 
                           
                         
                          
                         a 
                       
                       + 
                       b 
                     
                     = 
                     
                       G 
                        
                       
                         ( 
                         
                           f 
                           3 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   20 
                   ] 
                 
               
             
           
         
       
     
     Equation [20] could be written in matrix form as: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           [ 
                           
                             
                               
                                 
                                   
                                     σ 
                                      
                                     
                                       ( 
                                       
                                         f 
                                         1 
                                       
                                       ) 
                                     
                                   
                                   L 
                                 
                               
                               
                                 
                                   Log 
                                    
                                   
                                     ( 
                                     
                                       f 
                                       1 
                                     
                                     ) 
                                   
                                 
                               
                               
                                 1 
                               
                             
                             
                               
                                 
                                   
                                     σ 
                                      
                                     
                                       ( 
                                       
                                         f 
                                         2 
                                       
                                       ) 
                                     
                                   
                                   L 
                                 
                               
                               
                                 
                                   Log 
                                    
                                   
                                     ( 
                                     
                                       f 
                                       2 
                                     
                                     ) 
                                   
                                 
                               
                               
                                 1 
                               
                             
                             
                               
                                 
                                   
                                     σ 
                                      
                                     
                                       ( 
                                       
                                         f 
                                         3 
                                       
                                       ) 
                                     
                                   
                                   L 
                                 
                               
                               
                                 
                                   Log 
                                    
                                   
                                     ( 
                                     
                                       f 
                                       3 
                                     
                                     ) 
                                   
                                 
                               
                               
                                 1 
                               
                             
                           
                           ] 
                         
                          
                       
                       A 
                     
                      
                     
                       
                         
                           { 
                           
                             
                               
                                 CSA 
                               
                             
                             
                               
                                 a 
                               
                             
                             
                               
                                 b 
                               
                             
                           
                           } 
                         
                          
                       
                       X 
                     
                   
                   = 
                   
                     
                       
                         { 
                         
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                           
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     2 
                                   
                                   ) 
                                 
                               
                             
                           
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     3 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                         } 
                       
                        
                     
                     b 
                   
                 
               
               
                 
                   [ 
                   21 
                   ] 
                 
               
             
           
         
       
     
     We have a system of the form AX=g. Such a system would yield a unique solution vector X if and only if A is invertible, which would be the case if its determinant is non-zero. We have here: 
     
       
         
           
             
               
                 
                   
                     det 
                      
                     
                       ( 
                       a 
                       ) 
                     
                   
                   = 
                   
                     
                       1 
                       L 
                     
                      
                     
                       ( 
                       
                         
                           
                             Log 
                              
                             
                               ( 
                               
                                 f 
                                 1 
                               
                               ) 
                             
                           
                            
                           
                             ( 
                             
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     3 
                                   
                                   ) 
                                 
                               
                               - 
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     2 
                                   
                                   ) 
                                 
                               
                             
                             ) 
                           
                         
                         + 
                         
                           
                             Log 
                              
                             
                               ( 
                               
                                 f 
                                 2 
                               
                               ) 
                             
                           
                            
                           
                             ( 
                             
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     1 
                                   
                                   ) 
                                 
                               
                               - 
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     3 
                                   
                                   ) 
                                 
                               
                             
                             ) 
                           
                         
                         + 
                         
                           
                             Log 
                              
                             
                               ( 
                               
                                 f 
                                 3 
                               
                               ) 
                             
                           
                            
                           
                             ( 
                             
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     2 
                                   
                                   ) 
                                 
                               
                               - 
                               
                                 σ 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   22 
                   ] 
                 
               
             
           
         
       
     
     If the frequencies f 1  are independent, the determinant of A would clearly be non-zero. Thus, by inverting A we have: 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       { 
                       
                         
                           
                             CSA 
                           
                         
                         
                           
                             a 
                           
                         
                         
                           
                             b 
                           
                         
                       
                       } 
                     
                     = 
                     
                       
                         1 
                         
                           det 
                            
                           
                             ( 
                             A 
                             ) 
                           
                         
                       
                        
                       B 
                        
                       
                         { 
                         
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                           
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     2 
                                   
                                   ) 
                                 
                               
                             
                           
                           
                             
                               
                                 G 
                                  
                                 
                                   ( 
                                   
                                     f 
                                     3 
                                   
                                   ) 
                                 
                               
                             
                           
                         
                         } 
                       
                        
                       
                           
                       
                        
                       with 
                     
                   
                 
               
               
                 
                   [ 
                   23 
                   ] 
                 
               
             
             
               
                 
                   B 
                   = 
                   
                     [ 
                     
                       
                         
                           
                             
                               Log 
                                
                               
                                 ( 
                                 
                                   f 
                                   2 
                                 
                                 ) 
                               
                             
                             - 
                             
                               Log 
                                
                               
                                 ( 
                                 
                                   f 
                                   3 
                                 
                                 ) 
                               
                             
                           
                         
                         
                           
                             
                               Log 
                                
                               
                                 ( 
                                 
                                   f 
                                   2 
                                 
                                 ) 
                               
                             
                             - 
                             
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                                 ( 
                                 
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                                 ) 
                               
                             
                           
                         
                         
                           
                             
                               Log 
                                
                               
                                 ( 
                                 
                                   f 
                                   1 
                                 
                                 ) 
                               
                             
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                                 ( 
                                 
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                                   ( 
                                   
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                               - 
                               
                                 σ 
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                                   ( 
                                   
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                             L 
                           
                         
                         
                           
                             
                               
                                 σ 
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                                   ( 
                                   
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                                   ( 
                                   
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                                           ( 
                                           
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                                           ) 
                                         
                                       
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                                           ( 
                                           
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                                           ) 
                                         
                                       
                                     
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                                         ( 
                                         
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                                       σ 
                                        
                                       
                                         ( 
                                         
                                           f 
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                                         ) 
                                       
                                     
                                   
                                 
                               
                             
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                                           ( 
                                           
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                                           ) 
                                         
                                       
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                                           ( 
                                           
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                                           ) 
                                         
                                       
                                     
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                                         ( 
                                         
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                                         ( 
                                         
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                                         ) 
                                       
                                     
                                   
                                 
                               
                             
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                                           ( 
                                           
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                                           ) 
                                         
                                       
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                                           ( 
                                           
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                                           ) 
                                         
                                       
                                     
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                                         ( 
                                         
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                                           2 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             L 
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   [ 
                   24 
                   ] 
                 
               
             
           
         
       
     
     This formulation could be used to estimate CSA, a and b for a given set of experimental data (f 1 , G(f 1 )), (f 2 , G(f 2 )), (f 3 , g(f 3 )). 
     The formulations derived above are validated through the following example. To demonstrate the same, a reverse problem is constructed. For example, assume that CSA 1 =0.02, a 1 =2, and b 1 =3 (known data), and also consider an exponential decay behavior for the conductivity σ 1 (f)=10 4 e −f/2000 , and L 1 −1. The corresponding conductance function is given by: 
     
       
         
           
             
               
                 
                   
                     
                       G 
                       1 
                     
                      
                     
                       ( 
                       f 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             σ 
                             1 
                           
                            
                           
                             ( 
                             f 
                             ) 
                           
                         
                         
                           L 
                           1 
                         
                       
                        
                       
                         CSA 
                         1 
                       
                     
                     + 
                     
                       
                         Log 
                          
                         
                           ( 
                           f 
                           ) 
                         
                       
                        
                       
                         a 
                         1 
                       
                     
                     + 
                     
                       b 
                       1 
                     
                   
                 
               
               
                 
                   [ 
                   25 
                   ] 
                 
               
             
           
         
       
     
     For three (3) frequencies (f 1 , f 2 , f 3 )=(100, 1000, 10000), the corresponding conductance values are (G 1 (f 1 ), G 2 (f 2 ), G 3 (f 3 )=(31.2349, 28.9461, 21.5554). 
     We can then assume that we have obtained experimentally the previous set of data (f 1 , G 1 (f 1 )), (f 2 , G 1 (f 2 )), f 3 , G 1 (f 3 )) for validation discussion purposes. We can then verify that we can determine CSA 1 , a 1 , and b 1  using the expressions from Equations [23] and [24], as noted by: 
     
       
         
           
             
               
                 
                   
                     { 
                     
                       
                         
                           CSA 
                         
                       
                       
                         
                           a 
                         
                       
                       
                         
                           b 
                         
                       
                     
                     } 
                   
                   = 
                   
                     
                       
                         1 
                         5873.76 
                       
                        
                       
                         [ 
                         
                           
                             
                               
                                 - 
                                 2.30259 
                               
                             
                             
                               4.60517 
                             
                             
                               
                                 - 
                                 2.30259 
                               
                             
                           
                           
                             
                               
                                 - 
                                 5997.93 
                               
                             
                             
                               9444.91 
                             
                             
                               
                                 - 
                                 3446.99 
                               
                             
                           
                           
                             
                               55398.1 
                             
                             
                               
                                 - 
                                 87301.2 
                               
                             
                             
                               37776.8 
                             
                           
                         
                         ] 
                       
                     
                      
                     
                       { 
                       
                         
                           
                             31.2349 
                           
                         
                         
                           
                             
                               28.9461 
                               ) 
                             
                           
                         
                         
                           
                             21.5554 
                           
                         
                       
                       } 
                     
                      
                     
                         
                     
                      
                     and 
                   
                 
               
               
                 
                   [ 
                   26 
                   ] 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     
                       { 
                       
                         
                           
                             CSA 
                           
                         
                         
                           
                             a 
                           
                         
                         
                           
                             b 
                           
                         
                       
                       } 
                     
                     - 
                     
                       { 
                       
                         
                           
                             
                               0.02 
                               ) 
                             
                           
                         
                         
                           
                             2 
                           
                         
                         
                           
                             3 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   [ 
                   27 
                   ] 
                 
               
             
           
         
       
     
     The initial parameters which validates the formulation and the statement that data at three (3) independent frequencies are sufficient to estimate the required parameters are therefore verified. 
     In an alternative embodiment where additional frequencies are sought to create redundancies in equations, more equations (&gt;3) can be obtained than the three unknowns. In such an approach, for example, a linear least squares fit of the data can be used to determine the average values of CSA, a and b. 
     The aforementioned methodology is beneficial as current technology generally requires at least one injection, such as an injection of a quantity of saline, in connection with obtaining conductance measurements using impedance by way of an impedance device having a detector (excitation and detection electrode(s)) thereupon, such as referenced within U.S. patent application Ser. No. 13/520,944 of Kassab. By instead using three different frequencies through said detector, an accurate and actual CSA measurement of a luminal organ can be obtained using such a device without requiring any sort of saline or other injections. As referenced herein, devices of the present disclosure are configured to obtain conductance data within a mammalian luminal organ in connection with three signals having different frequencies (which can be, for example, a mixed signal having the three signals), wherein the conductance data is sufficient for use to determine a cross-sectional area within the mammalian luminal organ by calculating the cross-sectional area using the conductance data, a conductivity of blood within the mammalian luminal organ, and a known distance between detection elements of an impedance detector of the device. Said devices are therefore operable and configured to obtain said data in the presence of a native fluid within a luminal organ, such as blood, and obtain said data without requiring or in the presence of any sort of fluid injection. 
     While various embodiments of methods for determining cross-sectional areas using multiple frequencies and without requiring fluid injections have been described in considerable detail herein, the embodiments are merely offered as non-limiting examples of the disclosure described herein. It will therefore be understood that various changes and modifications may be made, and equivalents may be substituted for elements thereof, without departing from the scope of the present disclosure. The present disclosure is not intended to be exhaustive or limiting with respect to the content thereof. 
     Further, in describing representative embodiments, the present disclosure may have presented a method and/or a process as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth therein, the method or process should not be limited to the particular sequence of steps described, as other sequences of steps may be possible. Therefore, the particular order of the steps disclosed herein should not be construed as limitations of the present disclosure. In addition, disclosure directed to a method and/or process should not be limited to the performance of their steps in the order written. Such sequences may be varied and still remain within the scope of the present disclosure.