Abstract:
A method and device for sensing the temperature profile of a hollow body organ includes a catheter and a hollow guidewire carrying a thermal sensor. The guidewire is configured to displace the thermal sensor radially relative to the catheter when unconstrained and can be rotated about the longitudinal axis of the catheter. When constrained within the catheter, the guidewire can be advanced to a region of interest in hollow body organ. The catheter can be withdrawn, leaving the guidewire in place in an expanded configuration wherein the thermal sensor contacts the inner wall of the hollow body organ. The guidewire is moveable to sense the temperature at multiple locations. The thermal sensor can be replaced with an electrode for sensing the impedance profile of the hollow body organ.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/904,212 filed Jul. 12, 2001 (now abandoned) and is a continuation-in-part of U.S. patent application Ser. No. 09/904,024 also filed Jul. 12, 2001 (now abandoned), each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to invasive medical devices and more particularly to methods and devices for sensing and mapping the temperature of the interior wall of a hollow body organ such as a blood vessel. 
     BACKGROUND OF THE INVENTION 
     Acute ischemic syndromes involving arterial blood vessels, such as myocardial infarction, or heart attack, and stroke, frequently occur when atherosclerotic plaque ruptures, triggering the formation of blood clots, or thrombosis. Plaque that is inflamed is particularly unstable and vulnerable to disruption, with potentially devastating consequences. Therefore, there is a strong need to detect and locate this type of plaque so that treatment can be initiated before the plaque undergoes disruption and induces subsequent life-threatening clotting. 
     Various procedures are known for detecting and locating plaque in a blood vessel. Angiography is one such procedure in which X-ray images of blood vessels are generated after a radiopaque dye is injected into the blood stream. This procedure is capable of locating plaque in an artery, but is not capable of revealing whether the plaque is the inflamed, unstable type. 
     Researchers, acting on the theory that inflammation is a factor in the development of atherosclerosis, have discovered that local variations of temperature along arterial walls can indicate the presence of inflamed plaque. The temperature at the site of inflamation, i.e., the unstable plaque, is elevated relative to adjacent plaque-free arterial walls. 
     Using a tiny thermal sensor at the end of a catheter, the temperature at multiple locations along an arterial wall were measured in people with and without atherosclerotic arteries. In people free of heart disease, the temperature was substantially homogeneous wherever measured: an average of 0.65 degrees F. above the oral temperature. In people with stable angina, the temperature of their plaques averaged 0.19 degrees F. above the temperature of their unaffected artery walls. The average temperature increase in people with unstable angina was 1.23 degrees F. The increase was 2.65 degrees F. in people who had just suffered a heart attack. Furthermore, temperature variation at different points at the plaque site itself was found to be greatest in people who had just had a heart attack. There was progressively less variation in people with unstable angina and stable angina. 
     The temperature heterogeneity discussed above can be exploited to detect and locate inflamed, unstable plaque through the use of cavity wall profiling apparatus. Typically, cavity wall profiling apparatus are comprised of temperature indicating probes such as thermocouples, thermistors, fluorescence lifetime measurement systems, resistance thermal devices and infrared measurement devices. 
     One problem with conventional cavity wall profiling apparatus is that they usually exert an undue amount of force on the region of interest. If the region of interest cannot withstand these forces, it may be damaged. The inside walls of a healthy human artery are vulnerable to such damage. Furthermore, if inflamed, unstable plaque is present it may be ruptured by such forces. 
     Another problem with conventional cavity wall profiling apparatus is that they can only measure the temperature at one specific location. In order to generate a map of the cavity temperature variation, one would need to move the temperature indicating probe from location to location. This can be very tedious, can increase the risk of damaging the vessel wall or rupturing vulnerable plaque, and may not resolve temporal characteristics of the profile with sufficient resolution. An array of probes could be employed but that could be very big and heavy. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a device is provided for sensing the temperature profile of a hollow body organ. The device includes a catheter, a hollow guidewire, and a temperature sensor disposed on or within the guidewire. The guidewire has a relaxed configuration externally of the catheter that is formed to provide contact with the wall of the hollow body organ. The guidewire also has a contracted configuration internally of the catheter and is of a lesser diameter than the catheter. 
     According to another aspect of the invention, a method for sensing and mapping the temperature profile of a hollow body organ utilizes a catheter, a guidewire, and a thermal sensor disposed on or within the guidewire. The guidewire has a relaxed configuration externally of the catheter that is formed to provide contact with the wall of the hollow body organ. The guidewire also has a contracted configuration internally of the catheter and is of a lesser diameter than the catheter. 
     The device is used by contracting the guidewire elastically and constraining the guidewire within the catheter. The catheter and guidewire are advanced to a region of interest in a hollow body organ. The catheter is withdrawn to expose the distal portion of the guidewire in a relaxed configuration in contact with the hollow body organ. The guidewire is moved longitudinally and rotated, continuously or continually, to sense the temperature of the hollow body organ at multiple locations. 
     Further aspects and advantages of the present invention are apparent from the following description of a preferred embodiment referring to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is a perspective view of a preferred embodiment of the present invention; 
         FIG. 2  is a longitudinal sectional view of an arterial hollow body organ in which the embodiment of  FIG. 1 , also shown in longitudinal section, is deployed; 
         FIG. 3  is a longitudinal sectional view of an arterial hollow body organ in which another preferred embodiment of the present invention, also shown in longitudinal section, is deployed; 
         FIG. 4  is a perspective view of yet another preferred embodiment of the present invention; 
         FIG. 5  is a perspective view, partially in section, of a further preferred embodiment of the present invention; 
         FIG. 6  is a perspective view of yet another preferred embodiment of the present invention; 
         FIG. 7  is a longitudinal sectional view of an arterial hollow body organ in which another preferred embodiment of the present invention, shown in perspective, is deployed; 
         FIG. 8  is a perspective view of a further preferred embodiment of the present invention; 
         FIG. 9  is a perspective view of another preferred embodiment of the present invention; and 
         FIG. 10  is a longitudinal sectional view of an arterial hollow body organ in which yet another preferred embodiment of the present invention, shown in perspective, is deployed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a device  10  for profiling the wall of a hollow body organ device  10  includes a lumened catheter  12  having a central lumen  14 , a hollow guidewire  16  that defines a conduit comprising a tubular helix formed of metal wire  18  or the like in the shape of a coil defining a central lumen (not shown), and a thermal sensor  20  disposed at the terminal end of the distal portion of guidewire  16 . Conventional conductors or other signal carrying structures (not shown) are provided to convey signals from the thermal sensor  20  along guidewire  16  and out of the proximal portion of guidewire  16  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. Thermal sensor  20  can be a thermocouple, a thermistor, or an infrared radiation sensor, for example, and is secured by appropriate mechanical or adhesive means to the terminal end of guidewire  16 . 
     Hollow guidewire  16  is made of thin wire  18  wound, for example around a mandrel, into small helical coils of desired diameter that lie tightly adjacent one another to form a hollow tube having a central passageway or lumen therethrough. Guidewire  16  has an outer diameter somewhat less than the inner diameter of catheter  12  to permit guidewire  16  to slide freely within the lumen  14  of catheter  12 . In addition, guidewire  16 , in its relaxed configuration, is shaped in the form of a bend  22  at the distal portion thereof, the bend  22  being spaced from the terminal end of guidewire  16  at which thermal sensor  20  is disposed. Consequently, thermal sensor  20  is displaced radially from the longitudinal axis  24  of guidewire  16  and catheter  12  when guidewire  16  is in the relaxed, bent configuration. Through external manipulation, guidewire  16  in the relaxed, bent configuration can be made to rotate about axis  24 , continuously or continually, depending on the response time for the sensor, thereby causing thermal sensor  20  to traverse a circumferential or helical path about axis  24  while providing temperature information. Guidewire  16  can be deformed elastically into a substantially straight configuration, i.e., without bend  22 , under force. When the force is removed, guidewire  16  returns to the relaxed, bent configuration. 
     Guidewire  16  can be constructed of spring steel that can be deformed into a relatively straight configuration when withdrawn into catheter  12 , but which springs back to its bent configuration when extruded from catheter  12  and released from constraint. Another way is to construct guidewire  16  of superelastic Nitinol and take advantage of the martensitic transformation properties of Nitinol. Guidewire  16  can be inserted into catheter  12  in its straight form and kept cool within the catheter by the injection of cold saline through catheter  12  and over guidewire  16 . Upon release of guidewire  16  into the bloodstream, it will warm up and change to its austenite memory shape based on the well-known martensitic transformation by application of heat and putting the material through its transformation temperature. 
     Guidewire  16  can also be made out of a composite such as a Nitinol tube within the guidewire structure. In this fashion, the martensitic or superelastic properties of Nitinol can be combined with the spring steel characteristics of the spring and lead to a desirable composition. Other suitable materials for guidewire  16  include copper, constantin, chromel or alumel. 
       FIG. 2  shows device  10  deployed in a hollow body organ comprising an arterial blood vessel  26  having an endothelium  28  forming the inner wall thereof. Only the distal portion of guidewire  16  that extends beyond catheter  12  is shown. Electrical conductor  32  extends through lumen  30  of guidewire  16 . Conductor  32  is electrically insulated from the coils  18  of guidewire  16  so that guidewire  16  comprises one conductor and conductor  32  comprises another conductor or lead of the thermal sensor  20  which can be thermocouple or thermistor. The conductors conveys signals from the thermal sensor  20  to the proximal end of guidewire  16  for connection to appropriate signal processing apparatus that converts the received signals to a temperature indication. 
     In use, the guidewire  16  and thermal sensor  20  of the preferred embodiment of device  10 , as shown in  FIGS. 1 and 2 , are inserted into the lumen  14  of catheter  12  from the proximal end. thereby constraining guidewire  16  in a substantially straight configuration with the thermal sensor  20  near the distal end of catheter  12 . Using conventional percutaneous insertion techniques, access to the blood vessel  26  is obtained surgically. Catheter  12 , with guidewire  16  and thermal sensor  20  disposed within, is advanced through the blood vessel  26  to the region of interest. 
     Catheter  12  is slowly withdrawn while guidewire  16  is secured against movement relative to the patient such that guidewire  16  emerges from the distal end of catheter  12  and reverts to the relaxed, bent configuration within the blood vessel  26 . Guidewire  16  remains substantially fixed in the axial direction relative to the blood vessel  26  as catheter  12  is withdrawn, with the re-formed bent distal portion of guidewire  16  springing gently radially outwardly into contact with the vessel wall  28 . 
     With guidewire  16  exposed and thermal sensor  20  lying in contact with the wall  28  of blood vessel  26 , the thermal sensor  20  senses the localized temperature of the vessel wall  28  at the region where the thermal sensor  20  is situated. By slowly withdrawing guidewire  16  into catheter  12  while simultaneously rotating guidewire  16  about its longitudinal axis, thermal sensor  20  can be made to traverse a helical path around the inner wall  28  of the blood vessel  26 , permitting temperature measurements to be taken at intervals of different regions of the vessel wall  28 . Depending upon the response time of thermal sensor  20 , rotation can be intermittent or continuous, as needed. By withdrawing and rotating the guidewire  16  at constant rates, the location of the thermal sensor  20  relative to the distal end of the catheter  12  can be determined as a function of time, so that a temperature profile of the blood vessel  26  can be mapped, provided the response time of the thermal sensor is relatively short. 
     Once the mapping is completed, the guidewire  16  is withdrawn fully into catheter  12 , re-sheathed and constrained in a substantially straight configuration. Catheter  12  can then either be withdrawn from the blood vessel  26  or repositioned to another region of interest within the hollow body organ for further mapping of the temperature profile at that region. 
       FIG. 3  shows a second preferred embodiment of a device  10 ′ for profiling the wall of a hollow body organ. Device  10 ′ can be deployed in a hollow body organ in a manner similar to the embodiment of device  10  shown in  FIGS. 1 and 2  and described above with respect to structure and use. Components of device  10 ′ that are similar in structure and function to corresponding components of device  10  of  FIGS. 1 and 2  are designated by like prime numerals. The description of device  10  above applies also to device  10 ′ unless described otherwise below. 
     Device  10 ′ includes a second thermal sensor  36  disposed at the outside of bend  22 ′ and exposed for contact with the inner wall  28 ′ of vessel  26 ′. A second electrical conductor  38  is electrically insulated from the conductor  32 ′ and from the wire  18 ′ of guidewire  16 ′ so that guidewire  16 ′ comprises one conductor and conductor  38  comprises another conductor of the thermocouple or thermistor of thermal sensor  36  for conveying signals from the thermal sensor  36  to the proximal end of guidewire  16  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. Wire  18 ′ of guidewire  16 ′ is a conductor common to thermal sensors  20 ′ and  36 . 
     Device  10 ′ of  FIG. 3  can be used in a manner substantially similar to the manner of use described above with respect to device  10  of  FIGS. 1 and 2 , except that thermistors  20 ′ and  36  simultaneously traverse intertwined helical paths in contact with the inner wall  28 ′ of hollow body organ  26 ′. Consequently, the temperature profile of the inner wall  28 ′ can be mapped more quickly because data can be gathered from different locations simultaneously. 
       FIG. 4  shows yet another preferred embodiment of a device  210  for profiling the wall temperature of a hollow body organ. Device  210  can be deployed in a hollow body organ in the manner described above with respect to the embodiments of devices  10  and  10 ′ shown in  FIGS. 1 ,  2  and  3  and described above. Components of device  210  that are similar in structure and function to corresponding components of device  10  of  FIGS. 1 and 2  are designated by like reference numerals in the  200  series but having the same last two digits. The description of device  10  above applies also to device  210  unless described otherwise below. 
     Device  210  of  FIG. 4  includes one thermal sensor  40  disposed at the outside of a dogleg bend  42  that is spaced distally from bend  222  and proximally from the terminal end of guidewire  216 . Thermal sensor  40  is exposed for contact with the inner wall  228  of vessel  226 . An electrical conductor (not shown) is electrically insulated from the wire  218  of guidewire  216  so that guidewire  216  comprises one conductor and the electrical conductor comprises another conductor of the thermocouple or thermistor of thermal sensor  40  for conveying signals from the thermal sensor  40  to the proximal end of guidewire  216  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. Unlike the embodiments of devices  10  and  10 ′ of  FIGS. 1 ,  2  and  3 , device  210  includes only a thermistor at dog-leg bend  42  and no thermistor at the terminal end of guidewire  216  or at bend  222 . 
     Device  210  of  FIG. 4  can be used in a manner substantially similar to the manner of use described above with respect to device  10  of  FIGS. 1 and 2 . 
       FIG. 5  shows a further preferred embodiment of a device  310  for profiling the wall temperature of a hollow body organ. Device  310  can be deployed in a hollow body organ in the manner described above with respect to the embodiments of device  10  shown in  FIGS. 1 and 2  and described above. Components of device  310  that are similar in structure and function to corresponding components of device  10  of  FIGS. 1 and 2  are designated by like reference numerals in the  300  series but having the same last two digits. The description of device  10  above applies also to device  310  unless described otherwise below. 
     Device  310  of  FIG. 5 , rather than having externally exposed thermal sensors as in the embodiments of  FIGS. 1 through 4  above, includes a thermal sensor  50  disposed within the lumen  330  of hollow guidewire  316  and in thermal contact with the coiled wire  318  that comprises guidewire  316 . Thermal sensor  50  is located at a dogleg bend  52  that is spaced between bend  322  and the distal end of guidewire  316 . Guidewire  316  also includes bend  54  between bend  52  and the distal end of guidewire  316 . Bends  322 ,  52  and  54  together cause the distal portion of guidewire  316  to assume the shape of a question mark when in a relaxed configuration. In such a configuration, bend  52  and bend  54  contact opposite sides of the inner wall of the hollow body organ. The spring nature of guidewire  316  urges bend  52  in contact with the hollow body organ. Insulated electrical conductors  56  and  58  are operatively connected to the thermocouple or thermistor of thermal sensor  50  for conveying signals from the thermal sensor  50  to the proximal end of guidewire  316  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. 
     Device  310  of  FIG. 5  can be used in a manner substantially similar to the manner of use described above with respect to device  10  of  FIGS. 1 and 2 . 
       FIG. 6  shows another embodiment of a device  410  for profiling the wall temperature of a hollow body organ. Device  410  is an alternative configuration of the device  310  of  FIG. 5 , in which bend  454  extends in a direction opposite to that of bend  54 , such that the terminal end portion of guidewire  416  extends axially away from catheter  412 . Bend  454  serves a purpose similar to that of bend  54  of device  310  of  FIG. 5 , i.e., to assure that bend  452 , at which thermal sensor  450  is located, remains in contact with the inner wall of the hollow body organ when deployed therein. 
       FIG. 7  shows yet another embodiment of the present invention. Temperature sensing device  510  is carried by hollow guidewire  516  which extends outwardly from the distal end of catheter  512  and includes thermal sensor  550 , e.g., a thermistor at a dogleg bend  552  spaced from bend  522  which is situated between the sensor-carrying bend  552  and the distal end portion of catheter  512 . The distal end portion of guide wire  516  terminates in a generally crescent-shaped loop and is rotatable, continuously or continually, as desired, to sense the temperature of the endothelium  528  lining the wall of blood vessel  526  in the vicinity of plaque deposit  592 . 
       FIG. 8  shows yet a further embodiment of a device  610  for profiling the wall temperature of a hollow body organ. Device  610  comprises another alternative configuration of the device  310  of  FIG. 5 , in which guidewire  616  is shaped as a plurality of loops  60  with a plurality of thermal sensors  62  located within guidewire  616  at each location along the loops  60  that would contact the wall of the hollow body organ when disposed therein. 
       FIG. 9  shows yet another embodiment of a device  710  for profiling the wall temperature of a hollow body organ. Device  710  includes a lumened catheter  712  and a hollow guidewire  716 . The inner surface of lumen  730  of guidewire  716 , at a bend  742  similar to bend  42  of device  210  of  FIG. 4 , is lined with a layer of black paint  70  which is in turn lined with a thermochromic material  72  that is sensitive to a change of temperature of the guidewire  716 . The color of the thermochromic material  72  varies as a function of temperature. 
     Disposed within lumen  730  of guidewire  716 , inwardly of thermochromic material  72 , is an optical probe  74  including an illuminating optical fiber  76  having a radially emitting diffuser  78  at the distal end thereof, and a sensing optical fiber  80  having a conically beveled distal end  82  for collecting light. An illuminating electromagnetic radiation source connected to the proximal end of illuminating optical fiber  76  provides illuminating radiation that is guided by optical fiber  76  to the region of interest within the hollow body organ, and diffused radially by diffuser  78  to illuminate the interior of lumen  730 , particularly thermochromic material  72 . The illuminating radiation can be in the visible, infrared or ultraviolet portions of the spectrum. Radiation from diffuser  78  is differentially absorbed and reflected by thermochromic material  72 , according to the color of material  72  which is indicative of the temperature of guidewire  716  in contact with the wall of the hollow body organ in the region of interest. 
     The light reflected from thermochromic material  72 , having wavelengths indicative of the color thereof, is collected by distal end  82  and directed toward the proximal end of sensing optical fiber  80 . An appropriate optical reflectance spectrometry device connected to the proximal end of sensing optical fiber  80  generates an electrical signal indicative of the color, and therefore temperature, of thermochromic material  72 . 
       FIG. 10  shows yet another embodiment of a device  810  suitable for profiling the impedance of the wall of a hollow body organ. Device  810  includes a catheter  812  within which is disposed a guidewire  816  having a dog-leg bend in the distal portion thereof. Device  810  is similar in configuration to the embodiment of device  210  of  FIG. 4 , and like components are indicated by like reference numerals in the  800  series but having the same last two digits. Unlike device  210  of  FIG. 4 , device  810  does not employ thermal sensing, but rather employs impedance sensing for profiling the wall of a hollow body organ. An electrode  90  at the outside of the dog-leg bend of guidewire  816  is in electrical contact with guidewire  816  and in electrical contact with the inner wall  828  of the hollow body organ  826 . Guidewire  816  comprises a conductor operatively connected to an external impedance measuring device that has a ground terminal electrically connected to the body in which the hollow body organ is located. A small electrical current is applied via guidewire  816  and electrode  90  to the inner wall  828  at the region of contact therebetween. The impedance of the electrical path through the body, including through the region of interest in the hollow body organ  826 , can be measured and recorded. By moving guidewire  816  relative to the hollow body organ  826  as described above with respect to other embodiments, the impedance of the wall of the vessel  826  can be mapped. Any change of impedance along the wall  828  indicates the presence of an anomaly in the wall, such as a plaque  92 . 
     Although the present invention has been described in detail in terms of preferred embodiments, no limitation on the scope of the invention is intended. The scope of the subject matter in which an exclusive right is claimed is defined in the appended claims.