Abstract:
A system and method for determining a pH level of blood in a vessel of a patient including a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, a sensor positioned at the distal portion of the elongated member, and a connector connecting the elongated member to an indicator. The sensor measures the pH level of blood downstream of the blood clot. A system and method are also provided for determining a density of a blood clot in a vessel of a patient for subsequent selection of a treatment method. The system includes a sensor positioned at the distal portion of the elongated member, and a connector connecting the elongated member to an indicator, wherein the sensor determines the density of the blood clot and the indicator provides an indication of the density of the clot.

Description:
[0001]    This application claims priority from provisional application Ser. No. 61/718,107, filed Oct. 24, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
     Technical Field 
       [0002]    This application relates to a system for determining the health of the vasculature to enable the surgeon to assess the advisability of blood clot removal. This application also relates to a system for identifying the composition of a blood clot in a vessel to enable the physician to scientifically determine the clot makeup to determine the best course of treatment for the clot. 
       Background of Related Art 
       [0003]    Cerebrovascular disease refers to diseases of the brain caused by vascular abnormalities which result in abnormal cerebral blood flow. The most common cause of cerebrovascular disease is narrowing of the major arteries supplying blood to the brain, resulting in thrombogenic disease or sudden occlusion of blood flow, which if large enough results in ischemic stroke. 
         [0004]    Clots (Ischemic Stroke) can originate in various areas and be caused by different modalities. These different modalities create clots that vary in consistency. The clot can be platelet rich (runny) or fibrin rich (hard) or anywhere in between the two. Ischemic stroke is caused by the thrombosis of a major vessel supplying blood to a region of the brain. A shortage of blood in the cerebral tissue leads to the deletion of metabolites such as oxygen and glucose, which in turn causes depletion of energy stores of the cells. Therefore, it is critical to remove the clots to restore adequate blood supply to the brain. 
         [0005]    Current treatments for clot removal include mechanical thrombectomy devices and application of thrombolytic drugs to dissolve the clot. A problem encountered with these approaches is that the composition of the clot is undetectable in situ, while the efficacy of these approaches is dependent in part on the clot composition. Therefore, the physician is taking one of the known approaches for treatment of the clot without the knowledge of the clot makeup, e.g., its consistency. This can lead to inconsistent results as well as failure to properly treat the clot. 
         [0006]    It would therefore be beneficial if the surgeon could identify the type of clot beforehand to better assess how the clot could be treated. Such prior knowledge would greatly enhance clot removal as the surgeon can adapt the approach to better match the treatment device or drugs with the type of clot. 
         [0007]    In addition, in cerebrovascular disease, the vitality of the vasculature distal to the clot is compromised once the clot lodges in place. Vasculature that has been deprived of oxygenated blood will necrose and become friable. Once blood flow is restored after clot removal, such blood flow could potentially cause a hemorrhagic event, which means the vessel can bleed out and burst open. Currently, surgeons do not have adequate knowledge of the vasculature downstream of the clot and therefore cannot accurately assess the risk of clot removal. 
         [0008]    It would be beneficial if the surgeon could determine the health of the vasculature distal to the clot prior to removal of the clot so the surgeon could determine if clot removal is advisable and/or take necessary precautions during clot removal so the vessels are not compromised. Prior attempts to measure pH using magnetic resonance imaging (MRI) technique have been attempted, as explained for example in “Modelling of pH Dynamics in Brain Cells After Stroke”, by Piotr Orlowski, et al., published in Interface Focus, The Royal Society, 2011. However, these attempts to date have been unsuccessful. Additionally, relying on MRI is very expensive and requires relatively complex mathematical models. Therefore, although the role of pH is recognized, the need exists to utilize this parameter to readily determine vascular tissue health to enhance blood clot removal or prevent clot removal where the risk is too great. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a system and method for assessing vasculature downstream of the clot and a system and method for assessing the blood clot. The two systems can be used independently, or alternatively, can be used together as either separate systems or a single (combined) system. 
         [0010]    In one aspect, the present invention provides a system for determining a pH level of blood in a vessel of a patient. The system comprises a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, the elongated member having a proximal portion and a distal portion and configured for insertion so the distal portion extends past a blood clot for positioning of the distal portion distal of the blood clot. A sensor is positioned at the distal portion of the elongated member for positioning distal of the blood clot. A connector connects the elongated member to an indicator, the sensor measuring the pH level of blood, preferably in a closed or a substantially closed system downstream of the blood clot, to thereby determine pH of the vessel downstream of the blood clot to determine the condition of the vessel to assess subsequent treatment of the blood clot. The indicator provides an indication of the blood pH measured by the sensor. 
         [0011]    In one embodiment, the flexible elongated member comprises a catheter. In another embodiment, the flexible elongated member comprises a guidewire. 
         [0012]    In one embodiment, the sensor is embedded in a wall of the elongated member. In another embodiment, the sensor is positioned on an outer surface of the elongated member. 
         [0013]    The system can include in some embodiments a second sensor for sensing a parameter of the blood clot and a second indicator to indicate the sensed parameter, the second sensor connected to the second indicator. In some embodiments, the second sensor senses a density of the blood clot. In some embodiments, the second sensor is positioned on a second elongated member coaxial with the elongated member carrying the sensor for measuring pH. In some embodiments, the second sensor is proximal of the first sensor. 
         [0014]    In accordance with another aspect, the present invention provides a method for determining a pH level of blood downstream of a blood clot in a vessel of a patient comprising the steps of:
       providing an elongated flexible member;   inserting the flexible member through vasculature of the patient and past the blood clot to a position downstream of the blood clot in the vessel;   sensing a pH level of the blood downstream of the clot; and   indicating to the user the pH level of the blood to enable the user to determine a pH level of the vessel downstream of the blood clot for subsequent selection of a clot treatment approach.       
 
         [0019]    In some embodiments, the method further comprises the step of determining a density of the blood clot to determine a clot treatment method. In some embodiments, the step of determining the density of the blood clot utilizes a sensor proximal of a sensor used for sensing pH of the blood. In some embodiments, one of the density sensor and pH sensor is on a first elongated flexible member and the other sensor is on a second elongated flexible member coaxial with the first elongated member. 
         [0020]    In accordance with another aspect, the present invention provides a system for determining an oxygen level of blood in a vessel of a patient. The system comprises a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, the elongated member having a proximal portion and a distal portion and configured for insertion so the distal portion extends past a blood clot for positioning of the distal portion distal of the blood clot. A sensor is positioned at the distal portion of the elongated member for positioning distal of the blood clot. A connector connects the elongated member to an indicator, the sensor measuring the oxygen level of blood, preferably in a closed or a substantially closed system downstream of the blood clot, to thereby determine the oxygen level of the vessel downstream of the blood clot to determine the condition of the vessel to assess subsequent treatment of the blood clot. The indicator provides an indication of the oxygen level of the blood measured by the sensor. 
         [0021]    In accordance with another aspect, the present invention provides a method for determining an oxygen level of blood downstream of a blood clot in a vessel of a patient comprising the steps of:
       providing an elongated flexible member;   inserting the flexible member through vasculature of the patient and past the blood clot to a position downstream of the blood clot in the vessel;   sensing an oxygen level of the blood downstream of the clot; and   indicating to the user the oxygen level of the blood to enable the user to determine an oxygen level of the vessel downstream of the blood clot for subsequent selection of a clot treatment approach.       
 
         [0026]    In accordance with another aspect of the present invention, a system for determining a density of a blood clot in a vessel of a patient for subsequent selection of a treatment method is provided. The system comprises a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, the elongated member having a proximal portion and a distal portion and the distal portion configured for insertion adjacent the blood clot. A sensor is positioned at the distal portion of the elongated member. A connector connects the elongated member to an indicator, the sensor determining the density of the blood clot and the indicator providing an indication of the determined density. 
         [0027]    In one embodiment, the flexible elongated member comprises a catheter. In another embodiment, the flexible elongated member comprises a guidewire. 
         [0028]    The system in some embodiments further comprises a transmitter at the distal portion of the elongated member for transmitting ultrasonic waves toward the blood clot, and the density of the blood clot is determined by ultrasonic wave feedback. The system in some embodiments can further include a pH sensor for measuring pH of blood downstream of the clot and an indicator for indicating measured pH. 
         [0029]    The present invention provides in another aspect a method for determining a density of a blood clot in a vessel of a patient for subsequent selection of a clot treatment method. The method comprises: 
         [0030]    providing a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, the elongated member having a proximal portion and a distal portion, the elongated member distal portion configured for insertion adjacent a blood clot;
       transmitting ultrasonic waves toward the blood clot; and   determining the density of the blood clot based on the ultrasonic wave feedback.       
 
         [0033]    In some embodiments, the method further provides a visual indication of the determined density. 
         [0034]    In some embodiments, the method further includes positioning the elongated member so that a distal tip extends past the blood clot and a density sensor is positioned proximal of the distal tip within the blood clot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Preferred embodiments of the present disclosure are described herein with reference to the drawings wherein: 
           [0036]      FIG. 1  is a side view of a first embodiment of the system of the present invention illustrating a catheter coupled to a pH reader and showing the catheter tip positioned distal of the blood clot; 
           [0037]      FIG. 2A  is a close up perspective view of the pH reader of  FIG. 1 ; 
           [0038]      FIG. 2B  is a close up perspective view of an oxygen level reader; 
           [0039]      FIG. 3A  is a close up view of the catheter tip of  FIG. 1  showing the pH sensor on an outer surface of the catheter for determining blood pH; 
           [0040]      FIG. 3B  is a close up view of the catheter tip showing the pH sensor embedded in the wall of the catheter in accordance with an alternate embodiment; 
           [0041]      FIG. 4  is a close up perspective of the coupler of  FIG. 1  for connecting the pH reader cable to the catheter; 
           [0042]      FIG. 5  is a close up view of the vasculature illustrating the catheter tip of  FIG. 1  positioned past a blood clot; 
           [0043]      FIG. 6  is a side view of an alternate embodiment of the system of the present invention illustrating a guidewire coupled to a pH reader and showing the guidewire positioned distal of the blood clot; 
           [0044]      FIG. 7  is a close up perspective view of the coupler connecting the pH reader cable to the guidewire; 
           [0045]      FIG. 8A  is a close up view of the guidewire of  FIG. 6  positioned distal of the clot and showing the pH sensor on the outer tip of the guidewire; 
           [0046]      FIG. 8B  is a cutaway view showing the pH sensor embedded in the wall of the guidewire in accordance with an alternate embodiment; 
           [0047]      FIG. 8C  is a close up view of an alternate embodiment having a density sensor spaced from the distal tip; 
           [0048]      FIG. 9A  is side view of an alternate system of the present invention illustrating a catheter coupled to a density reader and showing the catheter tip positioned distal of the blood clot; 
           [0049]      FIG. 9B  is a close up view of the distal portion of the catheter of  FIG. 9A  showing the density sensor within the clot; 
           [0050]      FIG. 10  is a close up view of the density reader of  FIG. 9A  showing a clot density reading; 
           [0051]      FIG. 11A  is a side view of an alternate embodiment of the system of the present invention illustrating a guidewire coupled to a density reader and showing the guidewire positioned distal of the blood clot; 
           [0052]      FIG. 11B  is a close up view of the distal portion of the guidewire of  FIG. 11A , with the clot broken away to show the density sensor within the clot; 
           [0053]      FIG. 12A  is a side view of another alternate system of the present invention showing a catheter coupled to a pH reader and a guidewire coupled to a density reader, and further showing the catheter tip and guidewire positioned distal of the blood clot; 
           [0054]      FIG. 12B  is a close up view of the distal end of the catheter and guidewire of  FIG. 12A , showing retraction of the catheter to expose the density sensor on the guidewire; and 
           [0055]      FIG. 13  is an enlarged view of the density reader of  FIG. 12A . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0056]    The present invention provides a system for determining the health or condition of the vasculature distal of the blood clot. This aids the physician in assessing the effect of removal of the blood clot from the vessel. The present invention also provides a system for determining the type of blood clot. This enables the physician to assess the best mode of treatment of the blood clot. These two systems can be used independently or alternatively can be used together. That is, it is contemplated that only one of the systems is utilized so the user measures only one of the parameters, i.e., either health of vasculature or type of clot. However, it is also contemplated that both systems be utilized so the user can determine both parameters. These systems are described in detail below. 
       Vasculature Determination 
       [0057]    Turning first to the system for determining the health or condition of the vasculature, this system is illustrated in  FIGS. 1-8 , with  FIGS. 1-5  illustrating an embodiment where the pH sensor is located on a catheter and  FIGS. 6-8B  illustrating an embodiment where the pH sensor is located on a guidewire. It is also contemplated that a pH sensor can be positioned on the catheter and on the guidewire, and it is also contemplated that one or more pH sensors can be positioned on the catheter and one or more pH sensors can be positioned on the guidewire. Multiple sensors would enable different regions of the blood (and therefore the vasculature) to be measured. In certain embodiments utilizing multiple pH sensors, the sensors can be spaced apart sufficiently so that a pH measurement can be taken both upstream and downstream of the blood clot for comparative purposes in assessing vasculature health. 
         [0058]    The system for measuring pH is beneficial since in certain instances, the vitality of the vasculature distal to the clot is compromised once the clot lodges in place. Vasculature that has been deprived of oxygenated blood will necrose and become friable. Once blood flow is restored after clot removal, such blood flow could potentially cause a hemorrhagic event, which means the vessel can bleed out and burst open. Therefore, this system provides a way of determining the health of the vasculature distal to the clot so the physician could determine if clot removal is advisable or take other precautions during clot removal. That is, the physician will be able to determine if the clot should be removed based upon the pH content of the vasculature distal to the clot. 
         [0059]    Such determination can be done measuring pH. It could also be accomplished in an alternate embodiment by sensing oxygen levels in the blood which would provide an indication of the health of the vasculature. Other parameters could also be measured. 
         [0060]    With respect to pH, it is understood that intracellular pH is important in the maintenance of normal cell function. Blood pH is regulated by a system of buffers that continuously maintain its normal range of 7.35 to 7.45. Blood pH drop below 7 or above 7.45 can cause serious problems, including death. Studies have shown that carbon dioxide plays a vital role in blood pH abnormality. Carbon dioxide serves as a buffer. As carbon dioxide becomes depleted, the pH drops and acidosis and/or apoptosis occurs. 
         [0061]    With the presence of a blood clot, there is essentially a closed system (or substantially closed system) created in the vasculature since blood flow downstream of the clot has mostly stopped. Being a closed system, the pH of the blood can be measured and the blood pH will be indicative of the pH of the adjacent vasculature. Thus, the measurement of the blood pH as described herein provides an inexpensive, accurate and effective way to determine the pH and thus the health of the adjacent vasculature. The pH can be measured utilizing known techniques such as an ionic potential sensor that converts the activity of a specific ion dissolved in a solution into an electric potential which can be measured. Known glass and crystalline membranes can be utilized. 
         [0062]    It is also contemplated that instead of measuring blood pH, the oxygen level of the blood can be measured downstream of the blood clot, preferably in a closed or substantially closed system, to thereby determine the health of the vasculature. 
         [0063]    Turning more specifically to the system of  FIGS. 1-5 , catheter  10  has a proximal portion  12  and a distal portion  14 . The catheter tube  16  is sufficiently flexible to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. An RHV (rotating hemostatic valve)  20  is attached to the catheter hub  22  and includes a side arm  24  for fluid injection and/or aspiration. Coupler (connector)  30  is attached to the catheter  10 , and is connected to cable  34  which is connected to pH reader (meter)  40 . In one embodiment, as shown in  FIG. 4 , the coupler  30  is u-shaped with opening  31  between the legs of the “u” dimensioned to frictionally clamp onto the outer wall of the catheter  10 . That is, the coupler  30  is shown in the embodiment of  FIG. 1  in the form of a U-shaped clip with the radius of the U smaller than that of the outer wall of the catheter so it flexes outwardly when placed over the strain relief of the catheter and then is frictionally retained on the catheter. In another embodiment, a second connector (coupler) half is placed opposite the connector to form a 360 degree clip or clamp surrounding the outer wall of the catheter to retain the connector on the catheter  10 . Other methods of attachment are also contemplated such as magnetic attachments. Cable  34  is connected to the coupler at one end  35  and connected at the opposing end  36  to reader  40 . As shown ( FIG. 1 ), the coupler  30  is attached to the region of catheter  10  just distal of hub  22 , although other locations are also contemplated. The coupler  30  can be attached to the strain relief of the catheter  10  to enhance coupling. 
         [0064]    The pH sensor  26  for measuring blood pH is positioned at the distal portion  14  of the catheter  10  and is electrically coupled to cable  34  via a pair of wires (not shown) extending from the sensor  26  to the coupler  30  and/or cable  34 . The wires can be embedded in a wall of the catheter  10  or alternatively extend through a lumen in the catheter  10 . In the embodiment of  FIG. 3A  the sensor  26  is positioned on an outer wall of the catheter  10 , extending circumferentially around 360 degrees. The sensor can also be incorporated into a marker band at the tip of the catheter  10 . In the alternate embodiment of  FIG. 3B , the sensor  26 ′ is positioned inside the catheter  10 , either internal of the inner catheter wall or alternatively embedded in the wall of the catheter  10 ′. Wires  27  connect the sensor  26 ′ to the conductor  30  and/or cable  24 , with two lines coming into the reader  40  with two lines extending to the sensor  26 . 
         [0065]    The pH reader  40  provides an indicator device and contains an on off switch  42 . A reading  44  provides a visual indication, as a numeric value, of the measured pH of the blood to inform the user of the pH of the blood, and therefore the vasculature.  FIG. 2  shows by way of example a reading of 6.4 which is below the normal range of 7.35 to 7.45 and thus indicates acidosis has likely occurred which affects (compromises) the vasculature structure. 
         [0066]    In use, the catheter  10  (or  10 ′) can be inserted utilizing known methods, e.g., through a femoral approach or a brachial approach, and advanced through the vascular system to the desired treatment site, e.g. a cerebral artery A. The catheter tip  11  is advanced past the blood clot C (see e.g.,  FIG. 5 ). The sensor is activated to measure pH, with the pH reader turned on so that pH value can be determined. As noted above, the closed system advantageously enables the user to determine the vasculature condition by measuring the blood pH rather than the pH of the vasculature itself. Proper treatment approaches, e.g., deciding whether the clot can be safely removed or taking other precautions to protect the vessel, can then be implemented. 
         [0067]      FIGS. 6-8B  illustrate an alternate embodiment for measuring pH utilizing a sensor on a guidewire instead of the catheter as in  FIG. 1 . In this embodiment, guidewire  50  has a proximal portion  52  and a distal portion  54 . The guidewire  50  is sufficiently rigid to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. In one embodiment the guidewire is hollow and the wire runs through the lumen from the sensor to the connector, and the wire, as in other embodiments herein, is preferably insulated. In another embodiment, the guidewire is a solid core and a polymeric jacket contains the insulated wire on an outer surface of the guidewire. The guidewire is illustrated within a lumen of a catheter  70  having a RHV  74  attached to the proximal end. The RHV  74  is attached to the hub  72  of the catheter  70  and includes a side arm  75  for injection and/or aspiration. Coupler  80  is attached to the guidewire  50 , and is connected to cable  83  which is connected to pH reader  40 . The pH reader can be the same as in the embodiment of  FIG. 1 . In one embodiment, as shown in  FIG. 7 , the coupler (connector)  80  is u-shaped with opening  81  between the legs of the “u” dimensioned to frictionally clamp onto the outer wall of the guidewire  50 . A two part connector as described above could also be utilized. Other methods of attachment are also contemplated including magnetic attachments for example. Cable  83  is connected to the coupler  80  at one end  85  and connected at the opposing end  86  to reader  40 . 
         [0068]    The pH sensor  56  is positioned at a distal end of the guidewire  50  and is electrically coupled to coupler  80  and/or cable  84  via a pair of wires (not shown) extending from the sensor  56 . The wires can be embedded in a wall of the guidewire  50  or alternatively the guidewire can have a lumen or channel through which the wires extend. In the embodiment of  FIG. 8A , the sensor  56  is positioned on an outer wall of the guidewire  50 , extending circumferentially around 360 degrees. The sensor can also be incorporated into a marker band at the tip of the guidewire  50 . In an alternate embodiment, the sensor  56 ′ and wires  57  (only one is shown) of guidewire  50 ′ can be positioned inside the guidewire  50 ′, either internal of the inner wall of the guidewire as shown in  FIG. 8B , or alternatively embedded in the wall of the guidewire. The catheter  70  through which the guidewire extends can have a marker band  79 . Note in  FIG. 8A , the catheter  70  and guidewire  50  are positioned in a cerebral artery A distal of clot C. 
         [0069]    In use, the switch  42  of the pH reader  40  is activated and the sensor  56  is activated to measure the blood pH and the pH reader provides a numeric pH value of the blood.  FIG. 6  shows a pH reading of 6.4 by way of example. Note the guidewire  50  can be inserted utilizing known methods, e.g., through a femoral approach or a brachial approach, and advanced through the vascular system to the desired treatment site, e.g. the cerebral artery. In a preferred method, first an introducer is placed in the femoral artery, and a large guidewire and guide catheter is advanced to the carotid artery. The large guidewire is removed, and replaced with a microcatheter  70  and a smaller dimensioned guidewire  50  of the present invention which contains sensor  56 . The catheter tip  71  (containing maker band  79  for imaging) and guidewire tip  51  are advanced past the blood clot C (see e.g.,  FIG. 8A ). The sensor  56  measures the pH and transmits the measurement through the wires extending in guidewire  50  back to the cable  83  which in turn transmits it to the reader  40 . As noted above, the closed system advantageously enables the user to determine the vasculature condition by measuring the blood pH rather than the pH of the vasculature (or surrounding tissue) itself. Proper treatment approaches for the treating the blood clot can then be better selected. That is, the physician can determine whether removal of the clot would be too traumatic to the vessel and risk hemorrhaging. 
         [0070]    Note the sensors are shown at the distalmost tip of the catheter ( FIGS. 1-5 ) or guidewire ( FIGS. 6-8B ) but alternatively can be spaced proximal of the distalmost tip such as the sensor  56   a  of guidewire  50   a  of  FIG. 8C . 
         [0071]    The pH sensors can be used in other applications such as in cases of gangrene or tissue dying for some other reason to intravascularly assess the vasculature or health of the tissue. 
         [0072]    In an alternate embodiment, the oxygen level of the blood can be measured which is indicative of the oxygen and thus the health of the vasculature. The system would be the same as with the above described systems, except one or more oxygen sensors (rather than pH sensors) would be provided on the catheter or the guidewire and connected to an oxygen reader (meter) such as shown in  FIG. 2B . The oxygen reader provides an indicator of the oxygen level, by providing for example a numeric value, or other indicator, to indicate a range of low to high oxygen level measurements. The sensors can be positioned on the catheter or guidewire in the similar manners of the pH sensors disclosed herein. 
       Clot Determination 
       [0073]    As noted above, the present disclosure provides a system to identify a parameter such as the composition of a clot in a vessel which will enable the physician to scientifically determine the clot makeup and determine the best course of treatment from the available tool sets. This can be achieved in accordance with one embodiment using ultrasound. 
         [0074]    More specifically, in the embodiment utilizing ultrasonic waves, the density of the clot can be estimated, in vivo, by determining the time it takes for an ultrasonic sound wave to “bounce” back from the clot. The longer the signal takes to return, the less dense the clot is. That is, an ultrasound signal will return more quickly when interacting with a denser substrate. The average densities of traditional “soft” clot or normal clot and the denser fibrin clot is determined to provide predetermined parameters, and then the system of the present disclosure compares the signal generated by the ultrasonic wave to these parameters to inform the physician of the type of clot. Thus, the system utilizes a logic circuit to determine the makeup of the clot quickly, efficiently and effectively. By way of example, a soft clot can be assigned a numeral  1  and a hard clot assigned a numeral  10 , and the clot density measured to assign a value within this range so the physician would first be informed of the type of clot before taking treatment steps, such as removal of the clot. In other words, the measured average densities of both normal clot and fibrin will provide a “baseline” incorporated into the logic-circuit which will determine, in vivo during the surgical procedure, which clot type is present within the vessel. Other numeric values or indicators are also contemplated to indicate varying densities. 
         [0075]    To generate and provide a digital or analog readout of these ultrasound signals a piezoelectric signal transducer can be used. Piezoelectric materials are crystalline structures which undergo a mechanical deformation when a certain voltage is applied to the crystal. This property is used in conjunction with an applied AC voltage applied to the crystal. As the AC voltage is applied to the piezo-material it will deform and generate a sound wave. Likewise, when a mechanical load is placed on the piezoelectric crystal a small voltage is generated. This property is used to convert an ultrasonic signal into a measurable voltage. The piezoelectric crystal has a specific voltage/frequency relationship which can be used to convert between the two. 
         [0076]    Because of these unique properties, the same piezoelectric transducer which generates an ultrasonic signal can also be used to receive the reflected signal returning from a substrate. Utilizing these properties the ΔT (change in time) can be determined between the sent signal and the received signal by having predetermined the average ΔT for both normal and fibrin clots; the designed logic circuit will be able to determine which clot is present. 
         [0077]    This ultrasonic signal is sent from within the vasculature to ensure that interference from cranial tissues, muscle, bone, etc. do not affect measurements. The size and shape of the piezoelectric crystal will determine the distance at which the measurement can be best made. 
         [0078]    Turning now to the system of  FIGS. 9A-12B , a system for determining the type of clot is illustrated, with  FIG. 9  illustrating an embodiment where the density sensor (utilizing ultrasound as described above) is on a catheter and  FIG. 11  illustrating an embodiment where the density sensor (utilizing ultrasound) is on a guidewire. It is also contemplated that a density sensor can be positioned on the catheter and on the guidewire, and it is also contemplated that one or more density sensors can be positioned on the catheter and one or more density sensors positioned on the guidewire. This enables more than one region of the clot to be measured which could be beneficial in large clots. 
         [0079]    Turning more specifically to the system of  FIGS. 9A, 9B and 10 , catheter  110  has a proximal portion  112  and a distal portion  114 . The catheter tube  116  is sufficiently flexible to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. An RHV  120  is attached to the catheter hub  122  and includes a side arm  124  for fluid injection and/or aspiration. Coupler  130  is attached to the catheter  110 , and is connected to cable  134  which is connected to density reader (meter)  140 . In one embodiment, the coupler  130  can be the same as coupler  30  of the embodiment of  FIG. 1  and can be u-shaped with an opening between the legs of the “u” dimensioned to frictionally clamp onto the outer wall of the catheter  110 . That is, the coupler can be in the form of a U-shaped clip with the radius of the U smaller than that of the outer wall of the catheter so it flexes outwardly when placed over the strain relief of the catheter and then is frictionally retained on the catheter. In another embodiment, a second connector half is placed opposite the connector to form a 360 degree clip or clamp surrounding the outer wall of the catheter to retain the connector (coupler) on the catheter  110 . Other methods of attachment are also contemplated such as magnetic attachments. A cable  134  is connected to the coupler at one end  135  and connected at the opposing end  136  to density reader  140 . As shown, the coupler  130  is attached to the region of catheter  110  just distal of hub  122 , although other locations are also contemplated. 
         [0080]    The density sensor  126  is positioned at the distal portion  114  of the catheter  110 , at the distalmost tip  115  and is electrically coupled to cable  134  via a pair of wires (not shown) extending from the sensor  126  to the coupler  130  and/or cable  134 . The wires can be embedded in a wall of the catheter  110  or alternatively extend through a lumen in the catheter  110 . The sensor  126  in the illustrated embodiment is at the distalmost tip but alternatively could be spaced from the distalmost end so the catheter tip can extend past the clot during use while the sensor is positioned within the clot. The sensor can be positioned on an outer wall of the catheter  110 , extending circumferentially around 360 degrees. The sensor can also be positioned inside the catheter  110 , either internal of the inner catheter wall or alternatively embedded in the wall of the catheter. Wires (not shown) connect the sensor to the coupler  130  and/or cable  124 . 
         [0081]    The density reader  140  provides an indicator device and contains an on off switch  142 . A reading  144  provides a visual indication as a numeric value representative of a comparative density as explained above.  FIG. 10  shows a density reading of “5” by way of example, indicating a clot density midway between the outer soft clot and outer hard clot range. Connector (coupler  120 ) is wired to the reader  140  which provides a reading of the clot type based on the signal received from the sensor  126  in response to the ultrasonic signal caused by the ultrasonic waves applied to the clot. In use, the catheter  110  can be inserted utilizing known methods, e.g., through a femoral approach or a brachial approach, and advanced through the vascular system to the desired treatment site, e.g. the cerebral artery A. The catheter tip  115  is advanced past the blood clot C (see e.g.,  FIG. 9B ) so the sensor  126  is located within the blood clot. The sensor  126  is activated, using ultrasonic waves to measure density, with the density reader providing a visual density indication so the user can decide the optimal way to treat the clot. 
         [0082]      FIG. 11A  illustrates an alternate embodiment for measuring density utilizing a sensor on a guidewire instead of the catheter as in  FIG. 9A . In this embodiment, guidewire  150  has a proximal portion  152  and a distal portion  154 . The guidewire  150  is sufficiently rigid to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. In one embodiment, the guidewire is hollow and the wires run through the lumen from the sensor to the connector, and the wires are preferably insulated. In another embodiment, the guidewire is a solid core and a polymeric jacket contains the insulated wires on an outer surface of the guidewire. The guidewire is illustrated within a lumen of a catheter  170  having a RHV  174  attached to the proximal end. The RHV  174  is attached to the hub  172  of catheter  170  and includes a side arm  175  for injection and/or aspiration. Coupler  180  is attached to the guidewire  150 , and is connected to cable  183  which is connected to density reader  140 . The density reader  140  can be the same as in the embodiment of  FIG. 10 . In one embodiment, the coupler is the same as coupler  80  of  FIG. 7  and is u-shaped with an opening in the “u” dimensioned to frictionally clamp onto the wall of the guidewire  150 . A two part connector (coupler) as described above can also be utilized. Other methods of attachment are also contemplated such as magnetic attachments. Cable  183  is connected to the coupler  180  at one end  185  and connected at the opposing end  186  to meter  140 . 
         [0083]    Density sensor  156  is positioned at a distal end of the guidewire  150 , either at the distalmost tip or spaced from the distalmost tip as shown in  FIG. 11B , and is electrically coupled to coupler  180  and/or cable  184  via a pair of wires (not shown) extending from the sensor  156 . The wires can be embedded in a wall of the guidewire  150  or alternatively the guidewire can have a lumen or channel through which the wires extend. In the embodiment of  FIGS. 11A and 11B  the sensor  156  is positioned on an outer wall of the guidewire  150 , extending circumferentially around 360 degrees. The sensor can also be incorporated into a marker band at the tip of the guidewire  150 . In an alternate embodiment, the sensor can be positioned inside the guidewire  150 , either internal of the inner wall of the guidewire in the same manner as in the embodiment of  FIG. 8B , or alternatively embedded in the wall of the guidewire. The catheter  170  through which the guidewire extends can have a marker band. Note in  FIG. 11A , the guidewire  150  is positioned with the sensor in the clot C and the catheter  170  is positioned in a cerebral artery A proximal of clot C. 
         [0084]    In use, the density sensor  156  is activated to selectively measure the density of the blood clot and with switch  42  turned on, density indication is provided. Note the guidewire  150  can be inserted utilizing known methods, e.g., through a femoral approach or a brachial approach, and advanced through the vascular system to the desired treatment site, e.g. the cerebral artery. In a preferred method, first an introducer is placed in the femoral artery, and a large guidewire and guide catheter are advanced to the carotid artery. The large guidewire is removed, and replaced with a microcatheter  170  and a smaller dimensioned guidewire  150  of the present invention which contains sensor  156 . The catheter tip  171  is advanced past the blood clot C. The guidewire  150  is positioned in the clot and in some embodiments the catheter  170  is withdrawn proximally to expose the sensor  156  within the clot C to measure the density of the clot and transmit the measurement through the wires extending in guidewire  150  back to the cable  183  which in turn transmits it to the reader  140 . Proper treatment approaches for the treating the blood clot can then be better be selected. That is, the reader  140  is used to indicate density measurement so the physician can determine the optimal way to treat the clot. 
       Combination of Systems 
       [0085]    It is contemplated that the system for determining clot density (or other clot parameter) and the system for measuring the blood pH (or other blood parameter such as oxygen) can be used together. In such system, both the density sensor and pH sensor (or oxygen sensor) along with a density and pH (or oxygen) reader are provided. Such system is shown in the embodiment of  FIGS. 12A-13 . 
         [0086]    Catheter  210  has a proximal portion  212  and a distal portion  214 . The catheter tube  216  is sufficiently flexible to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. An RHV  220  is attached to the catheter hub  222  and includes a side arm  224  for fluid injection and/or aspiration. Coupler  230  is attached to the catheter  210 , and is connected to cable  234  which is connected to pH reader (meter)  241  of reader  240 . Reader  240  provides both a pH reading and a density reading. Although shown as a single reader (meter), it is also contemplated that separate meters, such as in  FIGS. 2 and 10  could be provided. In one embodiment, the coupler  230  is identical to the embodiment of  FIG. 4 , being U-shaped with an opening in the “u” dimensioned to frictionally clamp onto the outer wall of the catheter  210 . Alternatively, a second connector (coupler) half as described above can be utilized. Other methods of attachment are also contemplated. Cable  234  is connected to the coupler  230  at one end  235  and connected at the opposing end  236  to reader  241 . As shown, the coupler  230  is attached to the region of catheter  210  just distal of hub  222 , although other locations are also contemplated. 
         [0087]    The pH sensor  226 , identical to the sensor of  FIG. 1 , is positioned at the distal portion  214  of the catheter  210  and is electrically coupled to cable  234  via a pair of wires (not shown) extending from the sensor  226  to the coupler  230  and/or cable  234 . The wires can be embedded in a wall of the catheter  210  or alternatively extend through a lumen in the catheter  210 . In the embodiment of  FIG. 12A , the sensor is positioned on an outer wall of the catheter  210 , extending circumferentially around 360 degrees in an identical manner as shown in  FIG. 3A . The sensor can also be incorporated into a marker band at the tip of the catheter  210 . In the alternate embodiment, the sensor can be is positioned inside the catheter  210  (similar to sensor  26 ′ of  FIG. 3B ), either internal of the inner catheter wall or alternatively embedded in the wall of the catheter. The pH sensor can be positioned at the distalmost tip as shown or alternatively spaced proximally of the distalmost tip. Wires connect the sensor  236  to the coupler  230  and/or cable  224 . 
         [0088]    The pH reader  241  contains an on off switch  248  to selectively provide a readout of the measured pH. A reading  244  provides a visual indication, as a numeric value, of the measured pH of the blood for the user to determine the pH of the vasculature. 
         [0089]    Guidewire  250  has a proximal portion  252  and a distal portion  254 . The guidewire  250  is sufficiently rigid to navigate the small vessels while having some rigidity to enable it to be directed around the curves of the vasculature. The guidewire  250  is illustrated within a lumen of catheter  210 . Coupler  280  is attached to the guidewire  250 , and is connected to cable  283  which is connected to density reader  245  of reader  240 . In one embodiment, the coupler  280  is the same as coupler  80  of  FIG. 7  and is u-shaped with opening in the “u” dimensioned to frictionally clamp onto the wall of the guidewire  250 . Alternatively, a second connector (coupler) half as described above can be utilized. Other methods of attachment are also contemplated. Cable  283  is connected to the coupler  280  at one end  285  and connected at the opposing end  286  to reader (meter)  245 . 
         [0090]    A density sensor  256 , which is identical to sensor  156  of  FIG. 11B , is positioned at a distal portion of the guidewire  250 , spaced proximally of the distalmost tip, and is electrically coupled to coupler  280  and/or cable  283  via a pair of wires (not shown) extending from the sensor. The wires can be embedded in a wall of the guidewire  250  or alternatively the guidewire can have a lumen or channel through which the wires extend. In the embodiment of  FIG. 12A , the sensor  256  is positioned on an outer wall of the guidewire  250  in the same manner as sensor  156  of  FIG. 11B , extending circumferentially around 360 degrees. The sensor  256  can also be incorporated into a marker band at the tip of the guidewire  250 . In an alternate embodiment, the sensor can be positioned inside the guidewire  250 , either internal of the inner wall of the guidewire in the same manner as shown in  FIG. 8B , or alternatively embedded in the wall of the guidewire. The catheter  210  through which the guidewire  250  extends can have a marker band. Note in  FIG. 12A , the catheter  210  and guidewire  250  are positioned in a cerebral artery A distal of clot C. In use, the catheter  210  can be withdrawn with respect to the guidewire  250  to expose the density sensor  256  within the clot as shown in  FIG. 12B  where the density sensor  256  is proximal of the distal tip. In the embodiment wherein the density sensor  256  is at the distalmost tip, the guidewire  250  would be withdrawn further proximally until the distalmost tip (and sensor) is positioned in the clot. 
         [0091]    In the embodiment where the pH sensor is on the guidewire (as in the embodiment of  FIG. 6 ) and the density sensor is on the catheter (as in the embodiment of  FIG. 9A ), the catheter need not be withdrawn. The density sensor  256  can be positioned proximal of the pH sensor  226  during use since the density sensor is exposed on the outside of the catheter to measure the blood clot parameter and the pH sensor is exposed on the guidewire to measure the blood parameter downstream of the blood clot. In use, the density sensor is activated to measure clot density and switch  247  of the density reader  245  of reader  240  is turned on to provide a visual numeric indication of a relative density. The pH sensor is activated either simultaneously, or at a different time, so pH reader  241  provides a visual numeric indication of blood pH. 
         [0092]    It is also contemplated that in some embodiments a pH sensor (or oxygen sensor) and a density sensor can both be positioned on a single guidewire or a single catheter. 
         [0093]    Note the guidewire  250  can be inserted utilizing known methods, e.g., through a femoral approach or a brachial approach, and advanced through the vascular system to the desired treatment site, e.g., the cerebral artery. In one method, first an introducer would be placed in the femoral artery, and a large guidewire and guide catheter would be advanced to the carotid artery. The large guidewire is removed, and replaced with a microcatheter  210  which contains a pH (or oxygen) sensor (or alternatively a density sensor), and a smaller dimensioned guidewire  250  of the present invention which contains sensor  256 . The catheter tip  271  is advanced past the blood clot C. The sensor  256  of guidewire  250  is positioned in the clot so the sensor measures the density of the clot and transmits the measurement through the wires extending in guidewire  250  back to the cable  283  which in turn transmits it to the density reader  245  of reader  240 . (In the embodiment where the catheter contains the density sensor, the guidewire can contain the pH (or oxygen) sensor). The pH sensor  226  is positioned distal (downstream) of the blood clot to measure pH of the blood distal of the clot and transmit it via wires to the cable and pH reader  241 . As noted above, the closed (or substantially closed) system advantageously enables the user to determine the vasculature condition by measuring the blood pH rather than the pH of the vasculature (and surrounding tissue) itself. Proper treatment approaches for the treating the blood clot can be better selected. The density reading provides information on the blood clot itself. As noted above, an oxygen sensor can be used in the closed or substantially closed system to determine the vasculature condition. 
         [0094]    While the above description contains many specifics, those specifics should not be construed as limitations on the scope of the disclosure, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto.