Abstract:
A method for sensing the temperature profile of a hollow body organ utilizes a catheter and a hollow guidewire. The guidewire is configured as a plurality of helical loops of greater diameter than the catheter when unconstrained. 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 The catheter can be withdrawn, leaving the guidewire in place in an expanded configuration wherein the helical loops contact the inner wall of the hollow body organ. A temperature sensor is moveable within the guidewire to sense the temperature at multiple locations.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates generally to invasive medical devices and more particularly to methods using such devices for sensing the temperature of the interior wall of a hollow body organ such as a blood vessel.  
         BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    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.  
           [0004]    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.  
           [0005]    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.  
           [0006]    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.  
           [0007]    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.  
           [0008]    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  
         [0009]    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 longitudinally moveable within the guidewire. The guidewire has an expanded configuration externally of the catheter including a plurality of helical loops of greater diameter than the catheter. The guidewire also has a contracted configuration internally of the catheter and is of a lesser diameter than the catheter.  
           [0010]    According to another aspect of the invention, 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 while securing the guidewire against substantial longitudinal movement relative to the hollow body organ, resulting in the guidewire self-expanding into helical loops in contact with the hollow body organ. As the temperature probe is advanced to a region of interest, the hollow guidewire and the probe remain within the catheter. The temperature sensing is done while the hollow guidewire is deployed out of the catheter and the temperature probe is retracted within the hollow guidewire. The temperature probe is moved through the guidewire to sense the temperature of the hollow body organ at multiple locations.  
           [0011]    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  
       [0012]    In the drawings,  
         [0013]    [0013]FIG. 1 is a perspective, partially cut-away view of an arterial hollow body organ in which a preferred embodiment of the present invention is deployed;  
         [0014]    [0014]FIG. 2 is an enlarged perspective view of the embodiment of FIG. 1;  
         [0015]    [0015]FIG. 3 is an enlarged perspective view of another preferred embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is an enlarged perspective view of a further preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 5 is a block diagram of a controller useful in connection with the embodiment of FIG. 4; and  
         [0018]    [0018]FIG. 6 is a perspective view, partially is section, of yet another preferred embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIGS. 1 and 2 show an expandable device  10  for profiling the wall of a hollow body organ. Device  10  is shown deployed in a hollow body organ comprising an arterial blood vessel  12  having an endothelium  14  forming the inner wall thereof. A plaque  16  is disposed in endothelium  14 .  
         [0020]    Device  10  includes a lumened catheter  18  having a central lumen  19 , a hollow guidewire  20  comprising a tubular helix formed of metal wire  21  or the like in the shape of a coil defining a central lumen  22 , and a temperature probe  23  disposed within the lumen  22  of guidewire  20 . The temperature probe  23  comprises a flexible elongate member  24  of sufficient stiffness to permit insertion into and withdrawal from lumen  22  of guidewire  20 , following the curves thereof, without bending or kinking. A thermal sensor  25  is disposed at the distal end of the temperature probe  23 , and conventional conductors or other signal carrying structures (not shown) are provided to convey signals from the thermal sensor along the guidewire  20  and out of the proximal end of guidewire  20  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. Thermal sensor  25  can be a thermocouple or a thermistor, for example.  
         [0021]    The temperature probe can be made of metal wire, or a suitable plastic material, or a combination of both such as a metal wire coated with lubricous polymer material such as polytetrafluoroethylene (PTFE or Teflon®), polyethylene or other lubricous polymer material as known in the art. The coils of guidewire  20  may also be coated with a lubricous polymer such as PTFE to aid the insertion and withdrawal of the temperature probe within the lumen of guidewire  20 . Such a coating also helps to thermally isolate the adjacent coils from one another and make the thermal mapping more precise. In other words, it will reduce the spread of heat from a hot zone to a normothermic zone.  
         [0022]    Guidewire  20  is made of thin wire  21  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  22  therethrough. Guidewire  20  has an outer diameter somewhat less than the inner diameter of catheter  18  to permit guidewire  20  to slide freely within the lumen  19  of catheter  18 . In addition, guidewire  20 , in its relaxed configuration, is shaped as large, loosely spaced helical loops  26 . Guidewire  20  can be deformed from this relaxed configuration under force, and when the force is removed guidewire  20  returns to the relaxed, looped configuration.  
         [0023]    Temperature probe  23  has a stiffness substantially less than that of the guidewire  20  and has flexibility while having excellent pushability. Flexibility permits temperature probe  23  to follow the curves of helical loops  26  of guidewire  20  without forcing guidewire  20  to become straight.  
         [0024]    The self-looping characteristic of guidewire  20  can be accomplished in several ways. One way is to construct guidewire  20  of spring steel that can be deformed into a relatively straight configuration when withdrawn into catheter  18 , but which springs back to its looped configuration when extruded from catheter  18  and released from constraint. Another way is to construct guidewire  20  of superelastic nitinol and take advantage of the martensitic transformation properties of nitinol. Guidewire  20  can be inserted into catheter  18  in its straight form and kept cool within the catheter by the injection of cold saline through catheter  18  and over guidewire  20 . Upon release of guidewire  20  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.  
         [0025]    Guidewire  20  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  20  include copper, constantan, chromel or alumel.  
         [0026]    In use, the procedure is to first advance the catheter, separately, or together with the hollow guidewire and the temperature probe therewithin, to the region of interest. Thereafter the hollow guidewire and the temperature probe are deployed beyond the distal end of the catheter. At this time the temperature probe can be positioned to a desired longitudinal location within the guidewire, preferably so that the tip of the probe is at the distal end of the deployed guidewire. Preferably, the temperature probe is inserted into the lumen  22  of guidewire  20  from the proximal end until the tip with the thermal sensor  25  is disposed at the distal end of guidewire  20 . Guidewire  20  is inserted into the lumen  19  of catheter  18  from the proximal end, thereby constraining guidewire  20  into a substantially straight configuration. Using conventional percutaneous insertion techniques, access to the blood vessel  12  is obtained surgically and device  10  is advanced through the blood vessel  12  to the region of interest.  
         [0027]    To deploy the probe, guidewire  20  is secured against movement relative to the patient, catheter  18  is slowly withdrawn such that guidewire  20  emerges from the distal end of catheter  20  and reverts to its looped configuration within the blood vessel  12 . Guidewire  20  remains substantially fixed in the axial direction relative to the blood vessel  12  as catheter  18  is withdrawn, with the reformed loops  26  springing radially outwardly into contact with the vessel wall  14 . The relative lack of movement between guidewire  20  and vessel wall  14  alleviates the risk of damage to vessel wall  14  and the risk of rupturing unstable plaque.  
         [0028]    With guidewire  20  exposed and lying in helical contact with the wall  14  of blood vessel  12 , the temperature probe  23  is able to sense the localized temperature of the vessel wall  14  through the guidewire  20  at the region where the thermal sensor  25  is located. By slowly withdrawing the temperature probe  23  from guidewire  20 , the thermal sensor  25  traverses a helical path around the wall  14  of the blood vessel  12 , permitting temperature measurements to be taken at intervals of different regions of the vessel wall  14 . By withdrawing the temperature probe  23  at a constant rate, the location of the thermal sensor  25  relative to the distal end of the guidewire  20  can be determined as a function of time, so that a temperature profile of the blood vessel  12  can be mapped.  
         [0029]    Once the mapping is completed, the catheter  18  can be pushed forward again while securing guidewire  20  against longitudinal movement. Catheter  18  will thereby re-sheath guidewire  20  and constrain it in a substantially straight configuration for withdrawal from the blood vessel  12  so that the temperature probe will be able to advance to the forward position.  
         [0030]    [0030]FIG. 3 shows a second preferred embodiment of an expandable device  110  for profiling the wall of a hollow body organ. Device  110  can be deployed in a hollow body organ in a manner similar to that shown in FIG. 1 and described above with respect to the first embodiment of expandable device  10 . Components of device  110  that are similar in structure and function to corresponding components of device  10  of FIG. 1 are designated by like reference numerals in the  100  series but having the same last two digits. The description of device  10  above applies also to device  110  unless described otherwise below.  
         [0031]    Device  110  includes a lumened catheter  118 , a hollow guidewire  120 , and a temperature probe  123  disposed within the lumen  122  of guidewire  120 . The temperature probe  123  comprises a flexible elongate member  124  of sufficient stiffness to permit insertion into and withdrawal from lumen  122  of guidewire  120 , following the curves thereof, without bending or kinking. A thermal sensor  125  is disposed at the distal end of the temperature probe  123 , sensor  125  comprising a dog-leg bend at the distal end of elongate member  124  of sufficient length and angular orientation to remain in contact with the interior surface of lumen  122  of guidewire  120  as temperature probe  123  is moved axially within guidewire  120 .  
         [0032]    Guidewire  120  and thermal sensor  125  are composed of dissimilar metals such that contact therebetween forms a thermocouple junction that generates an electrical voltage proportional to the temperature of the thermocouple junction. Elongate member  124  of temperature probe  123  comprises one conductor and guidewire  120  comprises another conductor of the resulting thermocouple for conveying signals from the thermal sensor  125  to the proximal end of guidewire  120  for connection to appropriate signal processing apparatus that converts the signals to a temperature indication. Suitable materials for guidewire  120  and thermal sensor  125  to create a thermocouple include copper, constantan, chromel, alumel, and the like, the lead serving as the thermal sensor  125  being suitably insulated except at the tip thereof.  
         [0033]    Device  110  of FIG. 3 can be used in a manner substantially similar to the manner of use described above with respect to device  10  of FIG. 1.  
         [0034]    [0034]FIG. 4 shows yet another preferred embodiment of an expandable 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 shown in FIG. 1 and described above with respect to the first embodiment of expandable device  10 . Components of device  210  that are similar in structure and function to corresponding components of device  10  of FIG. 1 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.  
         [0035]    Device  210  includes a lumened catheter  118  and a hollow guidewire  120 . The inner surface of lumen  222  of guidewire  220  is lined with a thermochromic material  230  that is sensitive to a change of temperature of the guidewire  220 . The color of the thermochromic material  230  varies as a function of temperature.  
         [0036]    Disposed within lumen  222  of guidewire  220 , inwardly of thermochromic material  230 , is an optical probe  232  including an illuminating optical fiber  234  having a radially emitting diffuser  236  at the distal end thereof, and a sensing optical fiber  238  having a conically beveled distal end  240  for collecting light. Optical fibers  234  and  238  are moveable in unison within lumen  222  in a manner similar to that of temperature probes  23  and  123  described above with reference to FIGS.  1 - 3 . An illuminating electromagnetic radiation source is connected to the proximal end of illuminating optical fiber  234  provides illuminating radiation that is guided by optical fiber  234  to the region of interest within the hollow body organ, and diffused radially by diffuser  236  to illuminate the interior of lumen  222 , particularly thermochromic material  230 . The illuminating radiation can be in the visible, infrared or ultraviolet portions of the spectrum. Radiation from diffuser  236  is differentially absorbed and reflected by thermochromic material  230 , according to the color of material  230  which is indicative of the temperature of guidewire  220  in contact with the wall of the hollow body organ in the region of interest.  
         [0037]    The light reflected from thermochromic material  230 , having wavelengths indicative of the color thereof, is collected by distal end  240  and directed toward the proximal end of sensing optical fiber  238 . An appropriate optical reflectance spectrometry device connected to the proximal end of sensing optical fiber  238  generates an electrical signal indicative of the color, and therefore temperature, of thermochromic material  230 .  
         [0038]    [0038]FIG. 5 shows a block diagram of a control device  250  suitable for use with device  210  of FIG. 4. An optical transmitter  252  generates light for transmission through optical fiber  238  as discussed above. Transmitter  252  is operably connected to a wavelength generator  254  that generates signals indicative of the wavelength of the light transmitted by transmitter  252 , which signal is conveyed as an input to a computer  256 . An optical receiver  258  receives light reflected from thermochromic material  230  (FIG. 4) through optical fiber  234  as discussed above. Receiver  258  is operably connected to a wavelength and amplitude detector  260  that generates signals indicative of the wavelength and amplitude of the light received by receiver  258 , which signals are conveyed as an input to a computer  256 . A processed output signal from computer  256  generates a graphical display  262  of detected color, i.e., temperature, as a function of linear displacement of optical probe  232  relative to catheter  218 . A mechanical pull-back device  264  is mechanically connected to optical probe  232  and is controlled by and sends feedback signals to computer  256 , which signals contribute to the generation of the display  262 .  
         [0039]    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 FIG. 1.  
         [0040]    [0040]FIG. 6 shows still another preferred embodiment of the present invention that can incorporate any of the various temperature sensing technologies described above with respect to the first, second and third embodiments. Catheter  318  includes a first portion  370  and a second portion  372  that is telescopically received within first portion  320  and axially moveable relative thereto. Hollow guidewire  320  is fixed at the distal end thereof to second portion  372 , and is received within the lumen of first portion  370  via an aperture  374 . A movable, temperature sensing transducer as described hereinabove is situated within guidewire  320 . By extending and retracting second portion  372  relative to first portion  370 , the pitch and outer diameter of loops  326  of guidewire  320  can be adjusted for optimal contact with the inner wall of hollow body organ  312 .  
         [0041]    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.