Patent Publication Number: US-2019183458-A1

Title: Photoacoustic guide support system and photoacoustic guide support method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of a photoacoustic guide support system and a photoacoustic guide support method used for catheterization. 
     2. Description of Related Art 
     As a treatment method for reestablishing blood flow of a blood vessel occluded by thrombus, there is a method of reestablishing blood flow using a small-diameter device such as a catheter. In this method, a catheter inserted from a wrist or an inguinal region is guided into an affected area to perform an examination or treatment of an occluded area. In this examination or treatment using a catheter, first, a wire having a diameter of several tenths of millimeters called a guide wire is inserted. Next, a catheter for examination or a catheter for treatment is introduced along the guide wire. 
     However, there is a case where it is difficult for the guide wire to penetrate some of lesions in which a blood vessel is occluded. A representative example is chronic total occlusion (CTO) of a coronary artery. The chronic total occlusion is a lesion in which the coronary artery is occluded for a long period of time of three months or longer. Since the blood vessel is completely occluded, blood stream cannot be observed by coronary arteriography with X-ray, and an upstream surface of the lesion may be hardened by calcification. In order to avoid penetration of the hardened area, a method called retrograde approach is frequently used. 
     In order to compensate for a decrease in blood flow rate caused by occlusion in CTO, a blood vessel called collateral channel is formed from another coronary artery. In the retrograde approach, the guide wire passes through the collateral channel such that the guide wire is penetrated from a far side of an occluded area where calcification has not occurred. However, unlike a typical coronary artery, the collateral channel has a small diameter, and the route thereof is meandering. Therefore, the penetration of the guide wire is more difficult than in a typical coronary artery. In consideration of the above-described circumstances, the degree of difficulty of a treatment for CTO is high, and a long-hour surgery is required for the treatment. The long-hour surgery is a large burden on a patient and a doctor, and it is necessary to intermittently image the heart using X-ray projection during catheterization. Therefore, the burden on the patient also increases due to an X-ray contrast agent or radiation exposure. 
     In order to solve the problem, intravascular information is obtained using a forward-viewing catheter or a guide wire in the treatment for CTO. It is considered to support the penetration of an occluded area using this method. In the catheterization, a vascular wall of a catheter side surface is observed by photoacoustic (ultrasonic) imaging or optical coherence tomography (OCT). If information regarding the forward side of a catheter can be obtained using this method, it is expected that a guide of the CTO treatment can be obtained. 
     For example, JP-T-10-506807 discloses a forward-viewing ultrasonic imaging catheter having a configuration in which “a simple forward-viewing ultrasonic catheter includes one or more transducers and ultrasonic mirrors, in which the transducers and the ultrasonic mirrors are supported by a bearing in a sealed end of a catheter, and a driving cable transmits a relative motion to the transducers and the mirror. The mirror leads the ultrasonic waves to the front of the catheter. An optical fiber can be provided to direct a laser beam for ablation of atheroma under the simultaneous intravascular ultrasonic guidance.” (see ABSTRACT). 
     In addition, WO2015/052852 discloses a blood vessel catheter system and a penetration method of a CTO lesion having a configuration in which “provided is a catheter system in which either an optical fiber catheter or a guide wire can be inserted into one lumen. With reference to an image that the optical fiber catheter is inserted into the lumen, the catheter (or the guide wire) is inserted into a CTO lesion. Next, the guide wire is inserted into the lumen to penetrate the CTO lesion.” (refer to ABSTRACT). 
     Here, there is a technical problem in that, for example, it is necessary to provide an acoustic wave receiving element on a front surface of a catheter or a guide wire, which has a diameter of about 1 mm or less, in order to perform forward imaging using photoacoustic waves (ultrasonic waves). On the other hand, in the case of OCT or intravascular endoscopy, blood needs to be removed using transparent liquid in order to prevent image deterioration caused by light scattering of the blood during imaging. Due to this problem, a forward-viewing device has not been widely used in the current CTO treatment. 
     On the other hand, recently, photoacoustic imaging has attracted attention as anew intravascular imaging method. In the photoacoustic imaging, a biological body is imaged by measuring a photoacoustic wave generated when the biological body is irradiated with a pulsed laser beam. In the photoacoustic imaging, the contrast in the optical absorption of a biological body can be imaged unlike a method of irradiating a biological body with ultrasonic waves. In addition, the photoacoustic imaging also has a characteristic in that there is little effect of light scattering of a biological body as compared to other optical imaging methods such as OCT. For example, Bo Wang et al., “Intravascular photoacoustic imaging of lipid in atherosclerotic plaques in the presence of luminal blood”, OPTIC LETTERS, Apr. 1, 2012, Vol. 37, No. 7, p. 1244 suggests a catheter for examination in which photoacoustic imaging is adopted. 
     As described above, in order to support the penetration of an occluded area, it is necessary to obtain information regarding the forward side of a catheter or the forward side of a guide wire. Further, the diameter of a catheter or a guide wire is required to be about 1 mm or less such that a device having the above-described mechanism can be inserted into a coronary artery. Further, the removal of a blood required in OCT or the like requires time and efforts, and thus it is desirable not to perform the removal. 
     In addition, when an occluded area in front is hardened by calcification or the like, it is not preferable that a force is applied to the guide wire for the penetration of the hardened area. 
     SUMMARY OF THE INVENTION 
     The present invention has been made under the above-described circumstances, and an object thereof is to efficiently perform catheterization. 
     In order to solve the problem, according to the invention, a photoacoustic guide support system includes: a measuring laser beam generator that generates a measuring laser beam; a guide wire that includes an optical fiber for emitting the measuring laser beam to a target, and a detection portion for detecting a photoacoustic wave generated when the target is irradiated with the emitted measuring laser beam; and a signal processing portion that determines whether or not the guide wire is capable of advancing based on a detection signal obtained when the detection portion detects the photoacoustic wave, wherein when the detection signal shows a predetermined pattern, the signal processing portion determines that the guide wire is capable of advancing forward and outputs the determination result to an output portion. 
     Other solving means will be appropriately described in embodiments. 
     According to the present invention, catheterization can be efficiently performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a conceptual diagram illustrating a state where a photoacoustic guide wire used in an embodiment penetrates an occluded area; 
         FIG. 1B  is an enlarged schematic cross-sectional view illustrating a part of the photoacoustic guide wire; 
         FIG. 2  is a diagram illustrating a configuration of a photoacoustic guide support system according to a first embodiment; 
         FIG. 3  is a diagram illustrating a hardware configuration of a signal processing device used in the first embodiment; 
         FIG. 4  is a flowchart illustrating a procedure of the photoacoustic guide support system that is performed in the first embodiment; 
         FIG. 5A  is a diagram illustrating an example of a detection signal before correction; 
         FIG. 5B  is a diagram illustrating an example of a correction function. 
         FIG. 5C  is a diagram illustrating an example of a detection signal after correction; 
         FIG. 6  is a diagram illustrating a state where the photoacoustic guide wire reaches the occluded area; 
         FIG. 7A  is a diagram (first) illustrating an example of a distance change of the detection signal depending on an absorption spectrum of the occluded area; 
         FIG. 7B  is a diagram (second) illustrating an example of a distance change of the detection signal depending on an absorption spectrum of the occluded area; 
         FIG. 8A  is a diagram (first) illustrating an example of a distance change of the detection signal depending on an absorption spectrum of blood; 
         FIG. 8B  is a diagram (second) illustrating an example of a distance change of the detection signal depending on an absorption spectrum of the blood; 
         FIG. 9  is a diagram illustrating the photoacoustic guide wire in a blood vessel in which the occluded area is curved; 
         FIG. 10  is a diagram illustrating a configuration of a photoacoustic guide support system according to a second embodiment; 
         FIG. 11  is a diagram illustrating a hardware configuration of a signal processing device used in the second embodiment; 
         FIG. 12  is a diagram explaining a function of a photoacoustic guide wire used in the second embodiment; 
         FIG. 13  is a flowchart illustrating a procedure of the photoacoustic guide support system that is performed in the second embodiment; 
         FIG. 14  is a diagram (absorption spectrum of the occluded area) illustrating a detection signal obtained while the photoacoustic guide wire is rotating; 
         FIG. 15  is a diagram (absorption spectrum of the blood) illustrating a distance change of the detection signal obtained while the photoacoustic guide wire is rotating; and 
         FIG. 16  is a schematic diagram illustrating a system structure of a photoacoustic guide support system according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments for implementing the present invention (referred to as “embodiment”) will be described in detail appropriately with reference to the drawings. 
     Conceptual Diagram 
       FIG. 1A  is a conceptual diagram illustrating a state where a photoacoustic guide wire  10  used in an embodiment penetrates an occluded area C. In addition,  FIG. 1B  is an enlarged schematic cross-sectional view illustrating a part of the photoacoustic guide wire  10 . 
     Here, the photoacoustic guide wire  10  is used in a catheter, but the catheter is not illustrated in the drawings other than  FIG. 16 . 
     As illustrated in  FIG. 1B , in the photoacoustic guide wire  10  according to the embodiment, an optical fiber  3  is provided in a wire portion (guide wire)  1 . Further, the photoacoustic guide wire  10  is characterized in that a photoacoustic wave detection element (detection portion)  2  that detects a photoacoustic wave W is provided. 
     As illustrated in  FIG. 1A , the photoacoustic guide wire  10  is inserted into a blood vessel V and advances through blood B that is filled in the blood vessel V. 
     In the embodiment, as illustrated in  FIG. 1A , a pulsed laser beam for measurement (measuring laser beam R 1 ) is emitted from a tip of the optical fiber  3  to the front of the photoacoustic guide wire  10 . A photoacoustic wave W generated when a biological body is irradiated with the measuring laser beam R 1  is detected by the photoacoustic wave detection element  2 . A state of a forward tissue is determined based on signal intensity and a waveform of a detection signal generated from the photoacoustic wave detection element  2  when the photoacoustic wave W is detected by the photoacoustic wave detection element  2 . 
     When it is determined that the photoacoustic guide wire  10  can advance based on the result of the determination on the state of the tissue, a doctor advances the photoacoustic guide wire  10 . However, when the forward occluded area C is hardened by calcification or the like, it may be difficult to advance the photoacoustic guide wire  10 . In this case, a laser beam for crushing a forward tissue (crushing laser beam R 2 ) is emitted from the optical fiber  3 . As a result, the occluded area C such as thrombus is crushed such that the advancement of the photoacoustic guide wire  10  is assisted. 
     Hereinafter, a specific configuration or a specific operation of the photoacoustic guide wire  10  illustrated in  FIGS. 1A and 1B  will be described. 
     First Embodiment 
     System 
       FIG. 2  is a diagram illustrating a configuration of a photoacoustic guide support system Z according to a first embodiment. In  FIG. 2 , the same components as those of  FIG. 1  are denoted by the same reference numerals, and the description thereof will not be repeated. In order not to make the drawings complicated, the occluded area C is not illustrated in  FIG. 2 . In addition, in  FIG. 2 , for easy understanding of the drawing, the size of the photoacoustic guide wire  10  with respect to the blood vessel V is illustrated to be larger than the actual size. The same shall be applied to other drawings. 
     In the photoacoustic guide support system Z, the photoacoustic guide wire  10  includes the optical fiber  3  provided in the wire portion  1  that is the same as a guide wire used for catheterization and the photoacoustic wave detection element  2 . As illustrated in  FIG. 2 , the photoacoustic wave detection element  2  is provided on a side surface of the wire portion  1 . The optical fiber  3  is connected to a measuring laser beam generator  11  that is connected to a base of the wire portion  1 . The measuring laser beam R 1  that is incident from the measuring laser beam generator  11  to the optical fiber  3  is emitted from the tip portion of the optical fiber  3 . The photoacoustic wave W, which is an ultrasonic wave generated when a biological body is irradiated with the measuring laser beam R 1 , is detected by the photoacoustic wave detection element  2 . The photoacoustic wave detection element  2  converts an intensity of the photoacoustic wave W into an electric signal (detection signal) and transmits this detection signal to a signal processing device (signal processing portion)  100 . The signal processing device  100  determines an advancing direction, that is, whether or not the occluded area C can be crushed by the laser beam, based on the transmitted detection signal. The determination on the advancing direction will be described below. The result (OK/NG) of the determination of the signal processing device  100  on the advancing direction is displayed on a display device (output portion)  160 . When a crushing laser beam emission button  171  is pressed toward the determined advancing direction, an instruction signal is transmitted to a crushing laser beam generator  12 . The crushing laser beam R 2  generated by the crushing laser beam generator  12  is emitted from the tip portion of the optical fiber  3 . The power of the crushing laser beam R 2  is stronger than that of the measuring laser beam R 1 . The emitted crushing laser beam R 2  crushes a tissue in the vicinity of the tip portion of the photoacoustic guide wire  10 . 
     Signal Processing Device  100   
       FIG. 3  is a diagram illustrating a hardware configuration of the signal processing device  100  used in the first embodiment. The description will be made appropriately with reference to  FIG. 2 . 
     The signal processing device  100  includes a memory  110 , a central processing unit (CPU)  120 , and a storage device  130  such as a hard disk (HD). Further, the signal processing device  100  includes an input device  140 , a communication device  150 , and the display device  160 . 
     On the memory  110 , a program stored in the storage device  130  is loaded. The loaded program is executed by the CPU  120 . As a result, a processing portion  111 , and a measuring laser beam controller  112 , a correction processing portion  113 , a signal processing portion  114  and a crushing laser beam controller  115  that constitute the processing portion  111  are implemented. 
     The measuring laser beam controller  112  causes the measuring laser beam generator  11  to generate the measuring laser beam R 1 . 
     The correction processing portion  113  corrects a signal intensity using a method described below. 
     The signal processing portion  114  determines a direction in which the photoacoustic guide wire  10  is to advance using a method described below. 
     When the crushing laser beam emission button  171  (refer to  FIG. 2 ) is pressed, the crushing laser beam controller  115  causes the crushing laser beam generator  12  to generate the crushing laser beam R 2 . 
     The input device  140  includes the crushing laser beam emission button  171  illustrated in  FIG. 2 . 
     The communication device  150  receives the detection signal from the photoacoustic wave detection element  2 . In addition, the communication device  150  transmits an instruction signal to the measuring laser beam generator  11  to generate the measuring laser beam R 1 , or transmits an instruction signal to the crushing laser beam generator  12  to generate the crushing laser beam R 2 . 
     The display device  160  has been described above with reference to  FIG. 2 , and thus the description thereof will not be repeated here. 
     Procedure 
       FIG. 4  is a flowchart illustrating a procedure of the photoacoustic guide support system Z that is performed in the first embodiment. 
     First, the process of  FIG. 4  starts after the tip portion of the photoacoustic guide wire  10  is inserted by the doctor up to a position where the tip portion of the photoacoustic guide wire  10  cannot advance easily. It is not necessary to strictly determine whether or not the position of the tip portion of the photoacoustic guide wire  10  is the position where the tip portion of the photoacoustic guide wire  10  cannot advance easily. For example, when the doctor determines that the tip portion of the photoacoustic guide wire  10  reaches a coronary artery, the process of  FIG. 4  may be performed. 
     After the start of the operation, the measuring laser beam controller  112  causes the measuring laser beam generator  11  to generate the measuring laser beam R 1 . As a result, the measuring laser beam R 1  is emitted from the tip of the optical fiber  3  (S 101 ). 
     When a target is irradiated with the measuring laser beam R 1 , the photoacoustic wave W is generated from the target. 
     Next, the detection signal of the photoacoustic wave W is detected by the photoacoustic wave detection element  2  (S 102 ). 
     Next, the correction processing portion  113  corrects an influence of light diffusion and absorption (intensity correction) (S 103 ). The process of Step S 103  will be described below. 
     Next, the signal processing portion  114  determines whether or not a specific peak value in the detection signal is a threshold or higher (predetermined pattern) (S 104 ). The determination depending on whether the specific peak value is the threshold or higher will be described below. 
     When the specific peak value in the detection signal is lower than the threshold as a result of Step S 104  (S 104 →No), the signal processing portion  114  displays an advancing direction change request screen on the display device  160  (S 111 ). On the advancing direction change request screen, information indicating that it is necessary to change the advancing direction is displayed. Next, the processing portion  111  returns to the process of Step S 101 . 
     When the specific peak value in the detection signal is the threshold or higher as a result of Step S 104  (S 104 → 4  Yes), the signal processing portion  114  displays a crushing laser beam irradiation screen on the display device  160  (S 112 ). The crushing laser beam irradiation screen displays information indicating that the crushing laser beam R 2  can be irradiated in a direction where the photoacoustic guide wire  10  is currently facing. 
     Next, the crushing laser beam controller  115  determines whether or not the crushing laser beam emission button  171  (emission button) is pressed by the doctor (S 121 ). 
     When the crushing laser beam emission button  171  is not pressed by the doctor (S 121 →No) as a result of Step S 121 , the processing portion  111  returns to the process of Step S 101 . 
     When the crushing laser beam emission button  171  is pressed by the doctor as a result of Step S 121  (S 121 →Yes), the crushing laser beam controller  115  causes the crushing laser beam generator  12  to generate the crushing laser beam R 2 . As a result, the crushing laser beam R 2  is emitted from the tip of the optical fiber  3  (S 122 ). 
     Next, the measuring laser beam controller  112  causes the measuring laser beam R 1  to be emitted from the tip of the optical fiber  3 . After the processing portion  111  performs the same processes as those of Steps S 102  and S 103 , the signal processing portion  114  determines whether or not the occluded area C is penetrated based on the detection signal (S 123 ). 
     When the occluded area C is not penetrated as a result of Step S 123  (S 123 →No), the processing portion  111  returns to the process of Step S 101 . 
     When the occluded area C is penetrated as a result of Step S 123  (S 123 →Yes), the processing portion  111  ends the process. 
     When the tip portion of the photoacoustic guide wire  10  is inserted again by the doctor up to the position where the tip portion of the photoacoustic guide wire  10  cannot advance easily, the photoacoustic guide support system Z performs the processes from Step S 101  again. 
     Intensity Correction Process: S 103  of FIG.  4   
     When the photoacoustic wave W is detected by the photoacoustic wave detection element  2 , a time-series detection signal is generated. The elapsed time from when the measuring laser beam R 1  is emitted corresponds to the distance from the tip portion of the photoacoustic guide wire  10 . The distance L from the tip portion of the photoacoustic guide wire  10  to the target that is irradiated with the measuring laser beam R 1  is represented by the following Expression (1). 
         L =(Δ t×v−L   0 )/2  (1)
 
     Here, Δt represents the elapsed time from when the measuring laser beam R 1  is emitted from the tip of the optical fiber  3 . In addition, v represents a sound velocity in the body, and L 0  represents the distance from the tip of the photoacoustic guide wire  10  to the photoacoustic wave detection element  2 . After the emission from the optical fiber  3 , the measuring laser beam R 1  is diffused and absorbed such that the signal intensity thereof decreases. Therefore, it is necessary to correct the detection signal using a correction function with respect to Δt, that is, the distance from the tip of the optical fiber  3 . 
     That is, as illustrated in  FIG. 5B , the correction processing portion  113  corrects the detection signal according to a correction curve of the detection signal with respect to the distance from the tip of the optical fiber  3 . 
       FIGS. 5A to 5C  are diagrams illustrating examples of the intensity correction performed in Step S 103  of  FIG. 4 . 
     Here,  FIG. 5A  illustrates an example of the detection signal before correction,  FIG. 5B  illustrates an example of the correction function, and  FIG. 5C  illustrate an example of the detection signal after correction. 
     In  FIGS. 5A to 5C , the horizontal axis represents the distance from the tip of the optical fiber  3 . That is, the origin of the horizontal axis represents the tip of the optical fiber  3 . In addition, the vertical axis represents the signal intensity. In  FIGS. 5A and 5C , the symbol T represents the detection signal transmitted from the near side of the occluded area C. 
     As illustrated in  FIG. 5A , the signal intensity of the obtained detection signal becomes weak as the distance increases. 
     Therefore, the correction processing portion  113  amplifies the signal intensity of the signal obtained from a long distance using the correction curve illustrated in  FIG. 5B . AS illustrated in  FIG. 5B , the correction curve is set such that the signal intensity is amplified as the distance increases. 
     When the intensity correction using the correction function is performed on the detection signal illustrated  FIG. 5A , even the signal obtained from a long distance is restored to the detection signal having the original signal intensity as illustrated in  FIG. 5C . 
     Determination on Advancing Direction: S 104  of FIG.  4   
     A method of performing the determination on whether or not the photoacoustic guide wire  10  can advance and the determination on the advancing direction will be described with reference to  FIGS. 6, 7A and 7B . This process corresponds to Step S 104  of  FIG. 4 . In  FIG. 6 , the same components as those of  FIG. 1  are denoted by the same reference numerals, and the description thereof will not be repeated. In addition, the horizontal axis and the vertical axis in  FIGS. 7A and 7B  are the same as those in  FIGS. 5A and 5C . Further, the detection signals illustrated in  FIGS. 7A and 7B  have undergone the intensity correction. 
     First, it is assumed that the process of the determination on the advancing direction according to the embodiment is performed only when it is difficult to advance the photoacoustic guide wire  10  due to a hardened area of the occluded area C in the blood vessel V. That is, as illustrated in  FIG. 6 , when the photoacoustic guide wire  10  reaches the occluded area C and is not likely to further advance, first, the measuring laser beam R 1  is emitted. In  FIG. 6 , a white arrow indicates an emission direction of the measuring laser beam R 1 . In photoacoustic imaging, it is known that, when a tissue is irradiated with light (laser beam) having a given wavelength, the photoacoustic wave W corresponding to the intensity of absorbed light is generated from a specific tissue that absorbs the light (laser beam) having the wavelength. For example, it is known that the blood B strongly absorbs light having a wavelength of about 600 nm or shorter, and fat strongly absorbs light having a wavelength of about 1200 nm or 1700 nm. 
       FIGS. 7A and 7B  are diagrams illustrating examples of a distance change of the detection signal when the wavelength of the measuring laser beam R 1  is matched to an absorption spectrum of a tissue of the occluded area C. Incidentally, when the wavelength of the measuring laser beam R 1  is matched to the absorption spectrum of the tissue of the occluded area C, the measuring laser beam R 1  is absorbed by the surface of the occluded area C. Therefore, the measuring laser beam R 1  does not penetrate the inside of the occluded area C. 
     In the photoacoustic guide wire  10  according to the embodiment, it is desirable that the wavelength of the measuring laser beam R 1  matches with a characteristic absorption wavelength in the tissue of the occluded area C. In this case, when the occluded area C is positioned in front of the photoacoustic guide wire  10 , the photoacoustic wave W having a strong peak as illustrated in  FIG. 7A  is generated. That is, the peak of the detection signal in  FIG. 7A  is derived from the photoacoustic wave W emitted from the occluded area C. 
     In addition, when vascular wall (or the blood B) is positioned in front of the photoacoustic guide wire  10 , the photoacoustic wave W having a weak peak as illustrated in  FIG. 7B  is generated. 
     That is, when the peak value of the detection signal after the intensity correction in Step S 103  of  FIG. 4  is higher than the predetermined threshold, the signal processing portion  114  may determine that the occluded area C is positioned in front of the photoacoustic guide wire  10 . When the occluded area C is positioned in front of the photoacoustic guide wire  10 , the emission of the crushing laser beam R 2  is performed. More specifically, when the peak value of the detection signal present at a predetermined distance or longer from the tip of the optical fiber  3  is higher than the predetermined threshold, the signal processing portion  114  determines that the direction in which the photoacoustic guide wire  10  faces is the advancing direction. 
     In this case, for example, the doctor rotates the photoacoustic guide wire  10  in various ways such that the signal processing portion  114  determines a direction in which the peak value illustrated in  FIG. 7A  is the highest as the direction in which the photoacoustic guide wire  10  is to advance. 
     A case where the detection signal after the intensity correction is higher than the predetermined threshold as illustrated in  FIG. 7A  corresponds to the case where the specific peak value is the threshold or higher in Step S 104  of  FIG. 4 . 
     As such, by using the measuring laser beam R 1  having a wavelength in the absorption spectrum of the tissue of occluded area C, a direction in which the occluded area C is present, that is, the advancing direction of the photoacoustic guide wire  10  is determined. 
       FIGS. 8A and 8B  are diagrams illustrating examples of a distance change of the detection signal when the wavelength of the measuring laser beam R 1  is matched to an absorption spectrum of the blood B. The horizontal axis and the vertical axis in  FIGS. 8A and 8B  are the same as those in  FIGS. 5A and 5C . Further, the detection signals illustrated in  FIGS. 8A and 8B  have undergone the intensity correction. 
     As illustrated in  FIGS. 8A and 8B , the wavelength of the measuring laser beam R 1  may be matched to the absorption spectrum of a biological body, in particular, the blood B having strong light absorption. 
     In this case, the detection signal derived from the blood B remaining in the occluded area C or the blood B positioned behind the occluded area C can be obtained. Even in this case, when the detection signal is a predetermined value or higher, crushing is performed. 
     Here,  FIG. 8A  is a diagram illustrating a distance change of the detection signal when the occluded area C is present in front of the photoacoustic guide wire  10  and the blood B is further present in front of the occluded area C. That is,  FIG. 8A  is a diagram illustrating a distance change of the detection signal obtained from the state illustrated in  FIG. 6 . 
     In  FIG. 8A , a peak P 11  is a reaction that is derived from the blood B present on the near side of the occluded area C, and a peak P 12  is a reaction that is derived from the blood B on the far side of the occluded area C. In the embodiment, the near side refers to the near side when seen from the photoacoustic guide wire  10 , and the far side refers to the far side when seen from the photoacoustic guide wire  10 . 
     On the other hand,  FIG. 8B  is a diagram illustrating a distance change of the detection signal when the vascular wall is present on the far side of the occluded area C. 
     That is,  FIG. 8B  is a diagram illustrating a distance change of the detection signal when the blood vessel of the occluded area C is curved (refer to  FIG. 9 ). In  FIG. 9 , the same components as those of  FIGS. 1 and 2  are denoted by the same reference numerals, and the description thereof will not be repeated. In addition, in  FIG. 9 , a white arrow indicates an emission direction of the measuring laser beam R 1 . In  FIGS. 8A and 8B , the symbol T represents the detection signal transmitted from the near side of the occluded area C. 
     In  FIG. 8B , as in the case of  FIG. 8A , a peak P 11  is a reaction that is derived from the blood B present on the near side of the occluded area C. However, in this case, as illustrated in  FIG. 9 , the blood B is not present on the far side of the occluded area C in the emission direction of the measuring laser beam R 1 . Therefore, a peak corresponding to the peak P 12  of  FIG. 8A  is not present. 
     In this case, the signal processing portion  114  determines a direction in which the pattern illustrated in  FIG. 8A  is obtained as the advancing direction of the photoacoustic guide wire  10 . Further, the signal processing portion  114  determines a direction in which the peak P 12  of  FIG. 8A  is the highest (the threshold or higher) as the advancing direction of the photoacoustic guide wire  10 . 
     That is, the specific peak value in Step S 104  of  FIG. 4  refers to the value of the peak P 12 . 
     When the photoacoustic guide wire  10  does not still penetrate the inside of the occluded area C, it is necessary to distinguish the detection signal of the blood B present on the near side of the occluded area C (refer to  FIG. 6 ). Basically, the embodiment is the case using the photoacoustic guide wire  10  when the photoacoustic guide wire  10  reaches a portion immediately before the occluded area C as illustrated in  FIG. 6 . Therefore, it is conceivable that the thickness of a layer of the blood B on the near side of the occluded area C is limited. Accordingly, the detection signal corresponding to a predetermined distance, for example, 1 mm from the tip portion of the photoacoustic guide wire  10  may be ignored. As a result, the risk of making an erroneous determination based on the detection signal obtained from the blood B on the near side of the occluded area C can be avoided. That is, by ignoring the peak  11  in  FIG. 8A or 8B , the signal processing portion  114  can determine the advancing direction only based on the peak  12 . 
     The measuring laser beam R 1  having the absorption spectrum of the blood B may be used when whether or not the occluded area C is present near the photoacoustic guide wire  10  is not clear. As such, by using the measuring laser beam R 1  having the absorption spectrum of the blood B, a guide of the advancing direction can be obtained even when whether or not the occluded area C is present near the photoacoustic guide wire  10  is not clear. In addition, by using the measuring laser beam R 1  having the absorption spectrum of a biological body, in particular, the blood B having strong light absorption, the advancing direction can be determined with high accuracy. 
     The measuring laser beam R 1  having the absorption spectrum of the blood B and the measuring laser beam R 1  having the absorption spectrum of the tissue of the occluded area C can be selectively used according to the circumstances. 
     It is known that, regarding the photoacoustic wave W generated by the irradiation of the measuring laser beam R 1 , the signal intensity and the waveform vary depending on optical characteristics of the tissue of the irradiated portion. By recognizing the forward state of the photoacoustic guide wire  10  based on the information of the photoacoustic wave W, the advancement of the photoacoustic guide wire  10  in a direction that is not the advancing direction can be avoided. In addition, even when the photoacoustic guide wire  10  enters a false lumen, a guide for returning the photoacoustic guide wire  10  to the inside of the original blood vessel V (true lumen) can be obtained. Further, when a calcified portion is present in front of the photoacoustic guide wire  10 , the calcified portion is crushed by the crushing laser beam R 2  such that the photoacoustic guide wire  10  can easily advance. 
     In a hole that is formed in the occluded area C by the photoacoustic guide wire  10  according to the embodiment, for example, a balloon or a stent is provided. That is, by emitting the crushing laser beam R 2  in a direction that is determined as the advancing direction, the hole for providing a balloon or a stent can be obtained. 
     In addition, since the photoacoustic wave detection element  2  is provided on the wire portion  1 , the advancing direction can be determined based on the detection signal obtained by the photoacoustic guide wire  10  itself. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 10 to 15 . 
     In the first embodiment, whether or not the photoacoustic guide wire  10  can advance forward is determined. On the other hand, in the second embodiment, the advancing direction is indicated. 
     Photoacoustic Guide Support System Za 
       FIG. 10  is a diagram illustrating a configuration of a photoacoustic guide support system Za according to the second embodiment. 
     Differences between the signal processing device  100  illustrated in  FIG. 2  according to the first embodiment and the photoacoustic guide support system Za illustrated in  FIG. 10  are as follows. 
     (1) A photoacoustic guide wire  10   a  includes a refraction portion  4  that is configured such that a laser beam R is emitted in an oblique direction with respect to a central axis of an optical fiber  3   a.  Here, the laser beam R includes the measuring laser beam R 1  and the crushing laser beam R 2 . The refraction portion  4  may have a configuration in which a tip of the optical fiber  3   a  (and a wire portion  1   a ) is cut obliquely as illustrated in  FIG. 10 , or may have a configuration in which the tip portion of the optical fiber  3  (refer to  FIG. 2 ) is curved. Alternatively, as the refraction portion  4 , a lens or the like may be used. Here, the tip of the optical fiber  3   a  (and the wire portion  1   a ) may be configured to be cut obliquely. 
     (2) A rotation control device (rotation controller, rotation angle detection portion)  20  that controls rotation of the photoacoustic guide wire  10   a  and measures a rotation angle of the photoacoustic guide wire  10   a  is provided in the photoacoustic guide wire  10   a.    
     (3) A signal processing device  100   a  controls the rotation of the photoacoustic guide wire  10   a.    
     Since the other configurations are the same as those of the photoacoustic guide support system Z illustrated in  FIG. 2 , the same components as those in  FIG. 2  are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Signal Processing Device  100   a    
       FIG. 11  is a diagram illustrating a hardware configuration of the signal processing device  100   a  used in the second embodiment. In  FIG. 11 , the same components as those of  FIG. 3  are denoted by the same reference numerals, and the description thereof will not be repeated. The description will be made appropriately with reference to  FIG. 10 . 
     A difference of the signal processing device  100   a  from the signal processing device  100  illustrated in  FIG. 3  is that a processing portion  111   a  includes a rotation processing portion (rotation controller)  116 . 
     The rotation processing portion  116  causes the rotation control device  20  to rotate the photoacoustic guide wire  10   a  and obtains the rotation angle of the photoacoustic guide wire  10   a  transmitted from the rotation control device  20 . 
       FIG. 12  is a diagram explaining a function of the photoacoustic guide wire  10   a  used in the second embodiment. In  FIG. 12 , the same components as those of  FIG. 10  are denoted by the same reference numerals, and the description thereof will not be repeated. 
     In the second embodiment, as in the first embodiment, it is assumed that the photoacoustic guide wire  10   a  advances up to a position where the photoacoustic guide wire  10   a  cannot advance easily. 
     Here, an appropriate advancing direction is determined by rotating the photoacoustic guide wire  10   a.  It is desirable that the photoacoustic guide wire  10   a  is automatically rotated by the rotation control device  20 . However, the photoacoustic guide wire  10   a  may be manually rotated. During the rotation of the photoacoustic guide wire  10   a,  the measuring laser beam R 1  is emitted from the tip of the optical fiber  3   a  (indicated by a white arrow in  FIG. 12 ). The emitted measuring laser beam R 1  is emitted by the refraction portion  4  in an oblique direction with respect to the central axis of the optical fiber  3   a.  As a result, the measuring laser beam R 1  is also emitted while being rotated. 
     Detection signals are detected from respective rotation angles. The detected detection signals are associated with each other by the signal processing device  100   a.  This configuration will be described below. 
     It is assumed that the blood vessel V, the occluded area C, the blood B, and the photoacoustic guide wire  10   a  have a positional relationship illustrated in  FIG. 12 . In addition, the wavelength of the emitted measuring laser beam R 1  has a characteristic absorption wavelength with respect to the occluded area C as in the case of the first embodiment. In the case of the positional relationship illustrated in  FIG. 12 , a direction in which the photoacoustic guide wire  10   a  is to advance is a lower right direction. Here, in order to determine the direction in which the photoacoustic guide wire  10   a  is to advance, first, the photoacoustic wave detection element  2  detects the photoacoustic wave W while the photoacoustic guide wire  10   a  is rotating. 
     Procedure 
       FIG. 13  is a flowchart illustrating a procedure of the photoacoustic guide support system. Za that is performed in the second embodiment. In  FIG. 13 , the same processes as those of  FIG. 4  are denoted by the same step numbers, and the description thereof will not be repeated. The description will be made appropriately with reference to  FIG. 11 . 
     In Step S 103 , after the intensity correction, the rotation processing portion  116  rotates the photoacoustic guide wire  10   a  at a predetermined angle (S 201 ). The processes of Steps S 101  to S 103  are processes of obtaining the detection signal corresponding to one rotation angle. 
     The rotation processing portion  116  determines whether or not the rotation ends (S 202 ). That is, the rotation processing portion  116  determines whether or not the photoacoustic guide wire  10   a  is rotated by 360 degrees based on the rotation angle obtained from the rotation control device  20 . 
     When the rotation does not end as a result of Step S 202  (S 202 →No), the processing portion  111   a  returns to the process of Step S 101 . 
     When the rotation ends as a result of Step S 202  (S 202 →Yes), the rotation processing portion  116  determines the rotation angle (S 203 ). A method of determining the rotation angle will be described below. At this time, the determined rotation angle may be displayed on the display device  160 . 
     The rotation processing portion  116  rotates the photoacoustic guide wire  10   a  to the rotation angle determined in Step S 203  (S 204 ). 
     Next, the crushing laser beam controller  115  determines whether or not the crushing laser beam emission button  171  (emission button) is pressed by the doctor (S 121   a ). 
     When the crushing laser beam emission button  171  is not pressed by the doctor as a result of Step S 121   a  (S 121   a →No), the processing portion  111   a  returns to the process of Step S 121   a.    
     When the crushing laser beam emission button  171  is pressed by the doctor as a result of Step S 121   a  (S 121   a →Yes), the crushing laser beam controller  115  causes the crushing laser beam R 2  to be emitted (S 122 ). Then, the processing portion  111   a  performs the process of Step S 123 . 
     Determination on Rotation Angle: S 203  of FIG.  13   
     Here, the process (S 203 ) of determining the rotation angle in  FIG. 13  will be described with reference to  FIGS. 14 and 15 . 
       FIG. 14  is a diagram illustrating the detection signal obtained while the photoacoustic guide wire  10   a  is rotating in the example illustrated in  FIG. 12 .  FIG. 14  illustrates an example in which the absorption spectrum of the measuring laser beam R 1  is matched to the absorption spectrum of the tissue of the occluded area C. Therefore, in each of detection signals obtained in respective angles in the example of  FIG. 14 , only one peak appears. 
     In  FIG. 14 , the horizontal axis represents the distance from the tip of the optical fiber  3 , and the vertical axis represents the rotation angle θ. In addition, the symbol T represents the detection signal transmitted from the near side of the occluded area C. 
     The detection signal becomes weak as the measuring laser beam faces in a direction of the vascular wall, and the detection signal becomes strong as the measuring laser beam faces in a direction of the occluded area C. Accordingly, a direction in which the peak of the detection signal is the highest is the advancing direction. In the example of  FIG. 14 , the peak of a detection signal  301  is the highest (predetermined pattern). Therefore, a direction of the rotation angle θ at which the detection signal  301  is obtained is the advancing direction. 
     As such, by using the measuring laser beam R 1  having a wavelength in the absorption spectrum of the tissue of occluded area C, a direction in which the occluded area C is present, that is, the advancing direction of the photoacoustic guide wire  10  is determined. 
       FIG. 15  is a diagram illustrating a distance change of the detection signal obtained while the photoacoustic guide wire  10   a  is rotating in the example of  FIG. 12 . Here, the symbol T represents the detection signal transmitted from the near side of the occluded area C. 
       FIG. 15  illustrates an example in which the absorption spectrum of the measuring laser beam R 1  is matched to the absorption spectrum of the tissue of the blood B. Therefore, in each of detection signals obtained in individual angles in the example of  FIG. 14 , two peaks P 21  and P 22  appear. That is, the peak P 21  is derived from the blood B present on the near side of the occluded area C, and the peak P 22  is derived from the blood B present on the far side of the occluded area C (refer to  FIG. 8A ). 
     In  FIG. 15 , as in the case of  FIG. 14 , the horizontal axis represents the distance from the tip of the optical fiber  3 , and the vertical axis represents the rotation angle θ. 
     Referring to  FIG. 12 , the peak  22  in  FIG. 15  is low when the measuring laser beam R 1  faces a direction opposite to a direction in which blood vessel V is curved. In addition, referring to  FIG. 12 , the peak P 22  in  FIG. 15  is high when the measuring laser beam R 1  faces a lower right direction. Accordingly, a direction in which the peak P 22  is the highest (predetermined pattern) is the advancing direction. In the example of  FIG. 15 , the peak P 22  of a detection signal  302  is the highest. Therefore, a direction of the rotation angle θ at which the detection signal  302  is obtained is the advancing direction. 
     As such, by using the measuring laser beam R 1  having the absorption spectrum of the blood B, a guide of the advancing direction can be obtained even when whether or not the occluded area C is present near the photoacoustic guide wire  10  is not clear. In addition, by using the measuring laser beam R 1  having the absorption spectrum of a biological body, in particular, the blood B having strong light absorption, the advancing direction can be determined with high accuracy. 
     When the advancing direction is determined, the rotation processing portion  116  operates the photoacoustic guide wire  10   a  to face the advancing direction. Next, the crushing laser beam R 2  is emitted. 
     When the peaks of the detection signals obtained at individual rotation angles are the same, the signal processing portion  114  determines that the photoacoustic guide wire  10   a  can advance forward. 
     According to the second embodiment, the advancing direction of the photoacoustic guide wire  10   a  can be determined more easily than in the first embodiment. 
     Third Embodiment 
     Next, the third embodiment of the present invention will be described with reference to  FIG. 16 . 
     In the third embodiment, unlike the first and second embodiments, the photoacoustic wave detection element  2  is not provided in the photoacoustic guide wire  10  (refer to  FIG. 2 ). 
     System 
       FIG. 16  is a schematic diagram illustrating a system structure of a photoacoustic guide support system Zb according to the third embodiment. In order not to make the drawings complicated, the occluded area is not illustrated in  FIG. 16 . 
     In the photoacoustic guide support system Zb illustrated in  FIG. 16 , unlike the first and second embodiments, a separate catheter  30  from the photoacoustic guide wire  10   b  is provided. 
     The catheter  30  has a tubular configuration, in which the photoacoustic guide wire  10   b  is movable (capable of advancing and retreating in an axial direction of the catheter  30 ). 
     In addition, in the example of  FIG. 16 , a photoacoustic wave detection element  2   b  is provided in a ring shape at the tip of the catheter  30 . 
     An operation of the photoacoustic guide support system Zb according to the third embodiment is the same as the photoacoustic guide wire  10   b  according to the first embodiment, and thus the description thereof will not be repeated. 
     In addition, the photoacoustic guide wire  10   b  according to the third embodiment may have a configuration in which the measuring laser beam R 1  and the crushing laser beam R 2  are emitted in an oblique direction with respect to the central axis of the photoacoustic guide wire  10   b  and the rotation control device  20  is provided. That is, the photoacoustic guide support system Zb according to the third embodiment may have the same configuration as that of the second embodiment, except for the photoacoustic wave detection element  2   b.    
     When the photoacoustic wave detection element  2  is provided on the side surface of the photoacoustic guide wire  10  or  10   a  as in the first and second embodiments, the thickness of the photoacoustic guide wire  10  or  10   a  increases by the thickness of the photoacoustic wave detection element  2 . By providing the photoacoustic wave detection element  2   b  in the separate catheter  30  provided separately from the photoacoustic guide wire  10  as in the third embodiment, the diameter of the photoacoustic guide wire  10   b  that enters the occluded area C can be reduced. In particular, by providing the photoacoustic wave detection element  2   b  at the tip portion of the catheter  30 , the photoacoustic wave detection element  2   b  can be provided to face a direction in which the photoacoustic wave W is incident. As a result, the detection ability of the photoacoustic wave W can be improved. 
     When the use of the photoacoustic guide wire  10   b  ends, the photoacoustic guide wire  10   b  is accommodated in the catheter  30 . 
     When the photoacoustic wave W propagates not only due to the tissue of the occluded area C but also due to the blood B flowing into the crushed occluded area C. Accordingly, the photoacoustic guide wire  10   b  enters the tissue of the occluded area C, and even when the catheter  30  is present outside the occluded area C, the photoacoustic wave detection element  2   b  can receive the photoacoustic wave W. 
     The present invention is not limited to the embodiments and includes various modification examples. For example, the embodiments have been described in detail in order to easily describe the present invention, and the present invention is not necessarily to include all the configurations described above. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Further, the configuration of one embodiment can be added to the configuration of another embodiment. Also, addition, deletion, and replacement of another configuration can be made for a part of the configuration each of the embodiments. 
     In addition, some or all of the above-described configurations, functions, portions  111  to  116  and  111   a,  the storage device  130 , and the like may be realized by hardware, for example, by designing an integrated circuit. Also, as illustrated in  FIGS. 3 and 11 , the configurations, functions, and the like may be realized by software by a processor such as a CPU interpreting and executing a program that realizes each of the functions. Information such as a program, a table, or a file that realizes the functions can be stored not only in a hard disk (HD) but also in a storage device such as the memory  110  or a solid state drive (SSD) or in a storage medium such as an integrated circuit (IC) card, a secure digital (SD) card, or a digital versatile disc (DVD). 
     In addition, in each of the embodiments, the drawings illustrate control lines and information lines as considered necessary for explanations but do not illustrate all control lines or information lines in the products. It can be considered that almost of all components are actually interconnected.