Photoacoustic imaging apparatus and photoacoustic imaging method

Abstract

A photoacoustic imaging apparatus performs imaging of an optical absorber. The photoacoustic imaging apparatus includes a light source, a detector configured to detect an acoustic wave generated from the optical absorber that has absorbed energy of light emitted from the light source, and a signal processing unit configured to form an image of the optical absorber. The signal processing unit stores information indicating whether a rate of change in pressure of the acoustic wave detected by the detector is positive or negative before performing a waveform process on the acoustic wave.

1 . A photoacoustic imaging apparatus comprising:
 a light source;   a detector configured to detect an acoustic wave generated from an optical absorber that has absorbed energy of light emitted from the light source; and   a signal processing unit configured to form a signal of an image of the optical absorber,   wherein the signal processing unit stores information indicating whether a rate of change in pressure of the acoustic wave detected by the detector is positive or negative before performing a waveform process on the acoustic wave, determines whether the rate of change in pressure of the acoustic wave starts from positive or negative, and forms the signal of the image using a result of the determination.   
     
     
         2 . The photoacoustic imaging apparatus according to  claim 1 , wherein the waveform process is envelope detection. 
     
     
         3 . The photoacoustic imaging apparatus according to  claim 1 , wherein, in a case where the rate of change in pressure of the acoustic wave is negative at the start, the signal processing unit outputs a signal for displaying information indicating that the optical absorber has an optical absorption coefficient lower than an optical absorption coefficient of a surrounding region of the optical absorber. 
     
     
         4 . The photoacoustic imaging apparatus according to  claim 1 , wherein, in a case where the rate of change in pressure of the acoustic wave is negative at the start, the signal processing unit converts acoustic pressure information obtained through the waveform process from a positive value to a negative value or vice versa, and forms a signal of an image of the optical absorber on the basis of the converted acoustic pressure information. 
     
     
         5 . The photoacoustic imaging apparatus according to  claim 1 , wherein the detector is a focus transducer. 
     
     
         6 . The photoacoustic imaging apparatus according to  claim 3 , further comprising an image display unit,
 wherein the image display unit displays an image of an optical absorber having an optical absorption coefficient lower than an optical absorption coefficient of a surrounding region by using a display color different from a display color of the surrounding region or by using a color tone different from a color tone of the surrounding region.   
     
     
         7 . The photoacoustic imaging apparatus according to  claim 3 , further comprising an image display unit,
 wherein the image display unit displays an image of a tissue having an optical absorption coefficient lower than an optical absorption coefficient of a surrounding region, an identification symbol being added to the image.   
     
     
         8 . The photoacoustic imaging apparatus according to  claim 1 , wherein the signal processing unit performs correction in accordance with a frequency response of the detector on the acoustic wave detected by the detector before storing the information indicating whether the rate of change in pressure of the acoustic wave is positive or negative. 
     
     
         9 . The photoacoustic imaging apparatus according to  claim 1 ,
 wherein the light source is capable of emitting light having a first wavelength and light having a second wavelength that is different from the first wavelength, and   wherein the signal processing unit identifies the optical absorber by comparing a shape of a first acoustic wave obtained through irradiation with the light having the first wavelength with a shape of a second acoustic wave obtained through irradiation with the light having the second wavelength.   
     
     
         10 . A photoacoustic imaging method comprising:
 a step of emitting light from a light source;   a step of detecting an acoustic wave generated from an optical absorber that has absorbed energy of the light emitted from the light source;   a step of storing information indicating whether a rate of change in pressure of the detected acoustic wave is positive or negative before performing a waveform process on the acoustic wave; a step of determining whether the rate of change in pressure of the acoustic wave starts from positive or negative; and   a step of forming a signal of an image using a result of the determining step.