Research On Intravascular Photoacoustic Imaging And Spectrum Analysis For Detecting Atherosclerosis

Atherosclerosis has become a major threat to human health as a common cause of cardiovascular disease,which is often accompanied by vulnerable plaques.Therefore,it is of great significance to accurately detect vulnerable plaques with high resolution and high sensitivity imaging technology.Although an intravascular ultrasound(IVUS),which is a catheter-based intravascular imaging technique with good penetration depth and axial resolution,has been demonstrated to provide structural information of atherosclerotic plaque,the contrast between the lipid-rich region and other soft tissue is confined.To address this issue,intravascular photoacoustic(IVPA)imaging,combining the advantages of high ultrasonic resolution and strong optical absorption contrast,seems to be an alternative method to detect atherosclerotic plaque.However,traditional ultrasonic and photoacoustic imaging only use the amplitude information in the radio frequency(RF)echo signal,ignoring the frequency spectral information.As we know,the RF echo signal reflects the interaction of light /sound and tissue,and its spectrum contains a lot of information about tissue microstructure.Therefore,in this thesis,photoacoustic spectrum analysis of atherosclerosis RF signal was proposed to obtain the spectrum information and make the detection is more accurate.It shows that the spectrum analysis can identify the calcification area,lipid regions and normal tissue by spectral eigenvalue,which provides a new idea for the detection and evaluation of atherosclerosis in photoacoustic imaging.The main contents of this thesis are as follows: first,the KNN lead-free piezoelectric single crystal endoscopic photoacoustic probe,photoacoustic imaging system and the echo signal data acquisition were introduced;second,the RF signal spectrum analysis and t-test of spectral eigenvalue were used to characterize different region of atherosclerosis;finally,the comparison between the photoacoustic spectrum analysis and virtual histologyintravascular ultrasound(VH-IVUS)was carried out.As a result,the spectrum of photoacoustic RF signal can not only distinguish between the calcification area and lipid,but also can recognize the heavy degree of calcification and mild calcification.Thus,it suggests that spectral analysis of photoacoustic signals behaves the similar performance as VH-IVUS to detect atherosclerosis,and have better identification.