Study Of The Photoacoustic Imaging System Based On An Acoustic Lens And The Peak-hold Technology

Photoacoustic (PA) tomography, based on the intrinsic opticalabsorption properties of tissue, is a medical imaging technology. Thistechnology combines the merits of both pure ultrasound imaging andpure optical imaging, and it can provide high ultrasonic resolution andhigh optical contrast tissue images. Light absorption in the biologictissue is in close relation to its physical characteristics, metabolism andpathological status, etc. For this, PA imaging technology can be used forthe structure and function imaging of biological tissue and this methodhas become an active research area in recent years. And this technologymay be developed to a novel noninvasive medical imaging. A PAtomography technique, which based on an acoustic lens and thepeak-hold technique, is presented in this paper. This PA imaging systemenjoys the advantages of forming real-time imaging and acquiring thePA images more rapidly without any complex algorithms, and it mayprovide a more convenient method for future in vivo noninvasiveimaging of tissues and clinic diagnosis. Main contents of this paper areas follows:1. According to Fourier imaging theory, an acoustic lens withimaging ability can directly form the image of the PA signals generatedfrom the sample on the imaging plane. The PA signal enjoys theadvantage of time resolution, and the tomography images can beobtained by the time-resolved technique and the peak-hold technology.2. A peak detection-and-hold circuit is developed to acquire the peakvalue of the PA signal for the image reconstruction. The comprising, theworking principle, and the application in the PA imaging of the peakdetection-and-hold circuit are discussed. The anti-interference abilityand the imaging rate are improved, since the peak-hold technique isused. And the imaging system is simplified.3. According to acoustic lens imaging theory and the peak-holdtechnique, a fast PA imaging system is developed in this paper. Thehardware composing and the working principles of this system are discussed.4. The two dimensional image of the sample on a single layer andthe tomography images of the sample on different layers are obtained byusing the PA imaging system. And the PA tomography images areachieved successfully using the 4f acoustic lens PA imaging system. Theresults show that the images reconstructed in this experiment agree wellwith the original samples.When a short laser pulse illuminates the sample, the sample willgenerate ultrasound signals which are linearly proportional to theoptical absorption of the sample. By utilizing an acoustic lens, the PAsignals generated from the sample are directly imaged on the imagingplane and collected by the 64-element linear transducer array whichchanges the PA signals into the corresponding electronic signals. Thenthe electronic signals are converted into a one dimensional (1D) imageusing the peak detection-and-hold circuit. After vertical scanning with astep motor on the imaging plane, the 2D PA image of the sample isachieved successful. According to the imaging principle of acoustic lens,the PA signals generated from the sample on a plane require the samedelay time to reach the image plane, and the signals from differentplanes require different delay time to reach the same detected plane. Byusing the delay control technique of the peak-detection-and hold circuit,the PA images of the sample on different planes can be obtained bychanging the delay time of the peak detection-and-hold circuit. The PAtomography images of the sample on different planes are obtainedsuccessfully in this experiment. The images are vivid and contrastclearly with their backgrounds.