High-Repetition Rate Laser for Real-Time and 3D Photoacoustic Imaging

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Photoacoustic (PA) imaging is a novel imaging technique that takes the advantages of both optical and ultrasound (US) imaging. Upon absorbing a high energy laser pulse, tissue experiences a rapid and localized heating. The tissue undergoes thermoelastic expansion which generates US waves. The waves propagate towards the tissue surface where they are detected by an US transducer array. PA imaging can image up to a few centimeters into tissue, much deeper than any other optical imaging techniques. Furthermore, PA imaging can detect blood vessels, and quantify blood oxygen saturation and hypoxia, which are highly specific biomarkers of cancer. Thus, PA imaging can augment classical US by adding functional imaging of cancer specific absorption contrasts. Here we propose to develop real-time and 3D photoacoustic tomography (PAT) for detecting prostate and breast cancers. ******Built upon our previous CHRP and CRD grants, a prototype PAT system has been developed for cancer imaging. We have developed an optical fiber catheter to deliver high energy and uniform laser illumination to the prostate through the urethra. An optimum US transducer scanning and detecting geometry has been developed for prostate imaging. Up to 4 cm imaging depth has been demonstrated in ex vivo tissues. For breast cancer imaging, an automated breast ultrasound scanner was used to acquire PAT images. We found that by adding PAT to multi-parametric US can offer a powerful set of metrics for the diagnosis and staging of breast cancer. However, the laser we used before only has 10 Hz repetition rate which is too slow. This has limited the capability of the PAT system to obtain only static images of tissue. For clinical applications, real-time PAT imaging at a speed comparable to US at hundreds of Hertz is needed in order to monitor dynamic changes and overcome motion artifacts. For 3D PAT, hundreds of laser shots are needed in order to acquire PA signals from a 3D volume.******In this application, a laser with fast 100 Hz repetition rate is requested. We propose to develop real-time and 3D PAT for detecting prostate and breast cancers. We will also develop custom PAT/US imagining probes by novel capacitive micromachined ultrasonic transducer (CMUT) arrays that are uniquely large, flexible, and transparent. We will also extend our image analysis approaches from US imaging to PAT. The proposed research program will make major advances in medical imaging by enhancing the capability of US based imaging. By adding the blood absorption and oxygen saturation contrasts from PAT to our multi-parametric US that includes B-mode, elastography, time series, and Doppler, it is expected to greatly enhance the specificity and sensitivity of cancer detection. We will produce and engineer specific techniques of PAT imaging and translate the techniques to clinical applications on prostate and breast cancer imaging. PAT/US imaging will have great potential to improve cancer detection and treatment outcome.