Advanced Devices for Photoacoustic Imaging to Improve Cancer and Cerebrovascular Medicine

Abstract

Recent clinical studies have demonstrated that photoacoustic imaging (PAI) provides important diagnostic information for breast cancer staging. Despite these promising studies, PAI remains an unfeasible option for clinics due to the cost to implement, the required large modification in user conduct and the inflexibility of the hardware to accommodate other applications for the incremental enhancement in diagnostic information. The research described in this dissertation addresses these issues by designing attachments to clinical ultrasound probes and incorporating custom detectors into commercial ultrasound scanners. The ultimate benefit of these handheld devices is to expand the capability of current ultrasound systems and facilitate the translation of PAI to enhance cancer diagnostics and neurosurgical outcomes. Photoacoustic enabling devices (PEDs) were designed as attachments to two clinical ultrasound probes optimized for breast cancer diagnostics. PAI uses pulsed laser excitation to create transient heating (<1°C) and thermoelastic expansion that is detected as an ultrasonic emission. These ultrasonic emissions are remotely sensed to construct noninvasive images with optical contrast at depths much greater than other optical modalities. The PEDs are feasible in terms of cost, user familiarity and flexibility for various applications. Another possible application for PAI is in assisting neurosurgeons treating aneurysms. Aneurysms are often treated by placing a clip to prevent blood flow into the aneurysm. However, this procedure has risks associated with damaging nearby vessels. One of the developed PEDs demonstrated the feasibility to three-dimensionally image tiny microvasculature (<0.3mm) beyond large blood occlusions (>2.4mm) in a phantom model. The capability to use this during surgery would suggest decreasing the risks associated with these treatments. However, clinical ultrasound arrays are not clinically feasible for microsurgical applications due to their bulky size and linear scanning requirements for 3D. Therefore, capacitive micromachined ultrasound transducer (CMUT) two-dimensional arrays compatible with standard ultrasound scanners were used to generate real-time 3D photoacoustic images. Future probes, designed incorporating CMUT arrays, would be relatively simple to fabricate and a convenient upgrade to existing clinical ultrasound equipment. Eventually, a handheld tool with the ability to visualize, in real-time 3D, the desired microvasculature, would assist surgical procedures. The potential implications of PAI devices compatible with standard ultrasound equipment would be a streamlined cost efficient solution for translating photoacoustics into clinical practice. The practitioner could then explore the benefits of the enhanced contrast adjunctive to current ultrasound applications. Clinical availability of PAI could enhance breast cancer diagnostics and cerebrovascular surgical outcomes.