Advanced Polymeric Tissue-Mimicking Materials and Phantoms for Evaluation of Multispectral Photoacoustic Imaging Systems

University Of California-San Diego, La Jolla CA

Investigators

Abstract

NON-TECHNICAL SUMMARY Ultrasound is a powerful tool to image diseases including cancer, orthopedic disorders, and heart function. One limitation of ultrasound is that it suffers from low contrast between the region of interest versus the background tissue. Therefore, there is a wide body of research into a special kind of ultrasound known as photoacoustic imaging. Photoacoustic imaging uses light to generate sound only in the area of interest. This increases the contrast. Unfortunately, photoacoustic ultrasound is not yet approved for widespread use in people. This might be partially due to a lack of standardization devices and methods to validate the novel imaging equipment that is needed for photoacoustic imaging. Therefore, this proposed work will create specialized plastic objects with known optical and acoustic properties suitable for calibrating and standardizing photoacoustic imaging equipment. This proposal combines expertise from academia and the Food and Drug Administration to create test objects and methods that will be useful to instrument manufacturers and physicians. The resulting test objects will improve knowledge of how to best create photoacoustic imaging instrumentation and might also streamline regulatory approval of this equipment. In turn, this will increase patient access to this important imaging technique to ultimately advance the national health and quality of life. TECHNICAL SUMMARY Photoacoustic imaging provides deep tissue imaging similar to ultrasound but with enhanced optical contrast and additional functional and molecular imaging capabilities. However, no standardized performance test methods or phantoms exist for photoacoustic imaging system evaluation unlike mature techniques (ultrasound, MRI, CT). The fundamental limitation is a lack of materials to simultaneously simulate tissue properties over a broad range of optical wavelengths and acoustic frequencies. This leaves investigators, instrument manufacturers, and regulatory agencies without clear strategies to evaluate device safety and effectiveness. This proposed work will create stable, biologically relevant imaging phantoms with well-characterized optical absorption/scattering coefficients, acoustic impedance, etc. that broadly simulate tissue over a wide range of optical wavelengths and acoustic frequencies. A literature search and laboratory study will identify suitable materials such as polyacrylamide hydrogels or novel polyvinyl chloride plastisol formulations. Intrinsic properties will be measured using well-validated spectrophotometry and acoustic pulse transmission methods and equipment at FDA. Once the phantom material formulations have been optimized, we will construct phantoms in several specific configurations to evaluate image quality metrics such as spatial resolution, penetration depth, etc. These novel phantoms will then be used with three photoacoustic systems with substantially different operating parameter ranges (e.g. optical wavelengths). Image quality metrics will be compared between devices to elucidate performance trade-offs between systems and the overall impact of system design choices and phantom properties on performance. The goal is to produce phantoms with 6-month stability that spectrally mimic hemoglobin and deoxyhemoglobin and contain targets that enable image quality testing. The outcome will be a well-validated tissue-mimicking phantom to support device developers and inform regulatory decision-making including use as potential FDA Medical Device Development Tools. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.