This Small Business Innovation Research (SBIR) Phase I project focuses on the development of a new photoacoustic imaging system that cascades a miniature infrared light source behind an infrared-transparent capacitive micromachined transducer (CMUT) array, and illuminates the image target through the CMUT array. The unique features of this illumination-through-transducer design are in that 1) there is no need for external alignment mechanisms between the transducer and the light source during image acquisition, 2) depth at which the tissue can be imaged is increased to 10 cm, and 3) overall size of the integrated imager head is significantly reduced with the cascaded structure. Key objectives of this research include design, modeling, fabrication, packaging and testing of of a Capacitive Micromachined Ultrasonic Transducer (CMUT) array that is transparent to near infrared (NIR) illumination. We anticipate to successfully demonstrate the functionality and the feasibility of integration of this CMUT array in a cascaded light-source-to-CMUT PAI system. This system will be used for breast and other type of cancers screening. The proposed PAI system will be an enabling technology platform for medical imaging, diagnosis and monitoring.
The broader impact/commercial potential of this project lies in that the technology developed here can be applied outside of the proposed photo acoustic imaging applications in clinical settings. Initially, this technology will leverage some of the existing hardware profile of the traditional ultrasound systems, to result in a safe, portable, low cost medical imaging device for screening and early detection of breast and other cancers. While optical microscopy continues to evolve through integration of optics with microfluidics for diagnostic applications, it still has limitations such as lack of portability and high cost due to complex and expensive optical components. With proposed technology, multiple detection and imaging modalities can be integrated for on-chip detection of infectious disease, as an alternative to optical microscopy. Moreover, the proposed system can be used as a light-to-mechanical and/or mechanical-to-light energy transducer in combination with microfluidics, to enable a range of point-of-care diagnostics and monitoring applications. The proposed technology can be combined with other emerging technology platforms including optofluidics and acustofluidics, to enable more functionality in smaller devices and at lower cost, for mobile-based clinical microscopy in a range of global healthcare applications.
The overall objective of this SBIR Project Phase I was to develop a novel Capacitive Micromachined Ultrasonic Transducer (CMUT) device that is transparent to near infrared (NIR) illumination and can be subsequently integrated in Phase II with electronics and optics into a compact photoacoustic imaging system for point of care diagnostics and treatment monitoring. This arrangement allows the light illumination to be focused through the detector, thus eliminating the need for external alignment mechanisms and increasing the depth at which the tissue can be imaged to up to 10 cm. The unique features of this illumination-through-transducer design are 1) no alignment or co-registration between the transducer and the light source needed, 2) reduced image acquisition time, and 3) small size of the imager head. This architecture works for both 1-D and 2-D CMUT arrays and is useful both for handheld units and endoscope applications. This will be an enabling technology for medical imaging, and a new tool at the physician's disposal for enabling earlier detection of cancers, for instance in patients presenting for routine annual physical exams. Phase I efforts had entirely focused on the CMUT development because the NIR transparency of this component is absolutely critical for the proposed photoacoustic system. Project Phase I consisted of three major tasks: modeling and design, process development and device fabrication, and packaging and test. In order to achieve consistent yield and device performance in manufacturing, we developed a glass based CMUT design utilizing glass as a transparent substrate. Glass was selected for its very high transmission efficiency. The thermal coefficient of expansion was optimized for the substrate and other materials used in the process. A photoacoustic image acquisition was successfully demonstrated with NIR transparent CMUT devices. Based upon the successfull proof of concept established in Phase I, this technology will be considered for broader potential advantages: due to its compact size this system can be used in combination with micofluidics, nano-optics and other enabling technologies, as a versatile energy transducer, to enable a range of diagnostic and monitoring applications at the point of care. There are potentially significant commercial and societal benefits of this technology in that it will satisfy an existing and growing market demand while improving patient outcomes.
