A real-time electronic beamformer for high-resolution ultrasound imaging of the Cochlea

Low-frequency (< 20 MHz) ultrasound (LFUS) is one of the most common imaging modalities in diagnostic medicine, primarily because it is safe, reliable, and real-time. In contrast, high-frequency (>20MHz) ultrasound (HFUS) imaging is a relatively new technique, with an order of magnitude better image resolution compared to low-frequency systems. Despite the improved resolution, HFUS systems are not routinely used in clinical practice. The main barrier preventing their adoption is that until recently, these systems were based on single-element geometrically focused transducers that produced images with a limited depth-of-field and slow frame-rate. In LFUS systems, drastic improvements in both frame-rate and depth-of-field have been achieved by replacing the single-element transducer with a transducer array and an electronic beamformer. This allows electronic focusing at a wide range of depths within the tissue and increased frame-rates. Consequently, there has been a great deal of interest in developing array-based systems for HFUS. Unfortunately, fabricating high-frequency arrays and their associated beamformers is extremely difficult. In particular, to produce a tightly collimated ultrasound beam at these very short wavelengths, array elements with microscopic dimensions are required. In addition, the high frequencies require that the digital sampling resolution of the electronic beamformer and speed of parallel signal processing be greatly increased. In 2009, the world's first commercially available HFUS array-based system was released. The arrays for this system, however, are designed for use in topical applications in which relatively large apertures and packaging are of no concern. We are developing a much smaller HFUS array in an endoscopic form factor, specifically for imaging sub-surface structures of the ear via the ear canal. This proposal seeks infrastructure funding for a real-time 50 MHz digital beamformer. This will allow us to generate real-time images using the custom 50 MHz array endoscopes that we are currently developing using our recently established micro-fabrication facility. Real-time imaging capabilities with Doppler velocimetry are essential to furthering our understanding of inner-ear dynamics.