Wearable Ultrasound
The proven safety of ultrasound and its efficacy in soft-tissue imaging, along with the ability to integrate complex and large imaging systems into a compact system-on-chip using CMOS has enabled the development of portable ultrasound imaging devices for point-of-care use. We are developing an ultrasound imaging ASIC composed of a pitch-matched transceiver array mated to a 32×32 element 2-D transducer array made of composite PZT. This device is packaged into a flexible, compact and bio-compatible form factor which obviates the need for bulky and expensive ultrasonic imaging platforms while the patch-like form factor also allows for use in continuous monitoring. The 2-D transducer array enables the device to perform volumetric imaging while remaining stationary over the tissue. The device has in-pixel transmitters and programmability to allow high-frame imaging and performs 16-fold channel count reduction using micro-beamforming. Previous work in this area involved a flexible, surface-conforming transducer array and a 2-D phased ultrasound transmitter with integrated PZT.
Selected Publications
Jagannaath Shiva Letchumanan, Siddhesh Gandhi, Heyu Yin, Aditya Ramkumar, Kenneth L. Shepard.
A Mechanically Flexible 32-by-32-Element Pitch-Matched Ultrasound Front-End Transceiver with Two-Stage Beamforming for 3D Imaging
2024 IEEE Custom Integrated Circuits Conference (CICC).
(May 2024)
[Article]
Abstract
CMOS integration creates the possibility of rendering complex imaging systems into low-cost wearable form factors with the potential to transform medicine through continuous monitoring in a point-of-care setting. The proven safety of ultrasound, its efficacy in soft-tissue imaging, and the integration of electronic systems-on-chip have independently led to the development of active front-end ASICs for handheld ultrasound systems [1]–[4] and passive mechanically flexible 2D transducer arrays tethered to large external electronics [5]. In this work, through innovation in design and packaging, we combine these approaches to produce a mechanically flexible 2D 1024-element 5-MHz wearable ultrasound device (Fig. 1) with a focal depth of up to 3.5 cm that conforms to the surface of the body.
Elloian, J., Jadwiszczak, J., Arslan, V. et al..
Flexible ultrasound transceiver array for non-invasive surface-conformable imaging enabled by geometric phase correction
Sci Rep. 12, 16184
(Sep 2022)
[Article]
Abstract
Ultrasound imaging provides the means for non-invasive real-time diagnostics of the internal structure of soft tissue in living organisms. However, the majority of commercially available ultrasonic transducers have rigid interfaces which cannot conform to highly-curved surfaces. These geometric limitations can introduce a signal-quenching air gap for certain topographies, rendering accurate imaging difficult or impractical. Here, we demonstrate a 256-element flexible two-dimensional (2D) ultrasound piezoelectric transducer array with geometric phase correction. We show surface-conformable real-time B-mode imaging, down to an extreme radius of curvature of 1.5 cm, while maintaining desirable performance metrics such as high signal-to-noise ratio (SNR) and minimal elemental cross-talk at all stages of bending. We benchmark the array capabilities by resolving reflectors buried at known locations in a medical-grade tissue phantom, and demonstrate how phase correction can improve image reconstruction on curved surfaces. With the current array design, we achieve an axial resolution of ≈ 2 mm at clinically-relevant depths in tissue, while operating the array at 1.4 MHz with a bandwidth of ≈ 41%. We use our prototype to image the surface of the human humerus at different positions along the arm, demonstrating proof-of-concept applicability for real-time diagnostics using phase-corrected flexible ultrasound probes.
T. Costa, C. Shi, K. Tien, J. Elloian, F. A. Cardoso and K. L. Shepard.
An Integrated 2D Ultrasound Phased Array Transmitter in CMOS With Pixel Pitch-Matched Beamforming
IEEE Transactions on Biomedical Circuits and Systems. vol. 15, no. 4, pp. 731-742, Aug. 2021
(Aug 2021)
[Article]
Abstract
Emerging non-imaging ultrasound applications, such as ultrasonic wireless power delivery to implantable devices and ultrasound neuromodulation, require wearable form factors, millisecond-range pulse durations and focal spot diameters approaching 100 μm with electronic control of its three-dimensional location. None of these are compatible with typical handheld linear array ultrasound imaging probes. In this work, we present a 4 mm × 5 mm 2D ultrasound phased array transmitter with integrated piezoelectric ultrasound transducers on complementary metal-oxide-semiconductor (CMOS) integrated circuits, featuring pixel-level pitch-matched transmit beamforming circuits which support arbitrary pulse duration. Our direct integration method enabled up to 10 MHz ultrasound arrays in a patch form-factor, leading to focal spot diameter of ∼200 μm, while pixel pitch-matched beamforming allowed for precise three-dimensional positioning of the ultrasound focal spot. Our device has the potential to provide a high-spatial resolution and wearable interface to both powering of highly-miniaturized implantable devices and ultrasound neuromodulation.
