MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications

Abstract

Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given.

The Application of Prussian Blue Nanoparticles in Tumor Diagnosis and Treatment

“…The photoacoustic imaging (PAI) technique is a broadly applicable noninvasive imaging modality; transient acoustic waves are generated via the absorption of NIR in biological tissues, which can then be detected using a traditional ultrasound transducer [77][78][79][80]. PAI has numerous advantages including a high spatial resolution, strong contrast, noninvasiveness, real-time imaging, low cost, and the ability for both endogenous and exogenous imaging, which has attracted wide attention for applications involving the imaging of biological tissues [44].…”

Perspective on fast-evolving photoacoustic tomography

“… 22 In particular, low-cost light sources such as laser diodes and light emitting diodes can significantly reduce the system cost of both PAM and PACT, and accelerate the technical translation to clinical practice. The success of commercial PAT products will in turn provide strong incentives for key industrial partners to develop products that are specially optimized for PAT, such as high-power, high-speed lasers with relaxed coherence; low-cost CMUT or PMUT arrays with a large number of elements; 30 high-channel-number, high-speed data acquisition systems with built-in amplification capability; and high-speed GPU systems with large on-chip memory. Enabled by these updated system components, which are often the bottlenecks in PAT technology, the next wave of technological breakthroughs will naturally follow, including (i) real-time volumetric PACT systems for human imaging, such as breast cancer screening; (ii) high-speed, high-resolution PAM of neuronal activities enabled by novel voltage- or calcium-sensitive PA probes; (iii) highly-compact endoscopic and intravascular PAT enabled by optical ultrasound sensors; (iv) single-organelle or single-molecule PA imaging enabled by super-resolution mechanisms; (v) large-scale, high-speed 3D modeling of PA signal generation and propagation in a complex system; and (vi) robust quantitative PAT of tissue functions and molecular compositions enabled by deep learning approaches.…”

“…Limited by space, we will focus on several important developments that have overcome the longstanding limits in traditional PAT. Interested readers are referred to comprehensive review articles that provide in-depth analyses and discussions on low-cost light sources, 22 , 26 – 28 novel ultrasound sensors, 21 , 29 , 30 PA contrast agents, 29 , 31 , 32 PA endoscopy, 33 , 34 deep learning enhanced PAT, 35 – 37 as well as clinical translation of PAT. 22 , 38 – 41 …”

Advances in Endoscopic Photoacoustic Imaging

“…Apart from the above conventional piezoelectric materials and their composites, new materials and technologies are emerging in PA/US endoscopy, including lead free piezoelectric materials [80], micromachine based US transducers (piezoelectric and capacitive micromachined US transducer, PMUT and CMUT) [81][82][83][84][85][86], and optical based acoustic sensing [87]. They have their own unique advantages, but further developments are still required to prove their practical capabilities in PA/US endoscopy.…”