An FPGA-Based Backend System for Intravascular Photoacoustic and Ultrasound Imaging

Dual-modal Photoacoustic and Ultrasound Imaging: from preclinical to clinical applications

Photoacoustic imaging is a novel biomedical imaging modality that has emerged over the recent decades. Due to the conversion of optical energy into the acoustic wave, photoacoustic imaging offers high-resolution imaging in depth beyond the optical diffusion limit. Photoacoustic imaging is frequently used in conjunction with ultrasound as a hybrid modality. The combination enables the acquisition of both optical and acoustic contrasts of tissue, providing functional, structural, molecular, and vascular information within the same field of view. In this review, we first described the principles of various photoacoustic and ultrasound imaging techniques and then classified the dual-modal imaging systems based on their preclinical and clinical imaging applications. The advantages of dual-modal imaging were thoroughly analyzed. Finally, the review ends with a critical discussion of existing developments and a look toward the future.

Hardware Architectures for Real-Time Medical Imaging

Medical imaging is considered one of the most important advances in the history of medicine and has become an essential part of the diagnosis and treatment of patients. Earlier prediction and treatment have been driving the acquisition of higher image resolutions as well as the fusion of different modalities, raising the need for sophisticated hardware and software systems for medical image registration, storage, analysis, and processing. In this scenario and given the new clinical pipelines and the huge clinical burden of hospitals, these systems are often required to provide both highly accurate and real-time processing of large amounts of imaging data. Additionally, lowering the prices of each part of imaging equipment, as well as its development and implementation, and increasing their lifespan is crucial to minimize the cost and lead to more accessible healthcare. This paper focuses on the evolution and the application of different hardware architectures (namely, CPU, GPU, DSP, FPGA, and ASIC) in medical imaging through various specific examples and discussing different options depending on the specific application. The main purpose is to provide a general introduction to hardware acceleration techniques for medical imaging researchers and developers who need to accelerate their implementations.

Investigation on Design Theory and Performance Analysis of Vacuum Capacitive Micromachined Ultrasonic Transducer

The capacitive micromachined ultrasonic transducer (CMUT), as a new acoustic-electric conversion element, has a promising application prospect. In this paper, the structure of the vacuum capacitive micromachined ultrasonic transducer is presented, and its performance-influencing factors are investigated. Firstly, the influencing factors of the performance parameters of the vacuum CMUT are analyzed theoretically based on the circular plate model and flat plate capacitance model, and the design principles of the structural parameters of the CMUT cell are proposed. Then, the finite element simulation software COMSOL Multiphysics is used to construct CMUT cell models with different membrane materials, membrane shapes, membrane radius thicknesses, and cavity heights for simulation verification. The results show that both the membrane parameters and the cavity heights affect the performance parameters of the Vacuum CMUT. In order to improve the efficiency of the CMUT, materials with low bending stiffness should be selected, and the filling factor of the membrane should be increased. In order to achieve high-transmission sound pressure, a smaller radius thickness and a larger cavity height should be selected. To achieve high reception sensitivity, a larger membrane radius thickness and a smaller cavity height should be selected. In order to obtain high fractional bandwidth, a larger membrane radius thickness should be selected. The results of this paper provide a basis for the design of Vacuum CMUT cell structure.

An Improved CMUT Structure Enabling Release and Collapse of the Plate in the Same Tx/Rx Cycle for Dual-Frequency Acoustic Angiography

This study demonstrates, in detail, the potential of using capacitive micromachined ultrasonic transducers (CMUTs) for acoustic angiography of the microvasculature. It is known that when ultrasound contrast agents (microbubbles) are excited with moderate acoustic pressure around their resonance (2-4 MHz), they produce higher order harmonics (greater than third harmonic) due to their nonlinear behavior. To date, the fundamental challenge has been the availability of a transducer that can generate the transmit signals to excite the microbubbles at low frequencies and, in the same cycle, confocally detect harmonics in the higher frequencies. We present a novel device structure and dual-mode operation of a CMUT that operates with a center frequency of 4.3 MHz and 150% bandwidth in the conventional mode for transmitting and a center frequency of 9.8 MHz and a 125.5% bandwidth in collapse mode for receiving. Output pressure of 1.7 MPapp is achieved on the surface of a single unfocused transducer. The mechanical index at the transducer surface is 0.56. FEM simulations are performed first to show the functionality of the proposed device, and then, the device fabrication is described in detail. Finally, we experimentally demonstrate the ability to detect the microbubble signals with good contrast, and the background reflection is adequately suppressed, indicating the feasibility of the presented approach for acoustic angiography.

Design, Development, and Multi-Characterization of an Integrated Clinical Transrectal Ultrasound and Photoacoustic Device for Human Prostate Imaging

The standard diagnostic procedure for prostate cancer (PCa) is transrectal ultrasound (TRUS)-guided needle biopsy. However, due to the low sensitivity of TRUS to cancerous tissue in the prostate, small yet clinically significant tumors can be missed. Magnetic resonance imaging (MRI) with TRUS fusion biopsy has recently been introduced as a way to improve the identification of clinically significant PCa in men. However, the spatial errors in coregistering the preprocedural MRI with the real-time TRUS causes false negatives. A real-time and intraprocedural imaging modality that can sensitively detect PCa tumors and, more importantly, differentiate aggressive from nonaggressive tumors could largely improve the guidance of biopsy sampling to improve diagnostic accuracy and patient risk stratification. In this work, we seek to fill this long-standing gap in clinical diagnosis of PCa via the development of a dual-modality imaging device that integrates the emerging photoacoustic imaging (PAI) technique with the established TRUS for improved guidance of PCa needle biopsy. Unlike previously published studies on the integration of TRUS with PAI capabilities, this work introduces a novel approach for integrating a focused light delivery mechanism with a clinical-grade commercial TRUS probe, while assuring much-needed ease of operation in the transrectal space. We further present the clinical potential of our device by (i) performing rigorous characterization studies, (ii) examining the acoustic and optical safety parameters for human prostate imaging, and (iii) demonstrating the structural and functional imaging capabilities using deep-tissue-mimicking phantoms. Our TRUSPA experimental studies demonstrated a field-of-view in the range of 130 to 150 degrees and spatial resolutions in the range of 300 μm to 400 μm at a soft tissue imaging depth of 5 cm.

Single-Shot Near-Field Volumetric Imaging System for Optical Ultrasound and Photoacoustics Using Capacitive Micromachined Ultrasonic Transducer Without Transmission Mode

In this article, we present a single-shot dual-mode imaging system that uses optical ultrasound (US) as an ultrasonic pulser without a transmission circuit. The ultrasonic pulse-echo system comprises an optical US pulser generated by carbon nanotubes (CNTs), which generate a high-power photoacoustic (PA) signal and a capacitive micromachined ultrasonic transducer (CMUT) receiver. By fabricating a thin CNT-polydimethylsiloxane (PDMS) composite capable of semiabsorption of the laser, a single-shot imaging system was developed. By transmitting a semipenetration light to the object, US and PA imaging were performed in a single shot. A CNT thickness of [Formula: see text] produced a maximum pressure of 154 kPa, and US was received by CMUT with a 2-MHz center frequency in PDMS. Additionally, a low-profile and near-depth imaging system was constructed with an intermediate layer of the 6-mm PDMS for the dry contact method. We performed a single-shot dual-mode imaging experiment on point and line phantoms, as well as the particle spread in the soft tissue. Thus, we examined the feasibility of the near-depth and single-shot dual-mode (US and PA) imaging system capable of a dry contact.

Photoacoustic imaging for guidance of interventions in cardiovascular medicine

Imaging guidance is paramount to procedural success in minimally invasive interventions. Catheter-based therapies are the standard of care in the treatment of many cardiac disorders, including coronary artery disease, structural heart disease and electrophysiological conditions. Many of these diseases are caused by, or effect, a change in vasculature or cardiac tissue composition, which can potentially be detected by photoacoustic imaging. This review summarizes the state of the art in photoacoustic imaging approaches that have been proposed for intervention guidance in cardiovascular care. All of these techniques are currently in the preclinical phase. We will conclude with an outlook towards clinical applications.