Real-Time Coded Excitation Imaging Using a CMUT-Based Side Looking Array for Intravascular Ultrasound.

Intravascular ultrasound (IVUS) is a well-established diagnostic method that provides images of the vessel wall and atherosclerotic plaques. We investigate the potential for phased-array IVUS utilizing coded excitation (CE) for improving the penetration depth and image signal-to-noise ratio (SNR). It is realized on a new experimental broadband capacitive micromachined ultrasound transducer (CMUT) array, operated in collapse mode, with 96 elements placed at the circumference of a catheter tip with a 1.2- mm diameter. We characterized the array performance for CE imaging and showed that the -6-dB device bandwidth at a 30-V dc biasing is 25 MHz with a 20-MHz center frequency, with a transmit sensitivity of 37 kPa/V at that frequency. We designed a linear frequency modulation code to improve penetration depth by compensating for high-frequency attenuation while preserving resolution by a mismatched filter reconstruction. We imaged a wire phantom and a human coronary artery plaque. By assessing the image quality of the reconstructed wire phantom image, we achieved 60- and 70- µm axial resolutions using the short pulse and coded signal, respectively, and gained 8 dB in SNR for CE. Our developed system shows 20-frames/s, pixel-based beam-formed, real-time IVUS images.

In vivo intravascular photoacoustic imaging of plaque lipid in coronary atherosclerosis.

Prospective identification of lipid-rich vulnerable plaque has remained an elusive goal. Intravascular photoacoustics, a hybrid optical and ultrasonic technology, was developed as a tool for lipid-rich plaque imaging. Here, we present the first in vivo images of lipid-rich coronary atherosclerosis acquired with this new technology in a large animal model, and relate them to independent catheter-based imaging and histology.

A 2-D Ultrasound Transducer With Front-End ASIC and Low Cable Count for 3-D Forward-Looking Intravascular Imaging: Performance and Characterization.

Intravascular ultrasound (IVUS) is an imaging modality used to visualize atherosclerosis from within the inner lumen of human arteries. Complex lesions like chronic total occlusions require forward-looking IVUS (FL-IVUS), instead of the conventional side-looking geometry. Volumetric imaging can be achieved with 2-D array transducers, which present major challenges in reducing cable count and device integration. In this work, we present an 80-element lead zirconium titanate matrix ultrasound transducer for FL-IVUS imaging with a front-end application-specific integrated circuit (ASIC) requiring only four cables. After investigating optimal transducer designs, we fabricated the matrix transducer consisting of 16 transmit (TX) and 64 receive (RX) elements arranged on top of an ASIC having an outer diameter of 1.5 mm and a central hole of 0.5 mm for a guidewire. We modeled the transducer using finite-element analysis and compared the simulation results to the values obtained through acoustic measurements. The TX elements showed uniform behavior with a center frequency of 14 MHz, a -3-dB bandwidth of 44%, and a transmit sensitivity of 0.4 kPa/V at 6 mm. The RX elements showed center frequency and bandwidth similar to the TX elements, with an estimated receive sensitivity of /Pa. We successfully acquired a 3-D FL image of three spherical reflectors in water using delay-and-sum beamforming and the coherence factor method. Full synthetic-aperture acquisition can be achieved with frame rates on the order of 100 Hz. The acoustic characterization and the initial imaging results show the potential of the proposed transducer to achieve 3-D FL-IVUS imaging.