3D synthetic aperture imaging with a therapeutic spherical random phased array for transcostal applications

Abstract

Experimental validation of a synthetic aperture imaging technique using a therapeutic random phased array is described, demonstrating the dual nature of imaging and therapy of such an array. The transducer is capable of generating both continuous wave high intensity beams for ablating the tumor and low intensity ultrasound pulses to image the target area. Pulse-echo data is collected from the elements of the phased array to obtain B-mode images of the targets. Since therapeutic arrays are optimized for therapy only with concave apertures having low f-number and large directive elements often coarsely sampled, imaging can not be performed using conventional beamforming. We show that synthetic aperture imaging is capable of processing the acquired RF data to obtain images of the field of interest. Simulations were performed to compare different synthetic aperture imaging techniques to identify the best algorithm in terms of spatial resolution. Experimental validation was performed using a 1 MHz, 256-elements, spherical random phased array with 130 mm radius of curvature. The array was integrated with a research ultrasound scanner via custom connectors to acquire raw RF data for variety of targets. Imaging was implemented using synthetic aperture beamforming to produce images of a rib phantom and ex vivo ribs. The array was shown to resolve spherical targets within ±15 mm of either side of the axis in the focal plane and obtain 3D images of the rib phantom up to ±40 mm of either side of the central axis and at a depth of 3–9 cm from the array surface. The lateral and axial full width half maximum was 1.15 mm and 2.75 mm, respectively. This study was undertaken to emphasize that both therapy and image guidance with a therapeutic random phased array is possible and such a system has the potential to address some major limitations in the existing high intensity focused ultrasound (HIFU) systems. The 3D images obtained with a therapeutic array can be used to identify and locate strong scattering objects aiding to image guidance and treatment planning of the HIFU procedure.

Calculating the Effect of Ribs on the Focus Quality of a Therapeutic Spherical Random Phased Array

“…Preliminary investigations to customize the acoustic field of a 256-elements random phased array to enable ablation of liver was previously demonstrated by our group [22]. We have also demonstrated the dual nature of imaging and therapy of the spherical random phased array, thus providing a platform to image the strong aberrating structures such as rib cage in real time and tailor the acoustic field to achieve high peak focal intensity while avoiding heating of the ribs [21]. Ribs in the HIFU beam path not only get heated, due to their high absorption capabilities, leading to skin burns, but can also distort the focus quality significantly by generating secondary hotspots which may be harmful to the adjacent healthy tissue and critical structures.…”

“…The array transducer (Imasonics, Vorayr surl'Ognon, France) is identical to that used in previous studies [20][21][22] and consists of 256 elements, each 7 mm in diameter. The elements are distributed randomly on a spherical surface shell with a radius of curvature of 130 mm and a diameter of 170 mm.…”

“…The goal of any treatment planning will be to achieve high peak intensity levels in the focal plane and low intensity levels in the plane of the ribs. We previously demonstrated that the therapeutic random phased array can be used to produce 3D images of intervening structures such as ribs [20,21]. The images produced can then be used for refocusing the HIFU energy in the presence of rib cage by selectively deactivating elements which are shadowed by the ribs, thus minimizing depositing acoustic energy on the ribs.…”

The Core of Medical Imaging: State of the Art and Perspectives on the Detectors

“…Going from 2D to 3D ultrasound imaging, a 2D matrix transducer is required, entailing fabrication and implementation problems [6]. This is the reason why 3D ultrasound imaging methods based on 2-D array probes are continuing to improve in terms of fabrication and processing [7,8], and synthetic aperture ultrasound imaging [9,10]. Recently, the combination of miniaturized phased-array transducers and minimally invasive robotic surgery instruments is a further challenge in array development; preliminary phantom measurements demonstrate the feasibility to provide intraoperative image guidance and tissue characterization during endoscopic procedures [11].…”

Design of Ultrasonic Synthetic Aperture Imaging Systems Based on a Non-Grid 2D Sparse Array

“…Non-grid arrays (e.g., spiral or circular distributions), due to their good performance, are becoming very popular [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Recently, in [ 23 ], synthetic aperture imaging techniques were developed and experimentally tested for a random array. However, the irregular geometry of non-grid arrays makes redundancy identification a complex issue, and there is a lack of adequate tools to study how redundancy is organized on them and how it can be used to improve the imaging system design, and our contribution fills this gap in this important research and practical application area.…”