Vibro-acoustography beam formation with reconfigurable arrays

Abstract

In this work, we present a numerical study of the use of reconfigurable arrays (RCA) for vibro-acoustography (VA) beam formation. A parametric study of the aperture selection, number of channels, number of elements, focal distance, and steering parameters is presented in order to show the feasibility and evaluate the performance of VA imaging based on RCA. The transducer aperture was based on two concentric arrays driven by two continuous-wave or toneburst signals at slightly different frequencies. The mathematical model considers a homogeneous, isotropic, inviscid medium. The point-spread function of the system is calculated based on angular spectrum methods using the Fresnel approximation for rectangular sources. Simulations considering arrays with 50 × 50 to 200 × 200 elements with number of channels varying in the range of 32 to 128 are evaluated to identify the best configuration for VA. Advantages of two dimensional and RCA arrays and aspects related to clinical importance of the RCA implementation in VA such as spatial resolution, image frame-rate, and commercial machine implementation are discussed. It is concluded that RCA transducers can produce spatial resolution similar to confocal transducers, steering is possible in elevation and azimuthal planes, and optimal settings for number of elements, number of channels, maximum steering, and focal distance are suggested for VA clinical application. Furthermore, an optimization for beam steering based on the channel assignment is proposed for balancing the contribution of the two waves in the steered focus.

A beamforming study for implementation of vibro-acoustography with a 1.75-D array transducer

“…We have recently reported a simulation study of VA beamforming using a 2D reconfigurable array with elements of size 0.2 × 0.2 mm [22]. This type of transducer had elements that were small enough to greatly minimize the effects of grating lobes and would be able to focus and steer beams both in the azimuthal and elevational directions.…”

“…To achieve the same aperture size in the elevation direction (10.8 mm) while using square elements that have dimension λ/2, then assuming a frequency of 8 MHz we would need 113 elements on each side of the aperture. For the full 10.8 × 10.8 mm aperture currently considered it would require 12769 elements, which is far too many for current beamformers outside of using a reconfigurable array like that studied by Kamimura et al [22]. If a lower frequency that is within the bandwidth of the transducer is considered such as 5 MHz, it would still require a total of 5041 elements (71 × 71 elements) at λ/2 spacing (0.154 mm), which is still too large a number for individually addressing each element.…”

“…In a 2D array transducer, elevation focusing capabilities are similar to that in the azimuthal direction ( x -direction) and full electronic apodization, steering, and focusing are possible. A recent simulation study of the VA beam formation using a 2D reconfigurable array has been reported [22]. …”

Feasibility of vibro‐acoustography with a quasi‐2D ultrasound array transducer for detection and localizing of permanent prostate brachytherapy seeds: A pilot ex vivo study

“…A simulation study of VA using a 2D reconfigurable array has been previously reported by our research group. 37 While a 2D reconfigurable array is potentially an ideal solution for clinical implementation of VA, we have recently developed a VA system using a Q2D (in technical term, it is called 1.75D array transducer) array transducer as an intermediate step toward a desired 2D VA system. 36,38 This Q2D array US transducer has multiple rows of elements in elevation which can be electronically configured to optimally generate a close-to-symmetric ARF.…”

Vibroacoustography for the assessment of total hip arthroplasty

“…The feasibility of VA has been demonstrated for evaluating soft tissues, such as arteries (12,13), breast tissue (14,15), and prostate tissue (16). However, the implementation of VA in a commercial machine (17) and the development of new technologies for VA beam forming (18) open a new range of clinical applications.…”