Shear Wave Velocity Imaging Using Transient Electrode Perturbation: Phantom and ex vivo Validation

Abstract

This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures.

Scatterer Number Density Considerations in Reference Phantom-Based Attenuation Estimation

“…We noted that small differences in envelope SNR had a large effect on the attenuation estimation variance once the SNR began to significantly deviate from 1.91. Ex vivo porcine (Bush et al, 1993; Zhou et al, 2013), bovine (Bevan and Sherar, 2001a, 2001b; Dewall et al, 2010; Gertner et al, 1997; Luchies et al, 2012, 2012; Parker, 1983; Pereira and Maciel, 2001), rat (Kemmerer and Oelze, 2012), and human (Machado et al, 2006) liver have all been used for the development of ultrasonic tissue characterization algorithms based on features extracted from RF data. However, we are not aware of any studies comparing estimates of envelope statistics in excised liver with estimates of envelope statistics in an in vivo setting.…”

A comparison of model based and direct optimization based filtering algorithms for shearwave velocity reconstruction for electrode vibration elastography

“…Therefore, the full data set is assembled by vibrating the needle multiple times and recording data in synchronization at five lateral locations using narrow focussed beams. This provides a frame rate of around 2000 Hz [9]. A 128-element linear array transducer operating at 5 MHz center frequency, 4.5 cm imaging depth, 3 cm focal depth and each A-line sampled at 40 MHz is used for RF echo data acquisition.…”

Three-Dimensional Sheaf of Ultrasound Planes Reconstruction (SOUPR) of Ablated Volumes

“…It has potential to augment traditional B-scans and assist the clinician in delineating ablation boundaries more accurately. Unlike X-ray computed tomography (CT) or magnetic resonance imaging (MRI), traditional ultrasound elastography has been limited to single imaging planes, over which strain is estimated, and the Young's modulus (stiffness) is reconstructed by solving the inverse problem [6], [7], [8], [9]. Shear wave velocity (SWV) and shear modulus can also be estimated for these imaging planes [10].…”