2-D Ultrasound Shear Wave Elastography With Multi-Sphere-Source External Mechanical Vibration: Preliminary Phantom Results.

Ultrasound shear wave elastography (SWE) imaging is emerging as a quantitative and non-invasive tissue characterization modality. Shear wave generation using external mechanical vibration (EMV) has received extensive research interest over acoustic radiation force impulse (ARFI) because of its low cost and potential for portability. In this paper, we propose an EMV concept with multiple spherical sources that can be easily reconfigured in three configurations to induce unique shear wave propagation patterns. We introduce two design embodiments of this concept bench test design for proof of concept and a clinically deployable design. The latter is designed to incorporate size, ergonomics, portability and power consumption considerations and constraints. Experimental validation on elasticity phantoms using both EMV designs demonstrates shear wave generation and elasticity reconstruction comparable in performance to ElastQ, a commercial ARFI-based shear elastography technology from Philips. In addition, the local displacement amplitude induced by EMV is 10 times greater than that induced by ARFI at the same given depth. Finally, the multiple configurations of the presented EMV design would allow exploration of advanced elastography methods such as tissue anisotropic elasticity.

Renal Volume Estimation Using Freehand Ultrasound Scans: An Ex Vivo Demonstration.

Renal volume has the potential to serve as a robust biomarker for tracking the onset and progression of renal diseases and also for quantifying renal function. We propose a method to estimate renal volumes using freehand ultrasound scans at the point of care. A conventional ultrasound probe was augmented with an Intel RealSense D435 i camera. Visual inertial simultaneous localization and mapping was used to localize the probe in free space. The acquired 2-D ultrasound images, segmented by trained clinicians, were combined with the estimated poses of the probe to yield accurate volumes. The method was tested on two ex vivo sheep kidneys embedded in gelatin phantoms. Four different scanning protocols were tested: transverse linear, transverse fan, longitudinal linear and longitudinal fan. The estimated renal volumes were compared with those obtained using the water displacement method, the ellipsoidal method and computed tomography imaging. The water displacement method yielded mean volumes of 66.00 and 66.20 mL for kidneys 1 and 2, respectively (ground truth). Freehand ultrasound scans produced mean volumes of 64.08 mL (2.90% error) and 65.25 mL (1.40% error); the ellipsoidal method yielded volumes of 57.49 mL (12.90% error) and 60.15 mL (9.13% error); and computed tomography yielded a volume of 63.00 mL (4.54% error).

Noninvasive In vivo assessment of renal tissue elasticity during graded renal ischemia using MR elastography.

OBJECTIVES: : Magnetic resonance elastography (MRE) allows noninvasive assessment of tissue stiffness in vivo. Renal arterial stenosis (RAS), a narrowing of the renal artery, promotes irreversible tissue fibrosis that threatens kidney viability and may elevate tissue stiffness. However, kidney stiffness may also be affected by hemodynamic factors. This study tested the hypothesis that renal blood flow (RBF) is an important determinant of renal stiffness as measured by MRE. MATERIAL AND METHODS: : In 6 anesthetized pigs MRE studies were performed to determine cortical and medullary elasticity during acute graded decreases in RBF (by 20%, 40%, 60%, 80%, and 100% of baseline) achieved by a vascular occluder. Three sham-operated swine served as time control. Additional pigs were studied with MRE 6 weeks after induction of chronic unilateral RAS (n = 6) or control (n = 3). Kidney fibrosis was subsequently evaluated histologically by trichrome staining. RESULTS: : During acute RAS the stenotic cortex stiffness decreased (from 7.4 ± 0.3 to 4.8 ± 0.6 kPa, P = 0.02 vs. baseline) as RBF decreased. Furthermore, in pigs with chronic RAS (80% ± 5.4% stenosis) in which RBF was decreased by 60% ± 14% compared with controls, cortical stiffness was not significantly different from normal (7.4 ± 0.3 vs. 7.6 ± 0.3 kPa, P = 0.3), despite histologic evidence of renal tissue fibrosis. CONCLUSION: : Hemodynamic variables modulate kidney stiffness measured by MRE and may mask the presence of fibrosis. These results suggest that kidney turgor should be considered during interpretation of elasticity assessments.