Toward Standardized Acoustic Radiation Force (ARF)-Based Ultrasound Elasticity Measurements With Robotic Force Control

Abstract

Objective Acoustic radiation force (ARF)-based approaches to measure tissue elasticity require transmission of a focused high-energy acoustic pulse from a stationary ultrasound probe and ultrasound-based tracking of the resulting tissue displacements to obtain stiffness images or shear wave speed estimates. The method has established benefits in biomedical applications such as tumor detection and tissue fibrosis staging. One limitation, however, is the dependence on applied probe pressure, which is difficult to control manually and prohibits standardization of quantitative measurements. To overcome this limitation, we built a robot prototype that controls probe contact forces for shear wave speed quantification. Methods The robot was evaluated with controlled force increments applied to a tissue-mimicking phantom and in vivo abdominal tissue from three human volunteers. Results The root-mean-square error between the desired and measured forces was 0.07 N in the phantom and higher for the fatty layer of in vivo abdominal tissue. The mean shear wave speeds increased from 3.7 to 4.5 m/s in the phantom and 1.0 to 3.0 m/s in the in vivo fat for compressive forces ranging from 2.5 to 30 N. The standard deviation of shear wave speeds obtained with the robotic approach were low in most cases (< 0.2 m/s) and comparable to that obtained with a semiquantitative landmark-based method. Conclusion Results are promising for the introduction of robotic systems to control the applied probe pressure for ARF-based measurements of tissue elasticity. Significance This approach has potential benefits in longitudinal studies of disease progression, comparative studies between patients, and large-scale multidimensional elasticity imaging.

Effect of Open-Ended Coaxial Probe-to-Tissue Contact Pressure on Dielectric Measurements

“…We believe that applying different pressures changes the cellular matrix, which results in a different electromagnetic response. Moreover, the effect of pressure-dependent measurement responses is not limited to this specific domain, but similar trends are visible in other biology-related disciplines, as mentioned before [24][25][26][27][28].…”

“…Unfortunately, there is no guideline on when the operator should stop, i.e., which probe-to-tissue contact pressure is desired and how it varies over time. The literature reveals that the probe-to-tissue contact pressure in other biology-related disciplines has a significant impact on the measurements of, for instance, pressure waves in acoustic radiation force (ARF)-based ultrasound elasticity measurements [24], low-frequency electromagnetic waves for electrical bioimpedance measurements [25][26][27], and electromagnetic waves in the visible light and infrared spectrum for measurements of optical properties [28]. These results suggest that the probe-to-tissue contact pressure is significant and cannot be neglected.…”

Influence of Probe Pressure on Ultrasound-Based Shear Wave Elastography of the Liver Using Comb-Push 2-D Technology

“…In one study, morphometric changes caused by cirrhosis associated with all aetiologies commonly exhibited atrophy of the medial and anterior segments and right lobe and hypertrophy of the lateral segment and caudate lobe (Ozaki et al 2016). Finally, the standardization of maximum intercostal probe pressure with a robot force-controlled method (Bell et al 2016) would not improve reliability because the SCD differs in every patient, and different conditions of subcutaneous fat cause the ultrasound waves to attenuate differently (Mast et al 1999). Therefore, the SWE examination performed with an intercostal approach is highly dependent on a B-mode image of high quality (Dietrich et al 2017), which is very difficult to achieve with a robot.…”

“…Subsequently, discussions have arisen on the difficulties in standardizing how much probe pressure should be applied (Barr and Zhang 2012;Lam et al 2016). In studies that performed superficial tissue elasticity measurements, where a strain or ARFI approach was used, robot systems were employed to allow control of the pre-compressive force (Bell et al 2016). An experimental study on patients that received kidney transplants used ARFI and a mechanical device, which allowed control of the applied probe pressure (Syversveen et al 2012).…”

Evaluation of Control Strategies for a Tele-manipulated Robotic System for Remote Trauma Assessment

“…Another advance was made in [15], in which a learning-by-demonstrating control model was employed to teach a robot to perform an abbreviated eFAST scan, though without the use of force feedback. Extensive work on force-feedback control is present in [1,2] where a custom robot was developed to control the ultrasound probe contact forces during an ultrasound scan for tissue elasticity measurement. In [24], a haptic tele-manipulated system was developed for ultrasound, but with a severely limited workspace.…”