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.

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Radiofrequency ablation (RFA) is used to locally disrupt electrical propagation in myocardium and treat arrhythmias, and direct visualization of ablation lesions by acoustic radiation force methods may benefit RFA procedures. This work compares four imaging modalities, B-Mode, ARFI, STL-SWEI and MTL-SWEI, in their ability to resolve RFA lesions in four ex vivo experiments. Ablation lesions are shown to be marked by at least a local halving of ARFI displacements and doubling of shear wave speeds. In a controlled ablation of ex vivo porcine and canine cardiac tissue, STL-SWEI and ARFI are shown to have similar CNR, better than MTL-SWEI and B-Mode. The SWEI modalities are demonstrated to have improved imaging of distal lesion boundaries. Gaps smaller than 5 mm are visualized in ablation lines made of discretely-spaced ablations, and complex structures are reconstructed through depth in an “x” ablation experiment. Scans of suspended atria show increased noise, but successfully visualize ablations in ARFI, MTL-SWEI and STL-SWEI.

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In Part I of this paper, we detected elements blocked by ribs during simulated and in vivo transcostal liver scans, and we turned those elements OFF to compensate for the loss in visibility of liver vasculature. Here, we apply blocked-element detection and adaptive compensation to large synthetic-aperture (SA) data collected through rib samples ex vivo, in order to reduce near-field clutter and to recover lateral resolution. To construct large synthetic transmit and receive apertures, we collected the individual-channel signals from a fully sampled matrix array at multiple and known array locations across the tissue samples. The blocked elements in SAs were detected using the method presented in Part I and retroactively turned OFF, while the subapertures covering intercostal spaces were either compounded, or coherently summed using uniform and adaptive element-weighting schemes. Turning OFF the blocked elements reduced the reverberation clutter by 5 dB on average. Adaptive weighing of the nonblocked elements to rescale the attenuated spatial frequencies reduced sidelobe levels by up to 5 dB for the transcostal acquisitions, and demonstrated a potential to restore lateral resolution to the nonblocked levels. In addition, the arrival-time surfaces were reconstructed to estimate the aberration from intercostal spaces and to offer further means to compensate for the loss of focus quality in transthoracic imaging.

Approved direct-acting antiviral (DAA) regimens against hepatitis C virus (HCV) can cure nearly all patients; however, socioeconomic disparities may impact access and outcome. This study assesses socioeconomic factors, differences in insurance coverage and the drug prior authorization process in HCV-infected patients managed in community practices partnered with a dedicated pharmacy team with expertise in liver disease. This Institutional Review Board-approved, ongoing study captures data on a cohort of 2480 patients from community practices. Patients had chronic hepatitis C and were treated with DAA regimens selected by their physician. The HCV Health Outcomes Centers Network provides comprehensive patient management including a dedicated pharmacy support team with expertise in the prior authorization process. In this cohort, 60.1% were male, 49% were Hispanic Whites (HW), 37% were Non-Hispanic Whites (NHW), and 14% were Black/African American (BAA). Eighty-seven percent of patients were treatment-naïve, 74% were infected with genotype 1 virus and 63% had advanced fibrosis/cirrhosis (F3/F4 = 68.2% HW, 65.6% BAA, 55.4% NHW). Forty percent of patients were on disability with the highest percentage in the BAA group and less than one-third were employed full time, regardless of race/ethnicity. Medicare covered 42% of BAA patients versus 32% of HW and NHW. The vast majority of HW (80%) and BAA (75%) had a median income below the median income of Texas residents. Additionally, 75% of HW and 71% of BAA had median income below the poverty level in Texas. Despite the above socioeconomic factors, 92% of all prior authorizations were approved upon first submission and patients received DAAs an average of 17 days from prescription. DAA therapy resulted in cure in 95.3% of patients (sustained virologic response = 94.8% HW, 94.0% BAA, 96.5% NHW). Despite having more advanced diseases and more negative socioeconomic factors, >94% of HW and BAA patients were cured. Continued patient education and communication with the healthcare team can lead to high adherence and > 94% HCV cure rates regardless of race/ethnicity or underlying socioeconomic factors in the community setting.

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