Yoko Okamura

RSNA QIBA ultrasound shear wave speed Phase II phantom study in viscoelastic media

Using ultrasonic shear wave speed (SWS) estimates has become popular to noninvasively evaluate liver fibrosis, but significant inter-system variability in liver SWS measurements can preclude meaningful comparison of measurements performed with different systems. The RSNA Quantitative Imaging Biomarker Alliance (QIBA) ultrasound SWS committee has been developing elastic and viscoelastic (VE) phantoms to evaluate system dependencies of SWS estimates. The objective of this study is to compare SWS measurements between commercially-available systems using phantoms that have viscoelastic properties similar to those observed in normal and fibrotic liver. CIRS, Inc. fabricated three phantoms using a proprietary oil-water emulsion infused in a Zerdine® hydrogel that were matched in viscoelastic behavior to healthy and fibrotic human liver data. Phantoms were measured at academic, clinical, government and vendor sites using different systems with curvilinear arrays at multiple focal depths (3.0, 4.5 & 7.0 cm). The results of this study show that current-generation ultrasound SWS measurement systems are able to differentiate viscoelastic materials that span healthy to fibrotic liver. The deepest focal depth (7.0 cm) yielded the greatest inter-system variability for each phantom (maximum of 17.7%) as evaluated by IQR. Inter-system variability was consistent across all 3 phantoms and was not a function of stiffness. Median SWS estimates for the greatest outlier system for each phantom/focal depth combination ranged from 12.7-17.6%. Future efforts will include performing more robust statistical analyses of these data, comparing these phantom data trends with viscoelastic digital phantom data, providing vendors with study site data to refine their systems to have more consistent measurements, and integrating these data into the QIBA ultrasound shear wave speed measurement profile.

Microvascular blood flow in the thyroid: Preliminary results with a novel imaging technique

Nodules in the thyroid are present in 13-76 % of ultrasound (US) imaging evaluations; although only 4-15 % are malignant. A better understanding of thyroid nodule vascularity might be clinically helpful and the purpose of this study was thus to determine the flow imaging capabilities of a new prototype US image processing technique (SMI; Toshiba Medical Systems, Tokyo, Japan) for the depiction of microvascular flow in normal thyroid tissue and thyroid nodules compared to standard color and power Doppler imaging (CDI and PDI). SMI is a novel, microvascular flow imaging mode implemented on the Aplio 500 scanner (Toshiba). By analyzing clutter motion and using a new adaptive algorithm to identify and remove tissue motion SMI is designed to improve the visualization of microvascular blood flow. SMI depicts this information as a color overlay or as a monochrome map of flow. Ten healthy volunteers and 22 patients, with 25 thyroid nodules, were studied. Subjects underwent a thyroid US examination consisting of grayscale US, CDI and PDI followed by color and monochrome SMI. In the volunteers, pulsed Doppler guided by the 4 flow modes determined the lowest velocity measurable within the normal thyroid. For the patient data, 2 radiologists independently scored overall flow detection, vessel branching and noise on a visual analog scale of 1 (worst) to 10 (best). In the volunteers color and monochrome SMI captured microvasculature with lower velocities than CDI and PDI (2.2 ± 0.35 and 2.1 ± 0.32 cm/s vs. 2.6 ± 0.44 and 2.8 ± 0.77 cm/s; p <; 0.012). For all 25 nodules both readers found that color and monochrome SMI showed more microvascular flow and provided better depiction of the vessel branching compared to CDI and PDI (p <; 0.0001). Clutter noise was significantly higher in the monochrome SMI mode than in the other 3 modes (p <; 0.001). Consequently, initial results indicate that SMI can depict more detailed peri- and intra-nodular thyroid microvascular flow than CDI and PDI.