Factors impacting detection of untethered scatterers within viscoelastic background by ARFI Surveillance of Subcutaneous Hemorrhage (ASSH): In silico demonstration

ARFI Surveillance of Subcutaneous Hemorrhage (ASSH) is a method for noninvasively detecting and monitoring subcutaneous bleeding, in vivo. It has been implemented in relevant animal models and in patients undergoing percutaneous coronary catheterization to monitor hemorrhage at sites of vascular injury. In ASSH, regions of hemorrhage are identified by elevated variance in measured ARF-induced tissue acceleration profiles. However, it is well known that increased variance, or ℌjitterH, can be caused by a number of factors nonspecific for the presence of hemorrhage, such as low ultrasonic signal-to-noise ratio (SNR) or small tracking kernel size. To explore the sources of jitter in ASSH, a model of low-reflection-amplitude, untethered scatterers (mimicking red blood cells) within a viscoelastic medium under ARF excitation is developed using FEM simulation and Field II. ASSH profiles are generated with a range of system SNR levels, tracking kernel sizes, and untethered scatterer concentrations and displacement magnitudes. The optimal thresholds for detecting the untethered scatterers are determined using receiver operating characteristic (ROC) curve analysis. The results suggest that, given adequate system SNR (≤ 40 dB) and optimal threshold and kernel selection, ASSH can achieve high performance (≤ 0.9 area under the ROC curve) for detecting untethered scatterers.