Development and evaluation of pulse sequences for freehand ARFI imaging

Acoustic Radiation Force Impulse (ARFI) imaging techniques can be used to non-invasively evaluate the relative stiffness of tissue; potentially aiding in the identification of stiff cancerous lesions or vulnerable soft lipid filled plaques in vasculature. In this work, we developed several pulse sequences that implement conventional B-mode interleaved with ARFI imaging for various frame rates and scan durations (ranging from 20 fps for 1 sec to 1 fps for 90 seconds). On-axis displacement estimates were calculated using a GPU processor for faster computation times. The clinical feasibility of the proposed pulse sequences was evaluated on the basis of transducer face heating, ISPTA, MI, and the observed spatial and temporal consistency of images acquired in vivo. Transducer face heating was <;2°C and FDA acoustic exposure limits were not exceeded. In phantoms, image degradation during a freehand swept scan is shown to be dependent upon the sonographer. In vivo multi-frame movie sequences showed consistent measurements of on-axis displacements across multiple frames and acquisitions. Overall data acquisition, processing, and display frame rates of 1.0 Hz were achieved, allowing for low frame rate sequences to provide feedback information during the swept scan.