10C-4 Improved Myocardial Motion Tracking in Mouse Echocardiography Using Large-Diameter Microbubbles

High frequency (25-35 MHz), transthoracic, adult mouse echocardiography images sometimes exhibit low echogenecity in segments of the myocardium, resulting in degraded regional motion tracking. In this work, we performed high frequency (30 MHz) transthoracic ultrasound scanning on the left ventricle (LV) of normal C57BL/6 mice. Large-diameter microbubbles (range=2-8 mum, median~=5 mum) were used to enhance myocardial image signal via microbubbles lodging in the myocardial capillary bed [1]. Microbubbles produced an image intensity enhancement of 5-10 dB throughout the myocardium - especially in known signal dropout susceptible locations such as the septal wall. The motion analysis was performed using various filtering and tracking block size parameters, and the results were compared between analysis on microbubble-enhanced images and control echocardiographic images where no microbubbles were employed. The use of microbubbles allowed motion tracking without image pre-filtering and thus reduced the smoothing effect on motion tracking that filtering can cause. Motion tracking using smaller tracking block size (0.2 x 0.2 mm
²
vs. 0.4 x 0.4 mm
²
) on microbubble- enhanced images yielded finer tracking accuracy and better resolution than when tracking was performed on control images. Microbubble enhancement also facilitated motion tracking measurements using "real-time" image sequences (requiring an acquisition lasting a few seconds) versus the previously preferred EKV data acquisition method (i.e., an ECG-gated EKV acquisition mode) that required 2-3 minutes.