In Vivo acoustic radiation force impulse imaging of the cardiac cycle

In vivo ARFI images of an exposed canine heart were acquired through multiple cardiac cycles. The matched eletrocardiogram (ECG) was also recorded. Sequences with the radiation force pulse amplitude set to zero were also acquired to measure potential artifacts within the ARFI images. A radiofrequency ablation was performed on the pericardial surface of the left ventricular free wall, creating a lesion that did not vary in stiffness during a heartbeat though continued to move physiologically with the rest of the heart. The ARFI images showed a semispherical, stiffer region at the ablation site that displaced and varied less throughout entire cardiac cycle. When registered with the ECG, the changing displacements within the sequence of ARFI images reflect the expected stiffness changes of the myocardium during the entire cardiac cycle. The results show great promise for realtime cardiac ARFI imaging.