10B-5 4D Elasticity Imaging of PVA LV Phantom Integrated with Pulsatile Circulation System Using 2D Phased Array

Abstract

Myocardial ischemia or infarction alters myocardial contractility. Strain and strain rate imaging may be able to detect and monitor changes in myocardial contractility as well as evaluate viability. A challenging issue with cardiac elasticity imaging is that heart motion is 3D and complex. Currently available 1D or 2D elasticity imaging techniques are limited by significant out-of-imaging plane motion. To test phase-sensitive 3D speckle tracking of complex cardiac motion, a phantom experiment was performed using a commercial 2D phased array to image a Polyvinyl alcohol (PVA) cryogel left ventricular (LV) phantom connected to a controlled pulsatile circulation system. An LV phantom was constructed using 8% PVA cryogel embedded with ultrasound scatterers (Enamel paint). The mechanical and acoustical characteristics of the phantom were controlled by freeze-thaw cycles to mimic tissue. The LV phantom was connected to a pulsatile pump in combination with a pressure meter. The pulsatile pump was set with a stroke volume of 15-40 ml, heart rate of 10-40 beats per minute, and systole/diastole ratio of 25%-50% to mimic cardiac pulsation. 3D RF data were acquired in real time using a commercial 2D phased array (sono7500, Philips). Each data volume covered 46 slices (1 degree/slice) in azimuth, 18 slices (1.25 degrees/slice) in elevation (zenith) and 13 cm in depth. The kernel size for speckle tracking was set to be about 2 speckle sizes (3-4 mm in each direction). Elasticity images using 2D and 3D speckle tracking on 4D data sets (3D in space with time) of the phantom were compared. 3D speckle tracking successfully estimated the displacement in the third dimension. In addition, 3D tracking corrected overestimates or underestimates in 2D due to out-of-plane motion, and azimuthal displacement in 3D tracking was smoother than 2D. 3D and 2D tracking of simulated data further support these results. Preliminary results demonstrate the feasibility of 4D elasticity imaging of complex cardiac motion.