Right ventricular strain imaging using 3D SPAMM combined with optical flow tracking

Abstract

Summary A SPAMM sequence and optical flow tracking method that permits evaluation of strain in all 3 dimensions simultaneously in a single acquisition was successfully applied to the right ventricle. Background Presently there is no method of evaluating right ventricle function that simultaneously accounts for its complex geometry and motion. RV strain imaging is promising for evaluating regional dysfunction but to date it has not been possible to assess all 3 dimensions in a single acquisition. A novel variant of SPAMM tagging combined with optical flow tracking is available at our institution that can evaluate strain and torsion simultaneously in all 3 dimensions. We have applied this method to the right ventricle. Methods Data was analyzed, with attention to the right ventricle, from data acquired during a study of left ventricular remodeling post acute infarction. Imaging was obtained using respiratory triggering, with animals ventilated under general anesthesia, and triggering from invasive monitoring of left-sided pressures. 3-D tagging was performed at early (less than one week) and later (4-6 week) postoperative time points. Typical parameters for the 3-D tagging sequence at high resolution are: slice thickness 1mmx0.5mmx2mm interpolated to 0.5x0.5x2mm; 4mm tag spacing; coverage of about half of the heart, at mid-ventricle level; 6 nex; 30 minute acquisition time with respiratory gating. 5 or 6 phases were acquired during average systole. Typical parameters for the sheep 3-D tagging sequence at low resolution are: slice thickness 2mmx1mmx2mm interpolated to 1x1x2 ; whole heart coverage; 6mm tag spacing; 4 nex (4 signal acquisitions); 45 minute acquisition time with respiratory gating. Tag tracking was performed using an optical flow method and principal strain was calculated from the displacement using a custom program.