Left Ventricular Chamber Shape During Vena Caval Occlusion: Improved MRI-based Measurement of the End-Systolic Pressure-Volume Relationship in Normal Sheep

Abstract

The left ventricular (LV) end-systolic (ES) pressure volume relationship (ESPVR) is the cornerstone of systolic LV function analysis. We describe a 2D real-time (RT) MRI-based method (RTPVR) with separate software tools for 1) semi-automatic level set segmentation (LSSM) of the LV, 2) generation of synchronized pressure area loops and 3) calculation of the ESPVR. We used the RTPVR method to measure ventricular geometry, ESPAR and ESPVR during vena cava occlusion (VCO) in normal sheep. 10 adult sheep were anesthetized and 2D cross sectional RTMRI performed at apex, midventricle and base levels during separate VCOs. The Dice similarity coefficient was used to compare LSSM and manual image segmentation and thus determine LSSM accuracy. LV crosssectional area, major and minor axis length, axis ratio, major axis orientation angle and ESPAR were measured at each LV level. ESPVR was calculated with a modified Simpson's rule method. The Dice similarity coefficient between LSSM compared and manual segmentation by two readers was 87.31±2.51% and 88.13±3.43% respectively. All cross sections became more elliptical during VCO. The major axis orientation shifted during VCO but remained in the septo-lateral direction. LV chamber obliteration at the apical level occurred during VCO in 7 of 10 sheep. ESPAR was non-linear at all levels. Finally, ESPVR was non-linear because of apical collapse.LSSM segmentation of 2D RT MRI images is accurate and allows calculation of LV geometry, ESPAR and ESPVR during VCO. In the future, RTPVR will facilitate determination of regional systolic material parameters underlying ESPVR. End-systolic Pressure Volume Relationship by Real-time MRI 3 Word Count: 245 words End-systolic Pressure Volume Relationship by Real-time MRI