Novel insight into the detailed myocardial motion and deformation of the rodent heart using high-resolution phase contrast cardiovascular magnetic resonance

Abstract

BackgroundPhase contrast velocimetry cardiovascular magnetic resonance (PC-CMR) is a powerful and versatile tool allowing assessment of in vivo motion of the myocardium. However, PC-CMR is sensitive to motion related artifacts causing errors that are geometrically systematic, rendering regional analysis of myocardial function challenging. The objective of this study was to establish an optimized PC-CMR method able to provide novel insight in the complex regional motion and strain of the rodent myocardium, and provide a proof-of-concept in normal and diseased rat hearts with higher temporal and spatial resolution than previously reported.MethodsA PC-CMR protocol optimized for assessing the motion and deformation of the myocardium in rats with high spatiotemporal resolution was established, and ten animals with different degree of cardiac dysfunction underwent examination and served as proof-of-concept. Global and regional myocardial velocities and circumferential strain were calculated, and the results were compared to five control animals. Furthermore, the global strain measurements were validated against speckle-tracking echocardiography, and inter- and intrastudy variability of the protocol were evaluated.ResultsThe presented method allows assessment of regional myocardial function in rats with high level of detail; temporal resolution was 3.2 ms, and analysis was done using 32 circumferential segments. In the dysfunctional hearts, global and regional function were distinctly altered, including reduced global peak values, increased regional heterogeneity and increased index of dyssynchrony. Strain derived from the PC-CMR data was in excellent agreement with echocardiography (r = 0.95, p < 0.001; limits-of-agreement −0.02 ± 3.92%strain), and intra- and interstudy variability were low for both velocity and strain (limits-of-agreement, radial motion: 0.01 ± 0.32 cm/s and −0.06 ± 0.75 cm/s; circumferential strain: -0.16 ± 0.89%strain and −0.71 ± 1.67%strain, for intra- and interstudy, respectively).ConclusionWe demonstrate, for the first time, that PC-CMR enables high-resolution evaluation of in vivo circumferential strain in addition to myocardial motion of the rat heart. In combination with the superior geometric robustness of CMR, this ultimately provides a tool for longitudinal studies of regional function in rodents with high level of detail.

Assessment of Regional Myocardial Work in Rats

“…strain 8 of the myocardium with high spatiotemporal resolution. No studies have evaluated in vivo regional work in small animal hearts.…”

“…8 All MRI acquisitions were respiration-gated and prospectively triggered at the peak of the R-wave. Anesthesia was induced using a mixture of O 2 and 4.0% isoflurane and maintained using O 2 and 1.5% to 3.0% isoflurane, in freely breathing animals.…”

“…8,10 Three short-axis slices were planned 11 : basal, mid-ventricular, and apical (+3, 0, and −3 mm from the longitudinal midpoint of the ventricle), also covering >100% of the R-R interval. PC-MRI imaging parameters were TE=2.22 to 2.26 ms; TR=2.93 to 3.21 ms; field-ofview=50×50 mm; matrix 128×128; slice thickness 1.5 mm; flip angle 7°; venc=13.9 cm/s.…”

“…PC-MRI imaging parameters were TE=2.22 to 2.26 ms; TR=2.93 to 3.21 ms; field-ofview=50×50 mm; matrix 128×128; slice thickness 1.5 mm; flip angle 7°; venc=13.9 cm/s. Acquisition time for a complete PC-MRI slice (with 2× signal averaging using rotating field-of-view 8 ) was 15 to 20 minutes.…”

“…8 All operator inputs, including MR imaging segmentation, were done under identical brightness and contrast settings to ensure consistency between subjects. Each of the 3 slices was divided into 32 sectors 6 in which regional circumferential strain was calculated as previously described.…”