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.
Highlights
Phase contrast velocimetry cardiovascular magnetic resonance (PC-CMR) is a powerful and versatile tool allowing assessment of in vivo motion of the myocardium
We aim to demonstrate the feasibility of PC-CMR for accurately describing both myocardial motion and deformation in rodents by deriving global parameters such as peak velocities and maximum circumferential strain, as well as describing the spatial variability in essential parameters with higher resolution than have been previously reported
Validation of strain calculations In order to validate the PC-CMR-derived circumferential strain, the global Circumferential strain (Sc) was compared to echocardiographyderived global Sc
Summary
Phase contrast velocimetry cardiovascular magnetic resonance (PC-CMR) is a powerful and versatile tool allowing assessment of in vivo motion of the myocardium. Different techniques for the evaluation of myocardial function are available, including myocardial tagging [1], strain-encoded CMR (SENC) [2], displacement-encoded imaging with stimulated echoes (DENSE) [3] and phase contrast imaging (PC-CMR) [4]. The latter two offer pixel-wise measurement of displacement and velocity, respectively, allowing for high-resolution evaluation of tissue function. To accurately investigate the regional function e.g. in hearts with infarctions with various sizes, and in order to derive parameters such as subtle dyssynchrony, transmural functional gradients or longitudinal spread of dysfunction, data with higher spatial and temporal resolution along with appropriate post-processing procedures are essential
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