Regional Evaluation of Left Ventricular Cardiac Diffusion Tensor Imaging Metrics in Healthy Subjects (RF_FR_352)

Cardiac Diffusion tensor imaging (cDTI) is an MRI technique to probe myocardial microstructure with clinical utility in characterizing and monitoring cardiomyopathies¹. As cDTI acquisitions continue to advance, it is necessary to establish healthy baseline values of key cDTI metrics like mean diffusivity (MD), fractional anisotropy (FA), and helix angle (HA). Previous studies assessed average global or whole-slice cDTI metrics from only a few slices (three to five) using stimulated-echo (STEAM) and spin-echo sequences^2,3. We hypothesize that there are no regional differences in cDTI metrics in a cohort of healthy adult volunteers.
 


Methods:

Forty (N=40) healthy volunteers (IRB approved, consented) underwent cardiac 3T MRI (Vida Fit, Siemens) with an 18-channel body coil and 32-channel spine coil. A free-breathing, M₁+M₂ compensated, slice-following, single-shot, spin-echo echo-planar imaging⁴ acquisition was used to acquire cDTI data with the following parameters: resolution=2×2×8mm³, FOV=256×256, GRAPPA=2, TE/TR=91ms/3R-R intervals, diffusion directions=15, b=350s/mm² and one b=0s/mm², averages=10 (5 blip-up+5 blip-down), full LV-coverage (N_slices=6-9), ~2 minutes and 40 seconds per slice. Volunteers were divided into four groups: (1) Male < 40 years old (yo), (2) Female < 40yo, (3) Male ≥40yo, and (4) Female ≥40yo (Table 1A).

Images were post-processed with CarDpy toolbox and distortion corrected^5,6. LV-segmentations and right-ventricular (RV) insertion points were manually identified to obtain regional masks according to the AHA 16-segment model⁷. MD, FA, and helix angle pitch (HAP) maps were generated.

We statistically compared global (all measures) versus regional (AHA regions), and group-wide (all subjects) versus group-specific (4 groups) in the following ways:

• Global group-specific median cDTI metrics to the global group-wide median.


• Regional group-wide median cDTI metrics to the global group-wide median.


• Regional group-specific median cDTI metrics to the global group-specific median.

For (1) normally distributed data underwent ANOVA and post-hoc pairwise Tukey's range testing. Non-normal distributions underwent Kruskal-Wallis testing and post-hoc Dunn’s testing. (2) and (3) were Bonferroni corrected. p < 0.05 was significant.

Results:

Significant differences were observed in BMI between females < 40yo and the other groups and in heart mass between males and females. Adequate image quality was observed in all slices (Fig-2).

For each comparison we found: (1) Group-specific global cDTI metrics were not significantly different from the group-wide global median (Table-1B). (2) Fig. 3A highlights regional group-wide differences for which only Segment-5 (basal inferolateral) was different for all metrics. (3) Fig. 3B highlights regional group-specific differences.

 

Conclusion:

Global cDTI metrics were consistent across groups. Regional differences observed may be attributed to physiological or imaging (e.g. off-resonance) effects. For the given cDTI protocol, this healthy adult cohort provides baseline cDTI metrics that can be used to evaluate changes observed in patients with cardiovascular disease. {

Funding: AHA.23PRE1018442, R01 HL152256, NSF 2205103, and NSF 2205043}