The magnetic resonance Diffusion Tensor Imaging (DTI) is a powerful extension of Diffusion Weighted Imaging (DWI) utilizing multiple bipolar gradients, allowing for the evaluation of the microstructural environment of the highly anisotropic tissues. DTI was predominantly used for the assessment of the central nervous system (CNS), but with the advancement in magnetic resonance (MR) hardware and software, it has now become possible to image the peripheral nerves which were difficult to evaluate previously because of their small caliber. This study focuses on the assessment of the human median peripheral nerve ex vivo by DTI microscopy at 9.4 T magnetic field which allowed the evaluation of diffusion eigenvalues, the mean diffusivity and the fractional anisotropy at 35 μm in-plane resolution. The resolution was sufficient for clear depiction of all nerve anatomical structures and therefore further image analysis allowed the obtaining of average values for DT parameters in nerve fascicles (intrafascicular region and perineurium) as well as in the surrounding epineurium. The results confirmed the highest fractional anisotropy of 0.33 and principal diffusion eigenvalue of 1.0 × 10⁻⁹ m²/s in the intrafascicular region, somewhat lower values of 0.27 and 0.95 × 10⁻⁹ m²/s in the perineurium region and close to isotropic with very slow diffusion (0.15 and 0.05 × 10⁻⁹ m²/s) in the epineurium region.

Background: Mechanical work is traditionally defined by the pressure–volume loop, but its invasive nature limits routine clinical use. The myocardial work index (MWI) has emerged as a non-invasive alternative, combining strain and estimated pressure to assess cardiac performance. However, MWI does not account for ventricular geometry and treats the ventricle as a dimensionless chamber. According to Laplace’s law, wall stress and the true myocardial load depend on both pressure and ventricular geometry. Therefore, this study aims to develop and evaluate a geometry-informed myocardial work framework that provides a more physiologically representative estimate of mechanical energy expenditure. Method: In this proof-of-concept study, mechanical work was calculated using the one-fiber model of the left ventricle (LV) with Laplace-based geometric correction, integrating fiber stress over strain to derive the tension-adjusted myocardial work (TAMW) model. Strain was obtained from speckle tracking echocardiography along with pressure data while LV volumes and wall geometry were obtained from cardiac MRI. Two acute myocarditis patients with compact and dilated ventricles were analyzed, comparing cumulative and instantaneous work between MWI and TAMW. Performance gaps were quantified as the percentage difference in peak cumulative work. Results: Conventional MWI differed substantially between two cases (2576 vs. 1795 mmHg%, performance gap: 33.3%) whereas TAMW reduced this discrepancy to 7.5% (10,806 vs. 9789 mmHg%). TAMW also highlighted differences in temporal distribution of instantaneous work relative to MWI, reflecting the influence of ventricular geometry on contraction dynamics. Conclusions: TAMW incorporates the influence of geometry in the myocardial work framework revealing a more physiologically consistent reflection of myocardial effort across different ventricular geometries.

Background: Acute myocarditis (AM) affects myocardial structure and function, assessed by cardiac magnetic resonance late gadolinium enhancement (CMR-LGE) and speckle tracking echocardiography (STE), respectively; however, the correlation between the two techniques at the segmental level is inconsistent. We studied natural heterogeneity and anatomical orientation mismatch as potential causes of correlation discrepancy. Methods: A total of 30 AM patients underwent left ventricle LGE-CMR and STE measurement, acquiring 18 segmental values depicting edema extent and peak longitudinal strain, respectively. Baseline segmental correlation was compared to average patient segmental correlation and to segmental correlation after spatial resolution reduction achieved by averaging adjacent segments in four successive iterations, where the degree of spatial resolution reduction was evaluated based on the relative decrease in segmental standard deviation. Results: Baseline segmental correlation was weak, i.e., r = 0.24 (p < 0.05) but improved in fitted SLGE and SpLS baseline correlation (r₀ = 0.44, p < 0.05) and in average patient correlation (r = 0.55, p < 0.05). Iterative spatial resolution reduction increased the correlation to r₁ = 0.49 and r₂ = 0.51 and then decreased it to r₃ = 0.11 (p < 0.05) and r₄ = 0.07 (p > 0.05), with corresponding decreases in segmental standard deviation relative to baseline from σ₀ = 12.87 to σ/σ₀ = 0.68, 0.51, 0.38, and 0.29 in SLGE values and σ₀ = 4.77 to σ/σ₀ = 0.57, 0.41, 0.31, and 0.23 in SpLS. Conclusions: Improved correlation in average patients is associated with natural heterogeneity, which indicates a need to develop more robust indicators of ventricular function. The improved correlation in moderate spatial resolution reduction indicates a potential solution for anatomic orientation mismatch between CMR-LGE and STE techniques.