Image Improved Intravoxel Incoherent Motion MRI With Optimized Trigger Delays Based on Strain Curve Analysis to Evaluate Myocardial Microvascular Dysfunction of Exertional Heat Illness

Background Intravoxel incoherent motion (IVIM) MRI has not been widely used and its role in evaluating exertional heat illness (EHI)‐related myocardial involvement remains unknown. Purpose To investigate the feasibility of strain curve‐derived trigger delay (TD) IVIM‐MRI and its role in assessing myocardial diffusion and microvascular perfusion of EHI patients. Study Type Prospective. Subjects A total of 42 male EHI patients (median age: 21 years) and 22 age‐ and sex‐matched healthy controls (HC). Field Strength/Sequence A 3‐T, diffusion‐weighted spin‐echo echo‐planar‐imaging sequence. Assessment IVIM‐MRI was acquired by conventional TD method (group A) or strain curve‐based TD method (group B) in random order. IVIM image quality was evaluated on a 3‐point Likert scale (1, nondiagnostic; 2, moderate; 3, good). Technical success was defined as image quality score = 3. IVIM‐MRI‐derived parameters (pseudo diffusion in the capillaries [D*], perfusion fraction [f], and slow apparent diffusion coefficient [D]) were compared between EHI and HC. Statistical Tests Student's t ‐tests, chi‐square tests, one‐way analysis of variance, receiver operating characteristic (ROC) curve analysis, Pearson's correlation coefficient ( r ). The statistical significance level was set at P < 0.05. Results IVIM‐MRI image quality score (median [interquartile range]: 3 [2, 3] vs. 2 [1–3]) and technical success rate (61.9%[13/21] vs. 28.6%[6/21]) were significantly improved in group B. EHI patients showed significantly decreased D* (118.1 ± 23.3 × 10 −3 mm 2 /sec vs. 142.7 ± 42.6 × 10 −3 mm 2 /sec) and f values (0.42 ± 0.12 vs. 0.51 ± 0.11) and significantly higher D values (3.0 ± 0.9 × 10 −3 mm 2 /sec vs. 2.5 ± 0.6 × 10 −3 mm 2 /sec) compared to HC. Relative to D and D*, f showed the most robust efficacy for detecting EHI‐related myocardial injury with the highest area under the ROC curve (0.906: 95% confidence interval, 0.799, 0.967) and sensitivity of 88.5% and specificity of 85.6%. Conclusion The strain curve‐based TD method significantly improved image quality and technical success rate of IVIM‐MRI, and f value may be an effective biomarker to assess myocardial microcirculation abnormalities of EHI patients. Evidence Level 2. Technical Efficacy Stage 3.