Normal Values of Magnetic Resonance T_1ρ Relaxation Times in the Adult Heart at 1.5 T MRI

Background: T_1ρ mapping is a new quantitative MRI technique in recent years. In order to use T_1ρ mapping as a noncontrast method to assess myocardial fibrosis, it is necessary to establish a range of normal values. Purpose: To establish a potential normal range of cardiac T_1ρ values in healthy adults and to explore the influence of slice location and gender on T_1ρ values. Study Type: Prospective. Population: A total of 57 healthy volunteers without cardiovascular risk factors (age 26.7 ± 11.8 years; 29 males). Field Strength/Sequence: 1.5 T; modified Look-Locker inversion recovery (MOLLI) (T₁ mapping), multiecho gradient-spin-echo (GraSE) (T₂ mapping) and T_1ρ-prepared steady-state free precession (T_1ρ mapping) sequences. Assessment: Basal, mid, and apical short-axis left ventricular T₁, T₂, and T_1ρ maps were acquired. T_1ρ maps at spin-locking frequencies of 5 and 400 Hz were subtracted to create myocardial fibrosis index (mFI) maps. Slice-average and global average T₁, T₂, T_1ρ, and mFI values were determined. Statistical Tests: Shapiro–Wilk test, Independent t-test, ANOVA test, Pearson correlation coefficient (r). Significance: P value < 0.05. Results: The global average values of T₁, T₂, T_1ρ, and mFI were 1053 ± 34 msec, 51.9 ± 2.3 msec, 47.9 ± 2.8 msec, and 4.4 ± 1.6 msec. T_1ρ values showed a significant gradual increase from the basal slice to the apical slice of the heart (basal 46.5 ± 2.7 msec, mid 48.0 ± 2.9 msec, apical 49.2 ± 3.3 msec). The T_1ρ and mFI values of females (49.7 ± 2.4 msec and 5.1 ± 1.2 msec, respectively) were significantly higher than those of males (46.2 ± 1.9 msec and 3.7 ± 1.7 msec, respectively). In addition, there was a moderate positive correlation between global T_1ρ values and global T₁ values (r = 0.44, P < 0.05) and a moderate positive correlation between global T_1ρ values and global T₂ values (r = 0.42, P < 0.05). Data Conclusion: In this study, the global T_1ρ values of healthy adults' hearts were 47.9 ± 2.8 msec. This study found that gender and slice location of myocardium can affect the T_1ρ values. Evidence Level: 4. Technical Efficacy: Stage 1.