Reproducibility of three different cardiac T -mapping sequences at 1.5T.

PURPOSE

To elucidate the impact of technical and intraindividual reproducibility on the overall variability of myocardial T relaxation times.

MATERIALS AND METHODS

Thirty healthy volunteers were examined three times (day 1 morning/evening, evening after 2-3 weeks) at 1.5T. During each examination three different T -mapping sequences were acquired twice at three slices in short axis view: multi-echo-spin-echo (MESE), T -prepared balanced steady-state free precession (SSFP) (T prep), and gradient-spin-echo with and without fat saturation (GraSE/GraSE ). Repeated measurements were performed for T prep and GraSE. Segmented T -maps were generated for each slice according to the American Heart Association (AHA) 16-segment model.

RESULTS

The coefficients of variation and intraclass correlation coefficients for intraobserver variability were: 1.3% and 0.89 for T prep, 1.5% and 0.93 for GraSE, 3.1% and 0.83 for MESE; and for interobserver variability: 3.3% and 0.66 for T prep, 2.0% and 0.83 for GraSE, 3.6% and 0.77 for MESE. No systematic difference of T times was observed due to diurnal effects and on long-term analysis using one-way analysis of variance (ANOVA) with Tukey-type multiple comparisons (morning vs. evening scan for T prep: 52.5 ± 2.4 vs. 51.7 ± 2.7 msec, P = 0.119; for GraSE: 58.6 ± 4.0 vs. 58.5 ± 3.8 msec, P = 0.984; for GraSE 57.1 ± 3.2 vs. 57.2 ± 3.9 msec, P = 0.998, and for MESE: 53.8 ± 2.7 vs. 53.3 ± 3.3 msec, P = 0.541; scans between weeks for T prep: 51.7 ± 2.7 vs. 51.4 ± 2.4 msec, P = 0.873; for GraSE: 58.5 ± 3.8 vs. 58.1 ± 3.4 msec, P = 0.736; for GraSE : 57.2 ± 3.9 vs. 57.0 ± 4.6 msec, P = 0.964, and for MESE: 53.3 ± 3.3 vs. 53.4 ± 2.4 msec, P = 0.970). ANOVA components, however, demonstrated a greater variance of T times over multiple timepoints than for repeated measurements within the same scan (variance components of the model fit for intraday variance vs. repeated measurements: T prep 2.22 vs. 1.36, GraSE 3.76 vs. 2.09, GraSE 3.96 vs. 1.58, MESE 1.86; and for interweeks variance vs. repeated measurements: T prep 2.21 vs. 0.80, GraSE 3.20 vs. 2.10, GraSE 8.82 vs. 1.18, and MESE 4.49).

CONCLUSION

Technical reproducibility and intra- and interobserver agreement of myocardial T relaxation times are excellent and intraindividual variation over time is small. Therefore, we consider subject-related factors to explain most of the interindividual variability of myocardial T times reported in previous studies. The acknowledgment of this subject-related, biological variability may be important for the future diagnostic value of T -mapping. J. Magn. Reson. Imaging 2016;44:1168-1178.