WORKSHOP PRESENTATION Open Access Precision and reproducibility of T2 quantifications

Quantitative myocardial T2 is a promising technique to assess myocardial inflammation and edema (1). Recent implementations have utilized T2-prepared (T2prep) SSFP sequences to acquire a multiple T2 weighted images at different echo times, and generate T2 maps based on a 2-parameter (2P-fit) model of T2 decay (2,3). Recently, a 3-parameter fitting (3P-fit) model was found superior to the conventional 2P-fit model, as it compen-sates for T1 relaxation effect, and results in more accu-rate T2 measurements (4). In this work, we sought to characterize the 3P-fit approach in terms of precision and reproducibility and to evaluate the influence of the number of employed T2prep echo times on these two metrics. Methods Monte-Carlo simulations (1000 repetitions) were per-formed to study the effect of increasing the number of T2prep images. Block equation was used to simulate the signal intensities of a presumed tissue of T2 = 50ms at different T2prep echo times and different SNR levels. T2 was then estimated using a 2- and 3-parameter fitting model, and the precision was quantified for each model. Ten healthy subjects (27±10 y/o, 5m) were then imaged using a 1.5 T Phillips scanner with a free-breathing ECG-triggered single shot T2prep bSSFP sequence (FOV = 320×320 mm2, in-plane resolution = 2.5×2.5 mm2, slice thickness = 8mm, TR/TE = 2.2/1.1ms, FA = 40°, SENSE rate = 2, acquisition window = 140 ms, 14 T2prep echo times = 0,25,35,…135,145 ms). A 4s rest period after each image to allow for full spin relaxation. Data were reconstructed using the 3P-fit model. For comparison, a conventional T2 mapping sequence was acquired (Breath hold, 3 T2prep echo times = 20,50,75ms, and 2P-fit model). For each subject, both sequences were repeated 5 times. Precision and repro-ducibility were compared using different subset of T2prep echo times. Based on these results, an optimized T2 mapping sequence using 10 T2prep echoes and a 3P-fit model is proposed and evaluated in-vivo in 10 healthy subjects (29±17 y/o, 4m). This sequence is com-pared to the same conventional T2 mapping sequence in term of precision and reproducibility