Precision and reproducibility of T2 quantifications in myocardial T2 mapping: impact of the number of echoes and reconstruction model
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: W9 (2015)
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 compensates for T1 relaxation effect, and results in more accurate 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.
Monte-Carlo simulations (1000 repetitions) were performed 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 reproducibility 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 compared to the same conventional T2 mapping sequence in term of precision and reproducibility.
T2 measurements using a 2P-fit model are dependent on the number of T2prep echo times (Figure 1). The 3P-fit model provides T2 measurements independent from the number of T2prep echo times. Higher precision and reproducibility was achieved with increased number of T2prep echo times. Improved in-vivo precision and reproducibility was achieved using the proposed sequence when compared to the conventional sequence (7ms vs. 11ms p=XX and 1.2ms vs. 2.4ms p=XX, respectively) (Figure 2).
The proposed sequence using 10 T2prep echo times and a 3P-fit model is independent from the number of T2prep echo times and provides better in-vivo precision and reproducibility than the conventional technique.
He : JMRI. 2006
Giri : MRM. 2012
Van Heeswijk : JACC. 2012
Akçakaya : MRM. 2014
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Basha, T., Akcakaya, M., Roujol, S. et al. Precision and reproducibility of T2 quantifications in myocardial T2 mapping: impact of the number of echoes and reconstruction model. J Cardiovasc Magn Reson 17 (Suppl 1), W9 (2015). https://doi.org/10.1186/1532-429X-17-S1-W9