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Precision and reproducibility of T2 quantifications in myocardial T2 mapping: impact of the number of echoes and reconstruction model

Background

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.

Methods

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.

Results

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).

Figure 1
figure1

a) Numerical simulation results for the effect of number of echo images on the precision of the quantifications for different signal-to-noise ratios. As the number of echoes increases, the precision gets better till it nearly saturates for number of echoes ≥ 10. b) Accuracy, precision and reproducibility of T2 mapping when using different number of echo images. With increasing the number of echoes, estimated T2 values changes significantly when using 2-pt fits, while it shows consistency when using the 3-pt fits regardless of the number of echoes used for the estimation. Both precision and reproducibility increases when using more echo images for the T2 estimation. However, and similar to what numerical simulations predicts, the effect nearly saturates for number of echoes ≥ 10.

Figure 2
figure2

An example for the T2 maps of one healthy subject. The bull's-eyes shows the overall precision and reproducibility among the 10 subject in a segment-based analysis, when using the 3 echoes with 2-pt fit, and 10 echoes with 3-pt fit.

Conclusions

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.

Funding

N/A.

References

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Correspondence to Tamer Basha.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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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, W9 (2015). https://doi.org/10.1186/1532-429X-17-S1-W9

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Keywords

  • Myocardial Inflammation
  • Spin Relaxation
  • Conventional Sequence
  • Acquisition Window
  • Block Equation