Free-breathing multi-slice myocardial T2 mapping using slice-selective T2 magnetization preparation
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: W3 (2015)
Quantitative myocardial T2 mapping allows non-invasive assessment of myocardial inflammation/edema . Current implementations commonly use a T2-prepared (T2prep) SSFP sequence to acquire different T2 weighted images at different echo times to generate the T2 maps [2, 3]. However, all current techniques are designed for single slice acquisition with long rest cycles (3-6 sec) after each T2prep image acquisition to allow for full spin recovery. This markedly increases the overall scan time, especially if multiple slices are to be acquired in serial. In this study, we propose a novel multi-slice T2 mapping sequence, which uses slice-selective T2prep pulses combined with an interleaved slice acquisition scheme to provide a fast multi-slice T2 mapping.
Fig. 1 shows a schematic for the proposed sequence with the proposed slice selective T2prep pulses and the interleaved slice acquisition. Upon the acquisition of a specific slice, the other slices are selectively prepared, excited and acquired during the relaxation period of that slice. Thus, one T2prep image is acquired at every heartbeat. Prospective slice tracking and retrospective image registration were used to correct for respiratory motion. Phantom imaging was performed using NiCl2 doped agarose vials, whose T2/T1 values spanned the ranges of values found in the blood and myocardium. Ten healthy adults subjects (29±17 y, 4m) were imaged on a 1.5T Phillips scanner. A free-breathing single-shot ECG-triggered slice-selective T2prep bSSFP sequence with the following parameters was used for acquisition of five mid-ventricular short-axis slices, FOV=320×320 mm2, in-plane resolution=2.5×2.5mm2, slice thickness=8mm, slice gap=4mm, TR/TE=2.2/1.1ms, α=40°, SENSE rate=2, acquisition window=140 ms. For comparison, a conventional breath-hold single-slice T2prep bSSFP sequence was performed to image the middle of the 5-slices. All acquisitions were performed using the conventional 3-images with T2prep echo times = 0,25,50 ms (2), with a SAT image added to compensate for the T1 relaxation time during readout . T2 maps were then generated using the 3-parameter fitting model .
Fig. 2a shows the correlation between T2 measurements using the single and multi-slice sequences in phantom compared to spin echo. Figure 2b. shows an example T2 maps. Fig. 2c. shows a comparison between T2 maps generated using the single slice and multi slice sequences. The average scan time was 20 heartbeats for the 5 slices using the multi-slice and 13 heartbeats per slice using the single slice sequence. The average T2 across the myocardium and over all healthy subjects was 51ms and 48ms using the single and the multi-slice sequence respectively (p=0.1).
The proposed multi-slice T2 mapping pulse sequence allows myocardial T2 measurements over the entire left ventricle by imaging of 5 interleaved slices in 20 heartbeats.
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Basha, T., Roujol, S., Berg, S. et al. Free-breathing multi-slice myocardial T2 mapping using slice-selective T2 magnetization preparation. J Cardiovasc Magn Reson 17 (Suppl 1), W3 (2015). https://doi.org/10.1186/1532-429X-17-S1-W3