Abstract
PurposeTo enable free‐breathing whole‐heart 3D T2 mapping with high isotropic resolution in a clinically feasible and predictable scan time. This 3D motion‐corrected undersampled signal matched (MUST) T2 map is achieved by combining an undersampled motion‐compensated T2‐prepared Cartesian acquisition with a high‐order patch‐based reconstruction.MethodsThe 3D MUST‐T2 mapping acquisition consists of an electrocardiogram‐triggered, T2‐prepared, balanced SSFP sequence with nonselective saturation pulses. Three undersampled T2‐weighted volumes are acquired using a 3D Cartesian variable‐density sampling with increasing T2 preparation times. A 2D image‐based navigator is used to correct for respiratory motion of the heart and allow 100% scan efficiency. Multicontrast high‐dimensionality undersampled patch‐based reconstruction is used in concert with dictionary matching to generate 3D T2 maps. The proposed framework was evaluated in simulations, phantom experiments, and in vivo (10 healthy subjects, 2 patients) with 1.5‐mm3 isotropic resolution. Three‐dimensional MUST‐T2 was compared against standard multi‐echo spin‐echo sequence (phantom) and conventional breath‐held single‐shot 2D SSFP T2 mapping (in vivo).ResultsThree‐dimensional MUST‐T2 showed high accuracy in phantom experiments (R2 > 0.99). The precision of T2 values was similar for 3D MUST‐T2 and 2D balanced SSFP T2 mapping in vivo (5 ± 1 ms versus 4 ± 2 ms, P = .52). Slightly longer T2 values were observed with 3D MUST‐T2 in comparison to 2D balanced SSFP T2 mapping (50.7 ± 2 ms versus 48.2 ± 1 ms, P < .05). Preliminary results in patients demonstrated T2 values in agreement with literature values.ConclusionThe proposed approach enables free‐breathing whole‐heart 3D T2 mapping with high isotropic resolution in about 8 minutes, achieving accurate and precise T2 quantification of myocardial tissue in a clinically feasible scan time.
Highlights
Quantitative myocardial T2 mapping has emerged as a promising tool for edema characterization and detection of subtle myocardial inflammation in patients with acute myocardial infarction, myocarditis, dilated cardiomyopathy, sarcoidosis, and autoimmune12 cardiomyopathies [1,2,3,4].Myocardial T2 mapping is usually performed by acquiring several ECG-triggered T2-weighted (T2w) images, with different amounts of T2 decay through T2-preparation pulses.A map of T2 relaxation times is generated by fitting the series of weighted images to an exponential decay model on a pixel-by-pixel basis
Longer T2 values were observed with 3D MUST-T2 in comparison to 2D balanced steady-state freeprecession (bSSFP) T2 mapping (50.7±2ms vs. 48.2±1ms, P
The use of 2D acquisitions with fairly thick slices and the associated partial volume effects undermine the full potential of myocardial T2 mapping, in hypertrophic cardiomyopathies where the pathological tissues are often complex threedimensional structures with differing T2 values [5,6,7]
Summary
Quantitative myocardial T2 mapping has emerged as a promising tool for edema characterization and detection of subtle myocardial inflammation in patients with acute myocardial infarction, myocarditis, dilated cardiomyopathy, sarcoidosis, and autoimmune12 cardiomyopathies [1,2,3,4].Myocardial T2 mapping is usually performed by acquiring several ECG-triggered T2-weighted (T2w) images, with different amounts of T2 decay through T2-preparation pulses.A map of T2 relaxation times is generated by fitting the series of weighted images to an exponential decay model on a pixel-by-pixel basis. Myocardial T2 mapping is usually performed by acquiring several ECG-triggered T2-. Weighted (T2w) images, with different amounts of T2 decay through T2-preparation pulses. Current clinical protocols usually perform myocardial T2 mapping with a two-dimensional (2D) single-shot steady-state free-. 24 precession sequence (T2p-SSFP), acquiring three T2-prepared images in a single-breathold. Multiple short-axis slices are usually acquired at the basal, mid-ventricular and apical level. The use of 2D acquisitions with fairly thick slices and the associated partial volume effects undermine the full potential of myocardial T2 mapping, in hypertrophic cardiomyopathies where the pathological tissues are often complex threedimensional structures with differing T2 values [5,6,7]. 2D sequences, 38 typically acquired during breath holding, regularly suffer from respiratory and cardiac motion between the T2w images, mainly due to imperfect breath-holding or variable heart rate [8]. Robust non-rigid motion-correction techniques have been proposed to correct for residual motion and improve map quality, such techniques are relatively complex, computationally expensive and only correct for in-plane motion [9,10,11]
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