Purpose
To 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.
Methods
The 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).
Results
Three‐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.
Conclusion
The 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.