3D whole‐heart isotropic‐resolution motion‐compensated joint T<sub>1</sub>/T<sub>2</sub> mapping and water/fat imaging
Giorgia Milotta, Aurélien Bustin, Olivier Jaubert, Radhouène Neji, Claudia Prieto, René M. Botnar
Abstract
Purpose To develop a free‐breathing isotropic‐resolution whole‐heart joint T 1 and T 2 mapping sequence with Dixon‐encoding that provides coregistered 3D T 1 and T 2 maps and complementary 3D anatomical water and fat images in a single ~9 min scan. Methods Four interleaved dual‐echo Dixon gradient echo volumes are acquired with a variable density Cartesian trajectory and different preparation pulses: 1) inversion recovery‐preparation, 2) and 3) no preparations, and 4) T 2 preparation. Image navigators are acquired to correct each echo for 2D translational respiratory motion; the 8 echoes are jointly reconstructed with a low‐rank patch‐based reconstruction. A water/fat separation algorithm is used to obtain water and fat images for each acquired volume. T 1 and T 2 maps are generated by matching the signal evolution of the water images to a simulated dictionary. Complementary bright‐blood and fat volumes for anatomical visualization are obtained from the T 2 ‐prepared dataset. The proposed sequence was tested in phantom experiments and 10 healthy subjects and compared to standard 2D MOLLI T 1 mapping, 2D balance steady‐state free precession T 2 mapping, and 3D T 2 ‐prepared Dixon coronary MR angiography. Results High linear correlation was found between T 1 and T 2 quantification with the proposed approach and phantom spin echo measurements ( y = 1.1 × −11.68, R 2 = 0.98; and y = 0.85 × +5.7, R 2 = 0.99). Mean myocardial values of T 1 /T 2 = 1116 ± 30.5 ms/45.1 ± 2.38 ms were measured in vivo. Biases of T 1 /T 2 = 101.8 ms/−0.77 ms were obtained compared to standard 2D techniques. Conclusion The proposed joint T 1 /T 2 sequence permitted the acquisition of motion‐compensated isotropic‐resolution 3D T 1 and T 2 maps and complementary coronary MR angiography and fat volumes, showing promising results in terms of T 1 and T 2 quantification and visualization of cardiac anatomy and pericardial fat.