Acquisition protocol
All patients and healthy subjects were explored using the same CMR protocol except for post contrast imaging sequences that were not performed for the latter. CMR imaging was performed with a 1.5 T CMR system (Magnetom Avanto, Siemens Healthineers, Erlangen, Germany) equipped with a high-performance gradient sub-system (maximum amplitude, 40 mT/m; minimum rise, 200 μs), and an 8-channel phased-array cardiac coil. Unenhanced cine balanced steady state free precession (bSSFP) sequences, acquired in the LV short-axis section and encompassing the entire LV were performed on all patients. The following parameters were used: TR/TE, 2.8/1.4 (apparent TR, 31.4 ms; 11 segments); flip angle, 82°; matrix size, 192 × 192; FOV, 300 × 270 mm; slice thickness, 8 mm. Retrospective electrocardiogram (ECG) gating was used with 25 phases per section.
T1 maps were acquired before injection (myocardial native T1) and 15 min after gadolinium administration (0.2 mmol/Kg of gadolinium (Dotarem; Guerbet; Aulnay-sous-Bois; France)) in all the patients in a middle short-axis and in the four-chamber planes using the modified Look-Locker inversion recovery (MOLLI) sequence [
25]. The following parameters were used: 3 inversion sets of 3/3/5 images, TE/TR = 1.06/2.5 ms, nominal flip angle = 35°, TI
1 = 100 ms, DTI = 80 ms, matrix = 192 × 154, FOV = 340 × 274 mm
2, BW = 930 Hz/pixels, slice thickness = 8 mm, generalized autocalibrating partially parallel acquisition (GRAPPA) 2 with 36 separated reference lines, 75% of partial Fourier, 3 R-R cycles recovery period and an acquisition time = 17 R-R cycles. T2 maps were generated using a non-product bSSFP sequence with an adiabatic T2 preparation, and acquired at the same location as T1 maps. The following parameters were used: TE/TR = 1.12/2.6 ms, 3 T2-preparation times = 0/25/55 ms, matrix = 192 × 154, FOV = 340 × 154, BW = 930 Hz/pixels, slice thickness = 6 mm, GRAPPA 2 with 36 separated reference lines, 75% of partial Fourier, acquisition time = 12 R-R cycles. All images were acquired within a single breath hold. A fast variational non-rigid registration algorithm was used to correct for residual cardiac and respiratory motion between images, aligning all T1- and T2-prepared frames to the center frame. Finally, T1 and T2 maps were generated from these motion-corrected images by fitting a mono-exponential decay curve at each pixel. A short Tau inversion recovery (STIR) T2-weighted image was acquired in the middle short axis section at the same level as T1 and T2 maps using the following parameters: TE/TR = 49/1500 to 2500 ms (depending on the heart rate), matrix = 192 × 154; field-of-view (FOV) = 340 × 154, BW = 255 Hz/pixel, slice thickness = 8 mm, turbo factor 15 and TI 150 ms. A surface coil intensity correction algorithm was used to compensate the myocardial intensity inhomogeneity.
LGE images covering the LV in short-axis and long-axis views were obtained 10 min after injection of 0.2 mmol/Kg of gadolinium (Dotarem; Guerbet; Aulnay-sous-Bois; France) in all the patients. A segmented 3D IR gradient-echo T1-weighted sequence was used with the following parameters: repetition time of 3.9 ms, echo time of 1.4 ms, flip angle of 10°, matrix size of 192 × 192, FOV 300 × 270 mm, 12 sections, and 6 mm slice thickness. Image acquisition lasted between [12 to 20 s] depending on the heart rate. A dedicated inversion recovery time (TI) scouting sequence was used before acquisition of LGE images to adjust the optimal TI. Phase sensitive inversion recovery (PSIR) images were systematically acquired after acquisition of LGE images because suboptimal nulling of the myocardial signal may be encountered in CA [
26]. Sequence parameters of the PSIR sequence were as follows: repetition time of 835 ms, echo time of 3.3 ms, flip angle of 10°, matrix size of 256 × 156, FOV 300 × 270 mm, and 8 mm slice thickness. Image acquisition lasted between 8 to 12 s, depending on the heart rate. Five PSIR images were acquired in the short-axis plane encompassing the LV. One slice was also acquired in the 4-chamber and in the 2-chamber view.