CMR examination was performed on a 1.5T clinical scanner with a dedicated receive-only 32-channel phased-array cardiac surface coil (Discovery MR450, GE Healthcare, Milwaukee, WI, USA). The animals were sedated, and intubated as described above. Anesthesia during imaging was maintained with pentobarbital sodium (6–12 mg/kg/h). Mechanical ventilation and breath-holds were performed using a mobile ventilator (Carina™, Dräger Medical, Best, The Netherlands). Heart rate (HR) and blood pressures were monitored throughout the scan. When necessary, and always in absence of pain reflexes, muscle relaxation was achieved using pancuronium bromide (2–4 mg bolus). The image protocol consisted of 2D balanced Steady-State Free Precession (SSFP) cine imaging, 4D flow, and 2D phase contrast flow measurements. Standard long-axis and short-axis images with full left ventricular (LV) coverage were acquired using retrospectively ECG-gated SSFP cine imaging with breath-holding (FIESTA, GE Healthcare acronym). Typical scan parameters were slice thickness 6.0 mm, slice gap 0 mm, TR/TE 3.4/1.4 ms, flip angle (FA) 75°, field of view (FOV) 320 × 240 mm, acquired matrix 128 × 180, and reconstructed to a pixel size of 1.3 × 1.3 mm. The free-breathing, retrospectively ECG-gated 4D flow acquisition was performed directly after administration of a gadolinium-based contrast agent (Gadovist 1.0 mmol/mL, Bayer, Mijdrecht, The Netherlands, single dose of up to 15 mL). The 4D flow sequence has been described before [
11‐
13], in short the sequence was prescribed in axial plane, including the entire thorax in the field of view. The k-space was filled with variable-density Poisson-disc undersampling with acceleration factors of 1.8 × 1.8 (phase × slice) and the parallel imaging algorithm used was ESPIRiT. The following imaging parameters were used: matrix 192 × 160 × 78, acquired resolution 2.1 × 1.7 × 2.8 mm, reconstructed resolution 2.1 × 1.7 × 1.4 mm, TR/TE 3.8/1.5 ms, FA 15°, views per segment 4, bandwidth 63 kHz, number of reconstructed phases 20 per cardiac cycle, and a velocity encoded value set at 250 cm/s. Scan time ranged between 5.57 and 8.51 min. Finally, one-directional through plane 2D phase contrast flow measurements of the aorta (at the level of the aortic valve or just above) and pulmonary artery were performed during an end-expiratory breath-hold. The imaging planes were planned perpendicular to the great vessels. Typical scan parameters were slice thickness 6.0 mm, matrix 256 × 166, TR/TE 4.0/2.2 ms, FA 18°, FOV 340 × 220, velocity encoding value set at 180 cm/s. The invasive flow probe was attached to the amplifier and a flow signal was obtained immediately before and after the 4D flow CMR sequence.