Anne-Marie Koop

206 3.3.7. Sweep the probe minimally towards the left so the ascending aorta disappears behind the pulmonary artery. The appropriate PLAX is identifiedwhen the pulmonary artery is visualized, with blood flowing vertically. 3.3.8. Place the cursor in line with the pulmonary artery. Press the continuous wave (CW) Doppler button to derive velocity time integral measurements during three cardiac cycles. Press Save . 3.3.9. Rotate the probe 90° clockwise from the PLAX to obtain PSAX, then tilt the probe slightly towards the cranial/ventral direction to derive the PSAX at the aortic level. The appropriate PSAX view is identified if the RV outflow tract is situated between the aorta and the probe. This continues in the pulmonary artery, with blood flowing vertically. For a detailed description see Cheng et al. 48 3.3.10. Place the cursor in line with the pulmonary artery. Press the continuous wave (CW) Doppler button to derive velocity time integral measurements during three cardiac cycles. Press Save . 3.3.11. Measure the three maximum velocities of the best view (PSAX or PLAX) and calculate the mean. Use the simplified Bernoulli’s principle delta-P = 4 · V² to derive the PAB gradient in millimeters mercury (mmHg). 4. Cardiac magnetic resonance imaging 4.1. Preparation 4.1.1. Perform CMR analysis 6 weeks (i.e., 42 days) after PAB surgery. NOTE: Additionally, earlier timepoints after PAB surgery may be chosen when multiple timepoints are to be included, depending on the research question. Later timepoints could be considered; however, RV failure and death may increasingly occur. 4.1.2. Use a sufficiently powerful magnet (typically, >7 T is used for rodent CMR scanning). For the current protocol, a 9.4 T vertical system, with 1,500 mT/m gradient set and 89 mm bore size is used. 4.1.3. Install CMR postprocessing software for analyzing volumes and masses in the derived images. The software is deemed appropriate if it allows manual segmentation to determine end-diastolic (ED) and end-systolic (ES) volumes (EDV and ESV, respectively) and ventricular mass (measured both ED and ES).