MRI examination
At the University Hospitals Leuven MRI was performed as being part of standard clinical care using a clinical 1.5 Tesla system (Siemens Aera; Siemens, Erlangen, Germany). Two small body coils were placed adjacent to each other over the maternal abdomen. The mother was positioned in the supine or left lateral decubitus position. Prior to September 2015, maternal sedation (flunitrazepam 0.5 mg per os 20 – 30 minutes prior to the examination) was used when GA was under 30 weeks, a practice that was since abandoned. 13, 14 . The protocol includes T2-weighted half-Fourier acquired single-shot turbo spin-echo (HASTE) sequences, obtained in three orthogonal planes relative to the fetal head (coronal ,axial and sagittal). Scanning parameters were echo time (TE) 133ms; repetition time (TR) 1,000ms; slice thickness (ST) 3.0–4.0mm; absence of intersection gap; and field of view (FOV) 300 x 300 - 380×380 mm. Fetal body imaging was performed with T2-weighted HASTE sequences, obtained in three orthogonal planes relative to the fetal body (coronal, axial and sagittal). Scanning parameters were TE 90ms; TR 1000ms; ST 3.0–4.0mm; absence of intersection gap; and FOV 300 x 300 - 380×380 mm. Parameters from the MRI examination in controls scanned at the Robert Steiner MRI Unit in Hammersmith Hospital, London, UK were similar and can be found in Kyriakopoulou et al.12
These examinations were performed using a 1.5 T MRI System (Philips Achieva; Philips Medical systems, Best, the Netherlands) with a 32-channel cardiac array coil. The mother was positioned in a left lateral tilt, no sedation was used. The images used for this study included T2-weighted images in transverse, sagittal, and coronal planes. T2-weighted Single Shot Turbo Spin Echo sequence was acquired using the following scanning parameters: TE = 160 ms, TR = 15,000 ms, ST 2.5 mm, slice overlap of 1.5 mm.8