Mr450 1.5 t scanner

All MR imaging was performed on a GE MR450 1.5 T scanner using an 8-channel cardiac array coil. Pregnant subjects were scanned either in the supine or lateral decubitus position depending on the patient size and their preference. In each study, 2D T2-weighted single-shot fast spin echo imaging was performed for anatomical imaging and 3D VSASL was performed for the measurement of placental perfusion. This approach of placental perfusion imaging has been previously described and demonstrated to be superior in comparison with conventional ASL in our preliminary study¹⁵ . T2-weighted imaging utilized the scan parameters of TR/TE = 1200/160 ms, matrix size = 256 × 192, FOV = 36–42 cm, and slice thickness = 4 mm with 40–60 slices. In VSASL, velocity-selective labeling was achieved using dual hyperbolic secant (sech) inversion with a cutoff velocity = 2 cm/s and TI = 1600 ms. Image acquisition in VSASL was performed using fast-spin-echo 3D stack of spirals with 8 interleaves, TR/TE = 3000/10 ms, in-plane matrix size = 64 × 64 over FOV = 36–40 cm, and slice thickness = 4 mm with 36–44 slices. Background suppression was achieved using one saturation and four sech inversion pulses. VSASL scan was composed of five pairs of control/labeled imaging followed by proton-density imaging, leading to total scan time of 4:30 min.