MR imaging of the fetus by a HASTE sequence

The value of a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence, in which high-resolution heavily T2-weighted images can be obtained within 2 sec, was evaluated in the imaging of the fetus during the second or third trimester.

Eighteen women with complicated pregnancies as revealed on a sonogram during the second and third trimesters (16-36 weeks' gestation) were studied with a 1.5-T superconductive MR imaging unit that used a body phased-array coil. After informed consent, T1-weighted fast low-angle shot images, T2-weighted turbo spin-echo images, and HASTE images were obtained without any premedication. Images were analyzed with regard to image quality, degree of blurring, visualization of the normal fetal organs, and visualization of fetal and maternal abnormalities.

On HASTE sequences, visualization of the fetal brain, visceral organs (lung, heart, liver, kidney, and bladder), extremities, and umbilical cord were significantly better than on fast low-angle shot or turbo spin-echo sequences (p < .01). In the brain, the white matter-gray matter distinction, gyrus formation, and myelination of the brain were clearly revealed by the HASTE sequence. Pathologic processes including fetal abnormalities (anomalies of the central nervous systems [n = 5], placenta previa [n = 1], and transverse lie in the third trimester [n = 1]) and maternal abnormalities (leiomyoma [n = 5], ovarian tumors [n = 3], and hydronephrosis [n = 1]) were clearly seen on HASTE imaging. The peak specific absorption rate for RF exposure in these studies was less than 1.5 W/kg.

In situations when sonography is suggestive but not definitive, MR imaging with a HASTE sequence allows clear fetal imaging with high T2-weighted contrast.