Fetal magnetic resonance hydrography: evaluation of a single-shot thick-slab RARE (rapid acquisition with relaxation enhancement) sequence in fetal thoracoabdominal pathology

Abstract

To evaluate the potential of a single-shot thick-slab RARE (rapid acquisition with relaxation enhancement) sequence in fetal thoracoabdominal magnetic resonance (MR) examinations compared with multislice T2-weighted sequence and postnatal imaging. RARE sequence is rapid and provides very heavily T2-weighted images. Twenty-seven fetal thoracoabdominal MR imaging examinations were performed at 23-38 weeks using our conventional protocol. This included thin multislice T2-weighted half-Fourier acquired single-shot turbo spin-echo (HASTE) sequence and thin-slice GE (gradient echo) T1-weighted images with a 1.5-T MR unit. A single-shot thick-slab (60 mm) RARE sequence was added to all MR examinations. The acquisitions were obtained with the mother breath-holding. The thick-slab heavily T2-weighted images were compared with HASTE sequence images and with postnatal imaging in all cases. The thick-slab RARE sequence did not show additional abnormalities compared with the conventional protocol but displayed an overall view of the urinary tract, tracheobronchial tract and small bowel. It gave information that was highly correlated with postnatal imaging, such as abdominal plain films, chest film or cystography. The quality of the thick-slab RARE images was considered as good in 13 cases (48%), moderate in 12 cases (45%) and poor in two cases (7%). Although thick-slab RARE sequence does not show additional abnormalities compared with the conventional protocol, it illustrates very nicely static fluids such as those in urinary dilatation, the esophagus and small bowel (normal or dilated) and thoracic cystic masses. It is very rapid (5 s) to perform, allows fetal hydrography, and correlates well with postnatal imaging.