MR fetography using heavily T2-weighted sequences: comparison of thin- and thick-slab acquisitions

To evaluate the use of MR-fetography sequences in identifying the major fetal structures and to compare thick- and thin-slab acquisitions for their diagnostic value.

Twenty-one consecutive, pregnant women with suspected fetal pathology underwent fetal magnetic resonance imaging (MRI) using a 1.5 T MRI unit. Heavily T2-weighted, single-shot fast spin-echo (SSFSE) sequences with a long echo train (MR-fetography) were acquired in a thick- and thin-slab modus. Thick- and thin-slab acquisitions were reviewed by two experienced radiologists with regard to the overall image quality and landmark anatomical structures (spinal canal, spinal cord, posterior fossa, cerebellum, brainstem, basal cisterns, stomach, urinary bladder and umbilical cord according to a three-scale grading system (good, moderate and poor). Visibility scores were calculated and compared between both sequences.

Overall image quality was graded good in 76.2%, moderate in 19.0% and poor in 4.8% for thick-slab images and good in 81%, moderate in 14.3% and poor in 4.8% for thin-slab images. The visibility scores of the thick/thin-slab images for evaluation of the main fetal structures were as follows: for the spinal canal 2.8+/-0.4/2.9+/-0.54 (p>0.05), spinal cord 2.4+/-0.75/2.7+/-0.66 (p>0.05), posterior fossa components (cerebellum, brainstem and basal cisterns) 2.4+/-0.68/2.8+/-0.54; 2.4+/-0.67/2.7+/-0.66; 2.5+/-0.51/2.7+/-0.56 (p<0.05), stomach 2.8+/-0.44/2.9+/-0.48 (p>0.05), urinary bladder 2.8+/-0.51/2.8+/-0.54 (p>0.05) and umbilical cord 2.9+/-0.30/2.6+/-0.60 (p<0.05).

Heavily T2-weighted MR-fetography renders a quick overview of fetal contours, fetal position, amount of amniotic fluid and integrity and presence of several major fluid containing structures. Thick- and thin-slab acquisitions render complementary information. Thick-slab images display the entire fetus in one projection while thin-slab images provide more detailed anatomical information. The short imaging time usually allows measuring both thick- and thin-slab images. MR-fetography is as a helpful addition to conventional fetal MRI. MR-fetography should not be viewed as a single, stand alone sequence but as a supporting fast MR sequence in a well-designed multisequence fetal MRI protocol. Future studies evaluating larger patient groups are mandatory.