Foetal "black bone" MRI: utility in assessment of the foetal spine

Foetal CT has recently been added to the foetal imaging armamentarium, but this carries with it the risks of ionizing radiation, both to the mother and the foetus. Foetal "black bone" MRI is a new technique that allows assessment of the foetal skeleton without the risk of exposure to ionizing radiation and is a potential new sequence in foetal MRI examination.

Retrospective review of all foetal MRI studies over the past 4- to 5-year period identified 36 cases where susceptibility weighted imaging was used. Cases were selected from this group to demonstrate the potential utility of this sequence.

This sequence is most frequently useful not only in the assessment of spinal abnormalities, most commonly the bony abnormalities in myelomeningocele, but also in cases of scoliosis, segmentation anomalies and sacrococcygeal teratoma.

Although the utility of this sequence is still being evaluated, it provides excellent contrast between the mineralized skeleton and surrounding soft tissues compared with standard half Fourier acquisition single-shot turbo-spin echo sequences. Further assessment is required to determine whether black bone MRI can more accurately evaluate the level of bony defect in spina bifida aperta, an important prognostic factor. Potential further uses include the assessment of skeletal dysplasias, evaluation of the skull base and craniofacial skeleton in certain congenital anomalies and the post-mortem evaluation of the foetal skeleton potentially obviating the need for necropsy.

Foetal black bone MRI can be performed using susceptibility weighted imaging and allows better demonstration of the mineralized skeleton compared with standard sequences.