Magnetic resonance imaging of the fetus

This paper discusses the current role of fetal brain MR during pregnancy for the purposes of prenatal diagnosis. A short history of the method is outlined since its first applications in the early Eighties. The major problems surrounding fetal MR in literature reports are the medical and legal issues linked to the biological effects of MR and the technical problems of poor imaging caused by fetal movements. Following a broad consensus that MR is safe for the fetus, scans performed in the last decade have generally been authorized by local ethical committees. Solving the problem of artifacts caused by fetal movements has proved more arduous. Simple precautions are usually implemented (a special maternal posture during the scan, prolonged fasting by the mother, administration of diazepam to the mother) or more invasive measures such as curarization of the fetus by echo-guided intramuscular or transfunicular injection of a curare-like drug. Other solutions include adopting ultrafast sequences (Echo Planar), only possible with special MR software. Our own method is presented with a series of 27 women 19 to 38 weeks pregnant, all with an ultrasound diagnosis of fetal malformation. Generally speaking, the preferred solution to eliminate fetal movements was fetal curarization (22 cases) and the different drugs and doses administered are listed. In the 5 scans performed without fetal curare, the patient was asked to lie on her left side. Examination techniques include short TR Spin Echo sequences for T1 weighted images (16 cases) and short TR 2D Gradient Echo Flash sequences (10 cases); long TR and short and long TR Spin Echo sequences were tested in one case. Appropriately oriented presaturation impulses were essential in all cases. The results are discussed in terms of MR image quality and pregnancy outcome. The different malformation patterns encountered will be discussed in another paper. Here, we present a revised normal fetal head anatomy extrapolated from MR images of abdominal disease (4 cases) and two cases in which fetal MR was at variance with the ultrasound diagnosis disclosing a normal fetal brain. The anatomy of the cerebral ventricles is described focussing on physiological dilatation of the lateral ventricles during the second trimester of pregnancy and the morphology of the fetal cisternae. The development of the brain and structures in the posterior cranial fossa is discussed in different gestational stages with particular reference to the signals emitted by different brain tissues, the problem of neuronal migration and relative gyration and incipient myelinization. To conclude, we present some chance MR images of fetal spine