Magnetic resonance methods in fetal neurology M. Mailath-Pokorny a, * , G. Kasprian b , C. Mitter b , V. Schöpf b , U. Nemec b , D. Prayer b a Medical University of Vienna, Department of Obstetrics and Gynecology, Vienna, Austria b Medical University of Vienna, Department of Radiodiagnostics, Vienna, Austria Keywords: Fetus Functional magnetic resonance imaging Magnetic resonance imaging Neurology Spectroscopy Tractography summary Fetal magnetic resonance imaging (MRI) has become an established clinical adjunct for the in-vivo evaluation of human brain development. Normal fetal brain maturation can be studied with MRI from the 18th week of gestation to term and relies primarily on T2-weighted sequences. Recently diffusion- weighted sequences have gained importance in the structural assessment of the fetal brain. Diffusion- weighted imaging provides quantitative information about water motion and tissue microstructure and has applications for both developmental and destructive brain processes. Advanced magnetic resonance techniques, such as spectroscopy, might be used to demonstrate metabolites that are involved in brain maturation, though their development is still in the early stages. Using fetal MRI in addition to prenatal ultrasound, morphological, metabolic, and functional assessment of the fetus can be achieved. The latter is not only based on observation of fetal movements as an indirect sign of activity of the fetal brain but also on direct visualization of fetal brain activity, adding a new component to fetal neurology. This article provides an overview of the MRI methods used for fetal neurologic evaluation, focusing on normal and abnormal early brain development. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Overview Fetal neurology has been defined as morphological, metabolic and functional assessment of the fetus. 1 Ultrasound has been the primary imaging method for the routine evaluation of the fetus and for the early diagnosis of fetal malformations. 2 To date, morpho- logical and functional information has been acquired mainly by ultrasound, 3 which is still the mainstay of imaging the fetus. 4 According to its specific physical background, ultrasound is limited to the visualization of only certain aspects of fetal neuro- logical diseases. Fetal magnetic resonance imaging (MRI) has evolved in the last 25 years since it was first described 5 and has become of increasing importance as an adjunct to prenatal ultrasound, 6 especially when evaluating the fetal brain. 7 Because of its higher tissue contrast resolution than prenatal sonography it allows better visualization of both normal and abnormal tissue 7 and may add important information in three specific ways: by quantification of brain growth and structural abnormalities, by qualitative evaluation of central nervous system (CNS) microstructure and by qualitative assessment of dynamic fetal movements in utero. 8 Thus, using MRI as a clinical adjunct to ultrasound, all three mentioned areas of neurologic evaluation can be approached. Normal fetal brain maturation can be studied by in-vivo MRI from the 18th week of gestation to term and relies primarily on T2- weighted sequences. Diffusion-weighted sequences have recently gained importance in the structural assessment of the fetal brain. Diffusion-weighted imaging provides quantitative information about water motion and tissue microstructure and has applications for both developmental and destructive brain processes. 9,10 Advanced magnetic resonance techniques, such as spectroscopy, might be used to demonstrate metabolites involved in brain maturation, 11 though their development is still in the early stages. Regarding functional assessment, two possibilities exist: similarly to ultrasound, MRI may record gross and intrinsic fetal move- ment, 12 and MRI may directly assess brain function. 13 1.2. Safety of MRI in human studies It is generally accepted that MRI is safe in pregnancy since no short- or long-term effects of MRI on mother or fetus have been reported. Concerns have been raised in some studies about the level of acoustic noise, biological effects and static field exposure. 2 However, several studies failed to show any adverse long-term * Corresponding author. Address: Medical University of Vienna, Department of Obstetrics and Gynecology, Waehringer Guertel 18e20, 1090 Vienna, Austria. Tel.: þ431 40400 2821; fax: þ431 40400 2862. E-mail address: mariella.mailath-pokorny@meduniwien.ac.at (M. Mailath- Pokorny). Contents lists available at SciVerse ScienceDirect Seminars in Fetal & Neonatal Medicine journal homepage: www.elsevier.com/locate/siny 1744-165X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.siny.2012.06.002 Seminars in Fetal & Neonatal Medicine 17 (2012) 278e284