Vanessa Berger-Kulemann

¹H MR spectroscopy (MRS) has been established as a useful adjunct tool for morphologic imaging of the brain to understand the pathophysiologic mechanisms of fetal brain injury. The intrinsic magnetic properties of the fetal brain are used to compile a spectrum that contains different signal peaks, based on identifiable metabolites. The composition of these metabolites may indicate abnormalities in fetal brain metabolism, such as those that occur in developmental disorders, inborn errors of metabolism, and hypoxic encephalopathy.

We chose this topic because the quality of spectroscopic studies strongly depends on the homogeneity of the magnetic field, and may be limited because of unrestricted fetal movements during the acquisition of the scan. To avoid these motion artifacts, fetal sedation is recommended in the literature. However, even with a single maternal dose of a benzodiazepine, adverse effects, such as impairment of psychomotor functions and cognitive functions, with a lack of concentration and confusion, and other effects, including gastrointestinal disturbances, are possible. The mother must be monitored after the MRI examination, which is an organizational problem at most busy radiology departments. Furthermore, fetal behavior cannot be evaluated reliably in sedated fetuses and may impair the neurologic assessment of the fetus.

Nevertheless, based on our routine clinical experience, fetal sedation is usually not necessary. Therefore, we aimed to assess the feasibility and quality of brain ¹H MRS in unsedated fetuses and to evaluate whether the quality of the examination is dependent on the type of spectra (short/long echo time), fetal presentation, gestational age, and/or fetal pathology. We evaluated 75 spectra, statistically analyzed the impact of the different parameters on the quality of the spectra, and discovered that ¹H MRS of the brain can be performed in about two-thirds of unsedated fetuses after gestational week 19, regardless of the type of spectra, fetal presentation, gestational age, or pathology.

The results of our study confirmed our daily experience, and we routinely perform our fetal MR examinations without any fetal sedation. Due to more complicated baselines, spectral patterns, and possible lipid contamination, short TE spectra of the fetal brain are definitely more prone to be unreadable. Therefore, we measure the long TE spectra first, and, if the quality is satisfactory, then the short TE spectra.

We continue to perform brain MRS to investigate abnormalities in fetal brain metabolism in various types of fetal pathology. Because MRS provides important in vivo information about the metabolic status of diverse fetal tissues aside from the fetal brain, we also study the feasibility and clinical utility of different MRS techniques with fetal whole-body MRI.

Read this article at AJNR.org …