Intrauterine diagnosis of hydranencephaly by magnetic resonance

Magnetic resonance techniques in the evaluation of the perinatal brain: recent advances and future directions

Magnetic resonance (MR) techniques are attractive for use in the developing brain because of their resolving power and their relative noninvasiveness. Their ability to provide detailed structural as well as metabolic and functional information without the use of ionizing radiation is unique. Conventional MR Imaging has widely proven its potential for identifying normal and pathologic brain morphology. Functional MR imaging such as diffusion-weighted imaging (DWI) and perfusion and blood-oxygenation-dependent BOLD imaging are newer imaging methods providing insights into brain physiology. This review will focus on the application of different MR techniques including the conventional structural MR imaging techniques and the more advanced MR techniques, such as the quantitative morphometric MR methods, the diffusion weighted MR techniques, the functional MR techniques and MR spectroscopy in the study of the fetal and newborn brain.

In vivo studies of brain development by magnetic resonance techniques

Understanding of the morphological development of the human brain has largely come from neuropathological studies obtained postmortem. Magnetic resonance (MR) techniques have recently allowed the provision of detailed structural, metabolic, and functional information in vivo on the human brain. These techniques have been utilized in studies from premature infants to adults and have provided invaluable data on the sequence of normal human brain development. This article will focus on MR techniques including conventional structural MR imaging techniques, quantitative morphometric MR techniques, diffusion weighted MR techniques, and MR spectroscopy. In order to understand the potential applications and limitations of MR techniques, relevant physical and biological principles for each of the MR techniques are first reviewed. This is followed by a review of the understanding of the sequence of normal brain development utilizing these techniques. MRDD Research Reviews 6:59-67, 2000.

Normal fetal brain development: MR imaging with a half-Fourier rapid acquisition with relaxation enhancement sequence

PURPOSE

To analyze normal maturation of the fetal brain with half-Fourier rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The normal brains of 25 fetuses of 12-38 weeks gestational age were examined in utero with half-Fourier RARE imaging. Gyrus maturation, gray and white matter differentiation, ventricle-to-brain diameter ratio, and subarachnoid space size were evaluated with respect to gestational age.

RESULTS

At 12-23 weeks, the brain had a smooth surface, and two or three layers were differentiated in the cerebral cortex. At 24-26 weeks, only a few shallow grooves were seen in the central sulcus, and three layers, including the immature cortex, intermediate zone, and germinal matrix, were differentiated in all fetuses. At 27-29 weeks, sulcus formation was observed in various regions of the brain parenchyma, and the germinal matrix became invisible. Sulcation was seen in the whole cerebral cortex from 30 weeks on. However, the cortex did not undergo infolding, and opercular formation was not seen before 33 weeks. At 23 weeks and earlier, the cerebral ventricles were large; thereafter, they gradually became smaller. The subarachnoid space overlying the cortical convexities was slightly dilated at all gestational ages, most markedly at 21-26 weeks.

CONCLUSION

Changes in brain maturation proceed through stages in an orderly and predictable fashion and can be evaluated reliably with half-Fourier RARE MR imaging.

A new tool for prenatal diagnosis: ultrafast fetal MRI

The development of ultrafast magnetic resonance imaging scanners and sequences provides a new tool for the diagnosis of fetal anomalies. Magnetic resonance imaging is a valuable adjunct to prenatal ultrasound especially for the evaluation of suspected fetal brain anomalies, chest masses, abdominal masses, and renal diseases.

Computer-assisted imaging of the fetus with magnetic resonance imaging

The purpose of this paper is to review the use of magnetic resonance imaging (MRI) of the fetus and to propose future techniques and applications. Institutional review board approved MR images of the fetus were acquired in 66 patients with sonographically suspected fetal abnormalities. Axial, coronal, and sagittal short TR, short TE images were obtained. In addition, 12 studies were performed with rapid scans requiring 700-1200 ms using either GRASS or Spoiled GRASS techniques. Sequential studies demonstrating fetal motion were also performed. Three studies with 3D IR prepped GRASS were performed. These allowed for orthogonal and non-orthogonal reformatted views and 3D display. Normal fetal structures were shown with MRI, including brain, heart, liver, stomach, intestines, and bladder. Gross fetal anomalies could generally be demonstrated with MRI. MRI may give additional information to that of sonography in fetal anomalies, particularly those involving the central nervous system, and in the detection of fat, blood, and meconium. MRI of the fetus can demonstrate normal and abnormal structures. Newer techniques with faster imaging will allow for greater possibility of computer assisted manipulation of data.

Short communication: MR imaging of fetal brain abnormalities using a HASTE sequence

HASTE (half-Fourier acquisition single-shot turbo spin echo) is a sequence that enables T2 weighted magnetic resonance (MR) images to be obtained in a few seconds. The purpose of this study was to evaluate the usefulness of this sequence in the diagnosis of fetal cerebral abnormalities. Five fetuses suspected of having cerebral abnormalities on ultrasound examination were studied by MR imaging using the HASTE sequence in utero. We compared the images with post-natal MR images or computed tomography (CT) scans. In four fetuses, the abnormality was diagnosed correctly, and the diagnosis was almost correct in the remaining fetus. This sequence is useful because it provides images of diagnostic quality in a very short scanning time.

Magnetic resonance imaging of the fetus: a study of 20 cases performed without curarization

Twenty patients underwent magnetic resonance imaging (MRI) at a mean gestational age of 32 weeks. There were 12 patients with suspected fetal brain abnormality and four with intrauterine growth retardation (IUGR), while the remaining four cases were studied for other reasons. The MRI examinations were performed on a 0.5 Tesla machine, with surface coils. One minute acquisition time T1 sequences were used. All the studies were performed without fetal curarization, and only under maternal sedation using flunitrazepam given per os 1 h before MRI examination. Three examinations were incomplete because of fetal movement artefacts. In the remaining cases, MRI allowed the examination of fetal brain anatomy. In five cases, it helped to differentiate isolated hydrocephalus and corpus callosum agenesis. Sub-ependymal nodules were depicted in a case of fetal tuberous sclerosis. One suspected arachnoid cyst was proved to be an ultrasound artefact. Decreased fetal fat on MR images was correlated with low birth weight in cases of IUGR. Due to its better spatial resolution, ultrasonography was more accurate for the diagnosis of facial and lumbar anomalies. Fetal MRI may be performed without curarization. Surface coils allow the detailed analysis of brain parenchyma, and thus MRI is especially useful in the difficult prenatal diagnosis of fetal brain abnormalities.

Prenatal diagnosis of fetal cerebral abnormalities by ultrasonography and magnetic resonance imaging

We found magnetic resonance imaging (MRI) of the fetal brain to be effective in confirming or denying diagnosis of fetal cerebral defects when ultrasonography was inconclusive or incomplete. In this paper we describe 31 cases in which ultrasonographic evidence of fetal brain defects was verified by MRI. MRI was performed after curarization of the fetus. In 21 cases, ultrasonographic evidence was confirmed by histological study of the fetus or postnatal radiological examination. In 10 cases, ultrasonographic diagnosis was denied by MRI and healthy infants were born. In one case of cerebral toxoplasmosis, ultrasonography detected periventricular calcifications but MRI was normal. In 20 cases MRI ascertained or further documented the ultrasonographic findings. However in 4 of these 20 cases autopsy of the fetus was required to determine the exact nature of the lesion.

In vivo MRI of the fetal brain

We report MRI of the brain in 45 fetuses; the findings were confirmed by pathological examination or postnatal neuroradiological studies. MRI necessitates medication to eliminate fetal motion; curare was injected into the umbilical cord, and MRI is therefore limited to cases in which umbilical cord puncture is indicated. T1-weighted images were obtained in axial, sagittal and coronal planes; the last of these were generally as the most useful as regards morphology. We demonstrated cerebral malformations (n = 13), brain haemorrhage (n = 1), a facial angioma (n = 1), a facial mass (n = 1), hydrocephalus (n = 5), unilateral ventricular enlargement (n = 1), atrophy (n = 4), a porencephalic cyst (n = 1) and normal appearances of the brain in 18 cases. Twenty-two of the fetuses were born alive, and the clinical and/or neuroradiological examination confirmed the antenatal findings. The diagnosis was also confirmed in 8 cases in which a neuropathological examination was possible.