Fetal MRI of the central nervous system: State-of-the-art

Prenatal ultrasonographic (US) examination is considered as the first tool in the assessment of fetal abnormalities. However, several large-scale studies point out that some malformations, in particular central nervous system (CNS) anomalies, are not well characterized through US. Therefore, the actual malformation severity is not always related to prenatal ultrasound (US) findings.Over the past 20 years, ultrafast Magnetic Resonance Imaging (MRI) has progressively increased as a prenatal 3rd level diagnostic technique with a good sensitivity, particularly for the study of fetal CNS malformations. In fact, CNS anomalies are the most common clinical indications for fetal MRI, representing about 80% of the total examinations.This review covers the recent literature on fetal brain MRI, with emphasis on techniques, safety and indications.     

Magnetic resonance imaging of the fetal lung: a pictorial essay

Ultrasound, which is now a widely available and generally accepted, low-cost technique with real-time properties, is the screening investigation of choice in fetal medicine. However, enthusiasm for fetal prenatal magnetic resonance imaging (MRI) is rising, because of the absence of known biological risks, the increasing ease of performing of fetal MRI and the superb contrast resolution provided. Over the last 10 years, the technology has advanced dramatically. Fast imaging sequences have allowed better MRI visualization of the unborn patient than ever before. As a consequence, experience with fetal MRI is gradually expanding. We are beginning to appreciate the clinical conditions where fetal MRI can complement the ultrasound findings. Apart from the central nervous system, MRI of the fetal lung has received the most attention. Fetal MRI can be used to assess thoracic structural anomalies, lung development as well as maturation. The introduction of fetal therapy for severe lung hypoplasia, associated with congenital diaphragmatic hernia (CDH), has recently boosted the application. This review aims to highlight MRI techniques used to image the lungs of the unborn child and to point out their strengths and limitations in specific conditions.     

Fetal magnetic resonance imaging of the brain: technical considerations and normal brain development

Fetal MRI examines non-invasively the unborn fetus. Ultrafast MRI sequences effectively suppress fetal motion. Multiple case reports and studies have shown that fetal MRI is particularly helpful in the evaluation of the central nervous system. The high contrast-to-noise ratio, the high spatial resolution, the multiplanar capabilities, the large field of view and the simultaneous visualisation of fetal and maternal structures have proven to be advantageous. Fetal MRI is particularly helpful in the evaluation of the normal and pathological development of the brain. Despite the fact that no side effects have been reported or are to be expected, the use of MRI during pregnancy is still limited to the second and third trimester of pregnancy. Magnetic resonance imaging contrast media are not to be used as it passes the placenta. Ultrasound remains the primary screening modality for fetal pathology; fetal MRI can serve as an adjunct or second-line imaging modality.     

Prenatal magnetic resonance imaging: brain normal linear biometric values below 24 gestational weeks

Introduction  Prenatal magnetic resonance (MR) imaging is currently used to measure quantitative data concerning brain structural development. At present, morphometric MR imaging studies have been focused mostly on the third trimester of gestational age. However, in many countries, because of legal restriction on abortion timing, the majority of MR imaging fetal examination has to be carried out during the last part of the second trimester of pregnancy (i.e., before the 24th week of gestation). Accurate and reliable normative data of the brain between 20 and 24 weeks of gestation is not available. This report provides easy and practical parametric support to assess those normative data. Materials and methods  From a database of 1,200 fetal MR imaging studies, we retrospectively selected 84 studies of the brain of fetuses aged 20–24 weeks of gestation that resulted normal on clinical and radiological follow-up. Fetuses with proved or suspected infections, twin pregnancy, and fetuses of mothers affected by pathology that might have influenced fetal growth were excluded. Linear biometrical measurements of the main cerebral structures were obtained by three experienced pediatric neuroradiologists. Results  A substantial interobserver agreement for each measurements was reached, and normative data with median, maximum, and minimum value were obtained for brain structures. Conclusion  The knowledge of a range of normality and interindividual variability of linear biometrical values for the developing brain between 20th and 24th weeks of gestation may be valuable in assessing normal brain development in clinical settings.     

磁敏感加权成像在中枢神经系统的临床应用

磁敏感加权成像是包含相位图像和幅度图像的三维、高分辨、完全流速补偿的梯度回波序列,对静脉结构和血液代谢物十分敏感。本文就其原理和及其在脑血管畸形、脑血管病、脑肿瘤、脑外伤、神经变性病等中枢神经系统病变中的临床应用进行综述。     

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.     

Magnetic resonance imaging phase encoding: a pictorial essay

A set of MRI images with various degrees of phase encoding were generated from the same raw data set. The resultant pictorial teaching aid is useful in developing an intuitive understanding of the mechanics and principles of phase encoding in two dimensional, Fourier transform magnetic resonance imaging.     

Nuclear magnetic resonance imaging in central nervous system disease

From the preliminary work of many investigators, it appears that proton nuclear magnetic resonance (NMR) imaging will have wide application in the diagnostic assessment (and potential management) of patients with vascular, neoplastic, and demyelinating diseases of the central nervous system (CNS). Findings in isolated cases and small series suggest that NMR imaging may play a role in the evaluation of patients with other CNS conditions including hydrocephalus, malformations, infections, developmental and metabolic disorders, and degenerative processes. Because of the dynamic nature of disease processes involving the CNS, the precise meaning of NMR image parameters (rho, T1, and T2) remains unclear. A comprehensive study correlating NMR images in neurologic disease with precise neuropathologic examination is required. In the future, with accurate quantitative measurements of these NMR parameters, in vivo imaging may provide insight into the dynamic nature of neurologic disease.     

Isolated acromioclavicular joint pathology in the symptomatic shoulder on magnetic resonance imaging: a pictorial essay

The acromioclavicular (AC) joint is a synovial joint that is predisposed to painful syndromes because of mechanical stress or developmental variation. It is often overlooked in the evaluation of patients with shoulder pain, however. Isolated AC joint pathology was studied on magnetic resonance imaging scans of patients with symptoms suggesting rotator cuff pathology. The conditions identified included osteoarthritis, distal clavicle osteolysis, and os acromiale syndrome.     

Magnetic resonance imaging of spinal cord trauma: a pictorial essay

Assessing a patient with clinical signs of acute spinal cord trauma is an emergency. A radiological work-up is crucial in determining management, and magnetic resonance imaging (MRI) is the modality of choice. It should therefore be performed immediately, preferably within 3 hours, even when plain radiography does not show an abnormality. By choosing an appropriate imaging protocol, it is possible to assess the spinal cord, joints, muscles, ligaments and bone marrow of the spine. Moreover, early MRI findings assist in determining functional prognosis. A major limitation to early MRI is that the examination is usually restricted to stable trauma patients because of the difficulties in monitoring ventilated patients during scanning. However, when an anaesthesiologist with experience in MRI and MR-compatible monitoring equipment is available, even these patients can be safely examined. MRI is also indicated for the evaluation of patients with late complications and sequelae following spinal cord trauma, since many of these chronic lesions are potentially treatable.     

Contrast-enhanced magnetic resonance imaging of tumours of the central nervous system: a clinical review

The clinical application of the intravascular paramagnetic contrast agent gadolinium-DTPA for magnetic resonance imaging (MRI) imaging of tumours of the central nervous system (CNS) has been assessed over the past 3 years. Various patterns of contrast enhancement were observed, and situations in MRI where the administration of contrast medium may be useful have been defined. These include lesions which are isointense with normal brain matter, the separation of tumour from surrounding oedema, evaluation of the degree of blood-brain barrier breakdown, delineation of tumours obscured by overlying calcification on computed tomography (CT) and in the investigation of lesions in anatomical areas where CT has known limitations (brain stem, cervical spine). Changes in relaxation times in normal and abnormal tissues following contrast medium, toxicity and dosage of gadolinium-DTPA, and MRI pulse sequence techniques are reviewed.     

Gd DTPA: a review of clinical indications in central nervous system magnetic resonance imaging

Since its approval for clinical use in mid 1988, Gd DTPA has found widespread application as a contrast agent in MRI. This paramagnetic metal ion chelate is used primarily for enhancement of head and spine lesions. Indications for contrast agent use in MRI are summarized drawing upon experience in more than 600 patients and a review of the literature. Enhancement improves both lesion detection and categorization. In head examinations, we recommend use of Gd DTPA for studies of the internal auditory canal, metastatic disease, infarction, infection, meningeal disease, and primary neoplastic disease. In spine examinations, contrast enhancement is employed both for detection of neoplastic disease and in the postoperative back for the differentiation of scar from recurrent disk herniation. Gd DOTA and Gd DO3A-R are new agents within this same class of contrast media.     

Unusual extra-axial central nervous system involvement of non-Hodgkin's lymphoma: magnetic resonance imaging

The MR imaging findings in a patient with non-Hodgkin's lymphoma with unusual involvement of the sella, pituitary stalk and left parasellar region are reported here. On the basis of the MR imaging findings, the initial differential diagnosis included invasive pituitary adenoma, a granulomatous lesion and en plaque meningioma. Trans-sphenoidal biopsy of the sellar mass showed chronic inflammatory changes and the patient was initially treated for tuberculosis. Because follow-up imaging showed the lesion to be progressive, a biopsy was done of an enlarged right inguinal lymph node. This revealed non-Hodgkin's lymphoma.     

Rounding of the hippocampus in Alzheimer's disease: a study by routine coronal magnetic resonance imaging

Purpose On routine coronal images, we have recognized atrophied hippocampi that appear round in patients with Alzheimer's disease (AD). The purpose of this study was to evaluate rounding of the hippocampus in patients with AD and to elucidate whether this change is a useful radiological marker of atrophy of the hippocampus. Materials and methods We enrolled 14 patients with moderate AD (Mini-Mental State Examination score 16.2 ± 3.3) and 15 patients without dementia or neurological deficits as the control group. For measurement of the hippocampus, we used T2-weighted coronal images parallel to the floor of the fourth ventricle. Two observers measured the dimensions of the long and short axes of the hippocampal body of 28 hippocampi from 14 patients with AD and 30 hippocampi from 15 controls. As a marker of rounding of the hippocampal body, we calculated the ratio of the short axis length to the long axis length (the rounding ratio) of the hippocampus. Results We observed apparent atrophy of the long axis of the hippocampus in patients with AD. An unpaired t-test indicated significant differences in the long axis length and the rounding ratio between the control and AD groups (P < 0.01) in the measurements of both observers. However, there was no significant difference in the short axis length. With a threshold of 0.7 in the rounding ratio, the sensitivity was 85.7% and the specificity was 66.7%. Conclusion The hippocampus appears round on coronal images in the presence of moderate AD. The rounding ratio of the hippocampus is a useful and facile indicator of hippocampal atrophy.     

原发性中枢神经系统血管炎的高分辨率MRI表现

目的探讨HR-MRI对原发性中枢神经系统血管炎(PACNS)的诊断价值。方法分析24例PACNS患者的临床和MRI资料,分析HR-MRI影像学表现。结果在HR-MRI上24例PACNS患者中,存在43个病变,可见管壁环周增厚36个、管壁偏心性增厚7个。管壁内壁均光滑。外壁模糊38个、外壁清晰5个。33个病变可见管壁向心性增强,7个病变管壁偏心性增强,无强化3个。病变累及血管壁的长度中位长度为5.4 mm(范围3.0~7.8 mm),病变部位血管壁厚度的中位厚度为0.69 mm(范围0.52~0.85 mm)。结论高分辨率磁共振成像能够清晰显示受累血管的管壁环周增厚、内壁光滑和外壁模糊、血管壁向心性强化,对PACNS的鉴别诊断有很大的作用。     

Magnetic resonance imaging of the wrist in early rheumatoid arthritis: a pictorial essay

This pictorial essay describes the changes seen in the wrist in early rheumatoid arthritis (RA) on MRI. Magnetic resonance imaging can demonstrate bone erosions, bone marrow signal changes, synovitis and tenosynovitis in early rheumatoid arthritis. Magnetic resonance imaging of the wrist can identify erosions in RA earlier than plain radiographs and can detect more erosions. Common sites include the capitate, lunate and scaphoid. Bone marrow signal changes occur frequently and are most common in the capitate, lunate and triquetrum. Synovial thickening and enhancement are clearly demonstrated with MRI and are most commonly seen in the radiocarpal joint (RCJ). Tenosynovitis can be seen in the wrist in more than half of patients presenting with RA. This most commonly involves the extensor carpi ulnaris tendon and is seen as sheath fluid, thickening and enhancement.     

Fetal central nervous system biometry on MR imaging

OBJECTIVE: We sought to compare the biometry of the fetal head on MR imaging with sonographic measurements in fetuses with and without suspected central nervous system abnormalities. MATERIALS AND METHODS: Blinded retrospective measurements of biparietal diameter, head circumference, and cerebellar width obtained on MR imaging were assigned a gestational age on the basis of median sonographic measurements and compared with sonographic and clinical assignment of gestational age in fetuses with no central nervous system abnormalities. In fetuses with central nervous system abnormalities, the same MR measurements were compared with sonographic measurements obtained within 1 week. Single-shot fast spin-echo sequences were obtained. Pearson's product moment correlation coefficients and paired sample t tests were performed. RESULTS: In 22 fetuses with no suspected central nervous system abnormalities, significant correlation was seen in the assignment of gestational age by MR measurements and sonographic gestational age. In 25 fetuses with central nervous system abnormalities, significant correlation was also seen between biparietal diameter and head circumference measurements. The mean biparietal diameter on MR imaging was greater than on sonography in those fetuses with central nervous system abnormalities (p = 0.038). CONCLUSION: MR imaging measurements of biparietal diameter, head circumference, and cerebellar width are strongly correlated to gestational age in fetuses without central nervous system abnormalities. Significant correlation is found between MR imaging and sonographic measurements of biparietal diameter and head circumference in fetuses with central nervous system abnormalities. Larger biparietal diameter measurements were seen with MR imaging than with sonography in the abnormal group. Fetal central nervous system biometry can be performed as part of the MR imaging evaluation of the fetal central nervous system.