Brain: gadolinium-enhanced fast fluid-attenuated inversion-recovery MR imaging

PURPOSE: To determine the clinical utility of gadolinium-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain by comparing results with those at gadolinium-enhanced T1-weighted MR imaging with magnetization transfer (MT) saturation. MATERIALS AND METHODS: In 105 consecutive patients referred for gadolinium-enhanced brain imaging, FLAIR and T1-weighted MR imaging with MT saturation were performed before and after administration of gadopentetate dimeglumine (0.1 mmol per kilogram of body weight). Pre- and postcontrast images were evaluated to determine the presence of abnormal contrast enhancement and whether enhancement was more conspicuous with the FLAIR or T1-weighted sequences. RESULTS: Thirty-nine studies showed intracranial contrast enhancement. Postcontrast T1-weighted images with MT saturation showed superior enhancement in 14 studies, whereas postcontrast fast FLAIR images showed superior enhancement in 15 studies. Four cases demonstrated approximately equal contrast enhancement with both sequences. Six cases showed some areas of enhancement better with T1-weighted imaging with MT saturation and other areas better with postcontrast fast FLAIR imaging. Superficial enhancement was typically better seen with postcontrast fast FLAIR imaging. CONCLUSION: Fast FLAIR images have noticeable T1 contrast making gadolinium-induced enhancement visible. Gadolinium enhancement in lesions that are hyperintense on precontrast FLAIR images, such as intraparenchymal tumors, may be better seen on T1-weighted images than on postcontrast fast FLAIR images. However, postcontrast fast FLAIR images may be useful for detecting superficial abnormalities, such as meningeal disease, because they do not demonstrate contrast enhancement of vessels with slow flow as do T1-weighted images.     

Application of turbo fluid-attenuated inversion-recovery MRI in evaluation of intraspinal tumors

PURPOSE: Although fluid-attenuated inversion-recovery (FLAIR) magnetic resonance imaging (MRI) is widely applied to diagnose central nervous system diseases, its role in diagnosis of intraspinal tumors is unclear. In this study, we evaluated the potential clinical application of a turbo FLAIR sequence for imaging of intraspinal tumors. MATERIALS AND METHODS: Forty-eight consecutive patients with intraspinal tumors underwent MRI with turbo FLAIR and turbo spinal echo (TSE) sequences. Turbo FLAIR images were then qualitatively and quantitatively compared with T2-weighted TSE images. RESULTS: Turbo FLAIR images were evaluated as superior to T2-weighted TSE images for image artifact, extradural tumor conspicuity, and intradural extramedullary tumor conspicuity and detection. Intramedullary tumor conspicuity with turbo FLAIR was less than T2-weighted TSE. Similar capabilities in detection of extradural and intramedullary tumors were found between turbo FLAIR and T2-weighted TSE. Turbo FLAIR and T2-weighted TSE displayed similar normal spinal cord signal-noise ratio (SNR) and tumor-to-cerebrospinal fluid (CSF) contrast-to-noise ratio (CNR). In addition, turbo FLAIR yielded significantly higher tumor-to-CSF contrast than T2-weighted TSE. However, tumor SNR, tumor-to-normal spinal cord contrast and CNR with turbo FLAIR images were lower than those with T2-weighted TSE images. CONCLUSION: This study demonstrated (a) a superiority of turbo FLAIR to T2-weighted TSE in displaying and detecting intradural extramedullary tumors, (b) a superiority of turbo FLAIR to T2-weighted TSE in demonstrating extradural tumors, and (c) less usefulness in displaying intramedullary tumors with turbo FLAIR than with T2-weighted TSE.     

Normal myelination of the pediatric brain imaged with fluid-attenuated inversion-recovery (FLAIR) MR imaging.

BACKGROUND AND PURPOSE: As in adult imaging, FLAIR can be applied to pediatric brain imaging, and this requires an appreciation of the normal pediatric brain appearance by FLAIR imaging. The purpose of this study was to describe the MR appearance of the brain in normal infants and young children as demonstrated by fluid-attenuated inversion-recovery (FLAIR) MR imaging. METHODS: We retrospectively examined MR brain studies, interpreted as normal by pediatric radiologists, from 29 patients (aged 1 to 42 months) to catalog the appearance of myelination in multiple brain areas. RESULTS: On T2-weighted images, white matter progressed from hyperintense to hypointense relative to adjacent gray matter over the first 2 years of life. An analogous, although slightly delayed sequence was observed on FLAIR images with the exception of the deep cerebral hemispheric white matter, which followed a triphasic sequence of development. On FLAIR images, the deep cerebral white matter was heterogeneously hypointense relative to gray matter in the young infant, became hyperintense early in the first few months of life, and then reverted to hypointense during the second year of life. CONCLUSION: The normal appearance and development of brain white matter must be taken into account when interpreting FLAIR images of infants and young children.     

Cerebral gliomas and metastases: assessment with contrast-enhanced fast fluid-attenuated inversion-recovery MR imaging

The effect of contrast material on fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance images was evaluated for 16 patients with enhancing gliomas and 12 patients with cerebral metastases. Because of a marked T1 effect, fast FLAIR imaging provided a marked contrast enhancement, resulting in the highest tumor-to-background contrast ratio compared with standard imaging techniques.     

Fast fluid-attenuated inversion-recovery MR of intracranial infections.

PURPOSETo assess the usefulness of fast fluid-attenuated inversion-recovery (FLAIR) MR sequences in the diagnosis of intracranial infectious diseases.METHODSWe compared fast FLAIR images with conventional spin-echo images (T1- and T2-weighted) obtained in 20 patients with infectious diseases (six with encephalitis, five with brain abscesses, three with meningitis, two with meningoencephalitis, two with Creutzfeldt-Jakob disease, one with epidural empyema, and one with cysticercosis). Two neuroradiologists independently reviewed the FLAIR images and compared them with the conventional spin-echo images, obtaining agreement in all patients.RESULTSFLAIR images of diagnostic quality were obtained in 18 patients. In two patients, FLAIR images were degraded by motion. Lesions in the patients with encephalitis and meningoencephalitis were better delineated on FLAIR images than on spin-echo images. FLAIR images clearly depicted lesions in the basal ganglia in both patients with Creutzfeldt-Jakob disease. In patients with brain abscess, meningitis, cysticercosis, and epidural empyema, FLAIR images provided no more information than conventional spin-echo images, and the lesions were seen better on postcontrast T1-weighted spin-echo images.CONCLUSIONFast FLAIR images showed pathologic changes in intracranial infectious diseases better than or as well as conventional T2- and proton density-weighted spin-echo sequences. However, postcontrast T1-weighted spin-echo sequences resulted in better visibility of abscess, meningitis, cysticercosis, and epidural empyema than did FLAIR images.     

Comparison of fluid-attenuated inversion-recovery MR imaging with CT in a simulated model of acute subarachnoid hemorrhage

BACKGROUND AND PURPOSE: Because MR imaging is becoming integral to the evaluation and treatment of very early stroke, it is critical to prove that MR imaging is at least as sensitive to acute subarachnoid hemorrhage (SAH) as is CT. The present study was conducted to evaluate the possibility of detecting a small amount of acute SAH diluted by CSF not revealed by CT but identified on fluid-attenuated inversion-recovery (FLAIR) MR images in an in vitro study. METHODS: Acute SAH was simulated with mixtures of artificial CSF and arterial blood (hematocrit [Hct], 45%) ranging from 0% to 100% by volume. We scanned these phantoms with CT and turbo-FLAIR MR imaging (9000/119 [TR/effective TE]; inversion time, 2200 ms; echo train length, 7), and we measured T1 and T2 relaxation times of these phantoms at temperatures within 36 degrees C to 37 degrees C. Plots of CT value from the different blood/water mixture ratios versus Hct were generated and correlated with the average CT value from normal cortex. We measured T1 and T2 relaxation times of these phantoms and normal cortex and generated T2 relaxation curves as a function of effective TE for a specific inversion time (2200), and determined the TR (9000) for the turbo-FLAIR sequence by using a theoretical equation for the turbo inversion recovery signal intensity. RESULTS: Above a Hct of 27% blood, the mixture was denser on CT scans than was the normal cortex. At a selected time longer than an effective TE of 120, above a Hct of 22.4% blood, the mixture was more hyperintense than the normal cortex on turbo-FLAIR images. At selected times longer than an effective TE of 160, above a Hct of 9% blood, the mixture was more hyperintense than was the normal cortex. CONCLUSION: FLAIR imaging is more sensitive than CT in the detection of a small amount of acute SAH diluted by CSF at selected appropriate TE, as determined in an in vitro study.     

Applicability and advantages of flow artifact-insensitive fluid-attenuated inversion-recovery MR sequences for imaging the posterior fossa

We describe a new sequence, flow artifact-insensitive fluid-attenuated inversion recovery (FAIS-FLAIR), that capitalizes on the advantages of fluid-attenuated inversion recovery (FLAIR) while minimizing FLAIR-related artifacts such as those often encountered in the posterior fossa. Twenty-eight patients with posterior fossa disease underwent FAIS-FLAIR, conventional FLAIR, and spin-echo MR studies, and the findings yielded by the three techniques were compared. In this patient population, postcontrast FAIS-FLAIR imaging was obtained in 20 patients and compared with postcontrast T1-weighted images. The images were assessed for lesion conspicuity by three radiologists. FAIS-FLAIR markedly reduces the inflow artifacts from noninverted CSF on FLAIR images. It does so with and without contrast agent administration, and produces higher lesion conspicuity compared with T1- and T2-weighted spin-echo sequences and conventional FLAIR images of the posterior fossa.     

Comparison of multishot echo-planar fluid-attenuated inversion-recovery imaging with fast spin-echo fluid-attenuated inversion-recovery and T2-weighted imaging in depiction of white matter lesions

PURPOSE: To compare a multishot echo-planar fluid-attenuated inversion-recovery (EPI-FLAIR) sequence with fast spin-echo FLAIR (F-FLAIR) and fast spin-echo T2-weighted (FSE-T2W) sequences in depiction of white matter lesions. METHODS: Thirty-five patients with various white matter lesions were included in this prospective study. Two independent readers for lesion detection (lesion size, >2 mm) compared sequences quantitatively. In 22 patients, contrast was calculated between periventricular hyperintensity (PVH) and the cerebrospinal fluid (CSF). RESULTS: EPI-FLAIR revealed more lesions than FSE-T2W (p < 0.01). However, F-FLAIR revealed more lesions than EPI-FLAIR (p < 0.01). For PVH-to-CSF contrast, EPI-FLAIR demonstrated significantly higher contrast than FSE-T2W. There were no differences in PVH-to-CSF contrast between EPI-FLAIR and F-FLAIR. CONCLUSIONS: This study shows that EPI-FLAIR has distinct advantages over FSE-T2W in the depiction of white matter lesions. Although EPI-FLAIR reduces imaging time by more than 60% relative to F-FLAIR, it cannot replace F-FLAIR for the detection of lesions in the cerebral white matter.     

液体衰减反转恢复序列MR成像在颅脑创伤诊断中价值的研究

目的评价MR液体衰减反转恢复序列(fluid-attenuated inversion recovery,FLAIR)诊断各种颅脑创伤病变的价值.方法22例颅脑创伤病例均进行了CT和MR T1WI、T2WI及FLAIR序列检查,CT与MR检查的时间间隔为4.6±3.7天.观察CT与三种MR序列上各种病变病灶的显示数,将FLAIR所见的结果分别与CT、T1WI及T2WI结果作统计学分析(t检验).结果22例共有100个颅内创伤病灶,CT检出率为25%,T1WI为49%,T2WI为71%,FLAIR检出率为100%,差异显著(P<0.0005).其中FLAIR对非出血性脑挫伤的显示效果最佳,优于其它三种技术(P<0.0005);对于出血性挫伤,FLAIR优于CT(P<0.0025),但与T1WI及T2WI无明显差别;FLAIR对硬膜下/硬膜外血肿的发现能力与其它三种技术相似,对硬膜下积液的显示优于CT(P<0.0025),与T1WI及T2WI则无显著差异;FLAIR对亚急性期的蛛网膜下腔出血(SAH)的显示能力超过CT和T2WI(P<0.05),但CT与FLAIR对急性SAH的显示能力一致.结论FLAIR序列能明显地改善颅脑创伤性病变的显示,优于CT和常规MRI技术,其中以非出血性挫伤和亚急性期的SAH效果最佳.FLAIR序列可作为颅脑创伤检查的常规手段.     

Accuracy for detection of simulated lesions: comparison of fluid-attenuated inversion-recovery, proton density--weighted, and T2-weighted synthetic brain MR imaging

OBJECTIVE: The objective of our study was to determine the effects of MR sequence (fluid-attenuated inversion-recovery [FLAIR], proton density--weighted, and T2-weighted) and of lesion location on sensitivity and specificity of lesion detection. MATERIALS AND METHODS: We generated FLAIR, proton density-weighted, and T2-weighted brain images with 3-mm lesions using published parameters for acute multiple sclerosis plaques. Each image contained from zero to five lesions that were distributed among cortical-subcortical, periventricular, and deep white matter regions; on either side; and anterior or posterior in position. We presented images of 540 lesions, distributed among 2592 image regions, to six neuroradiologists. We constructed a contingency table for image regions with lesions and another for image regions without lesions (normal). Each table included the following: the reviewer's number (1--6); the MR sequence; the side, position, and region of the lesion; and the reviewer's response (lesion present or absent [normal]). We performed chi-square and log-linear analyses. RESULTS: The FLAIR sequence yielded the highest true-positive rates (p < 0.001) and the highest true-negative rates (p < 0.001). Regions also differed in reviewers' true-positive rates (p < 0.001) and true-negative rates (p = 0.002). The true-positive rate model generated by log-linear analysis contained an additional sequence-location interaction. The true-negative rate model generated by log-linear analysis confirmed these associations, but no higher order interactions were added. CONCLUSION: We developed software with which we can generate brain images of a wide range of pulse sequences and that allows us to specify the location, size, shape, and intrinsic characteristics of simulated lesions. We found that the use of FLAIR sequences increases detection accuracy for cortical-subcortical and periventricular lesions over that associated with proton density- and T2-weighted sequences.     

CO中毒后迟发性帕金森症:应用反转恢复MR成像评价黑质

摘要目的应用灰质(GM)抑制反转恢复序列(IR)MRI定量研究CO中毒后迟发性帕金森症病人的黑质信号改变。材料与方法本前瞻性研究经当地伦理审查委员会批准且所有受试者均签署知情同意书。     

Abnormal hyperintensity within the subarachnoid space evaluated by fluid-attenuated inversion-recovery MR imaging: a spectrum of central nervous system diseases

A variety of central nervous system (CNS) diseases are associated with abnormal hyperintensity within the subarachnoid space (SAS) by fluid-attenuated inversion-recovery (FLAIR) MR imaging. Careful attention to the SAS can provide additional useful information that may not be available with conventional MR sequences. The purpose of this article is to provide a pictorial essay about CNS diseases and FLAIR images with abnormal hyperintensity within the SAS. We present several CNS diseases including subarachnoid hemorrhage, meningitis, leptomeningeal metastases, acute infarction, and severe arterial occlusive diseases such as moya-moya disease. We also review miscellaneous diseases or normal conditions that may exhibit cerebrospinal fluid hyperintensity on FLAIR images. Although the detection of abnormal hyperintensity suggests the underlying CNS diseases and narrows differential diagnoses, FLAIR imaging sometimes presents artifactual hyperintensity within the SAS that can cause the misinterpretation of normal SAS as pathologic conditions; therefore, radiologists should be familiar with such artifactual conditions as well as pathologic conditions shown as hyperintensity by FLAIR images. This knowledge is helpful in establishing the correct diagnosis.     

MR fluid-attenuated inversion recovery imaging as routine brain T2-weighted imaging

We tried to investigate if magnetic resonance (MR) fluid-attenuated inversion recovery (FLAIR) imaging can be used as a routine brain screening examination instead of spin-echo T2-weighted imaging. Three hundred and ninety-four patients with clinically suspected brain diseases were randomly selected and examined with both brain MR FLAIR and T2-weighted imaging on the axial plane. These two imaging techniques were evaluated by two neuroradiologists as to which imaging was better for routine brain T2-weighted imaging. In 123 of 394 cases (31%), FLAIR imaging was superior to spin-echo T2-weighted imaging. Especially in cases with inflammatory diseases, traumatic diseases and demyelinating diseases, FLAIR imaging was particularly useful. Small lesions bordering cerebrospinal fluid (CSF) are often detected only by FLAIR imaging. In 259 cases (66%), including 147 normal cases (37%), they were equally evaluated. Only in 12 cases (3%) was conventional T2-weighted imaging superior to FLAIR imaging. Cerebrovascular lesions like cerebral aneurysm and Moyamoya disease could not be detected on FLAIR images because these structures were obscured by a low signal from the CSF. Also, because old infarctions tend to appear as low signal intensity on FLAIR images, the condition was sometimes hard to detect. Finally, FLAIR imaging could be used as routine brain T2-weighted imaging instead of conventional spin-echo T2-weighted imaging if these vascular lesions were watched.     

Abnormal hyperintensity within the subarachnoid space evaluated by fluid-attenuated inversion-recovery MR imaging: a spectrum of central nervous system diseases

A variety of central nervous system (CNS) diseases are associated with abnormal hyperintensity within the subarachnoid space (SAS) by fluid-attenuated inversion-recovery (FLAIR) MR imaging. Careful attention to the SAS can provide additional useful information that may not be available with conventional MR sequences. The purpose of this article is to provide a pictorial essay about CNS diseases and FLAIR images with abnormal hyperintensity within the SAS. We present several CNS diseases including subarachnoid hemorrhage, meningitis, leptomeningeal metastases, acute infarction, and severe arterial occlusive diseases such as moyamoya disease. We also review miscellaneous diseases or normal conditions that may exhibit cerebrospinal fluid hyperintensity on FLAIR images. Although the detection of abnormal hyperintensity suggests the underlying CNS diseases and narrows differential diagnoses, FLAIR imaging sometimes presents artifactual hyperintensity within the SAS that can cause the misinterpretation of normal SAS as pathologic conditions; therefore, radiologists should be familiar with such artifactual conditions as well as pathologic conditions shown as hyperintensity by FLAIR images. This knowledge is helpful in establishing the correct diagnosis.

     

Fast fluid-attenuated inversion-recovery imaging: first experience with a 3D version in epilepsy

We developed a 3D version of fast fluid-attenuated inversion-recovery imaging (FLAIR) which provides images with a slice thickness of 1.5 mm. We present our initial experience with 3D fast FLAIR in patients with epilepsy. We compared 3D fast FLAIR (slice thickness 1.5 mm), 2D fast FLAIR (slice thickness 5 mm) and a 3D spoiled GRASS (IRSPGR) sequence (slice thickness 1.5 mm) in 10 patients with lesional epilepsy (head injury 1, hippocampal sclerosis 2, low-grade glioma 2, dysembryoplastic neuroepithelial tumour 2, polymicrogyria 1, perinatal infarct 1 and presumed thrombosed aneurysm 1). Both 2D and 3D fast FLAIR sequences yielded higher conspicuity for lesions than the T1-weighted IRSPGR sequence, except in the patient with polymicrogyria. The extent of the lesion, in particular that of low-grade tumours, was best assessed on 3D fast FLAIR images. 3D fast FLAIR may be a useful additional tool especially for imaging low-grade tumours. Received: 22 October 1997 Accepted: 16 December 1997     

Contrast optimization of fluid-attenuated inversion-recovery (FLAIR) MR imaging in patients with high CSF blood or protein content.

After surgical resection of a brain tumor or infection of the cerebrospinal fluid (CSF), elevated levels of blood by-products or protein contaminations are seen in the patient's CSF spaces. In fast fluid-attenuated inversion-recovery (FLAIR) imaging CSF signal is nulled by an appropriate choice of the inversion recovery time TI to improve the contrast between tissue structures adjacent to CSF-filled volumes. With contaminated CSF, however, the longitudinal relaxation time T(1) may change significantly, which results in an incomplete suppression in the FLAIR images, if standard inversion times are used. In this work, a fast single-voxel T(1) measurement pulse sequence with integrated T(1) calculation that allows determination the optimal TI value in 15 sec is presented. The method was tested in five patients after surgical resection of a brain tumor, where FLAIR MRI with and without contrast agent was performed to identify remaining tumor fragments at the margin of the resection cavity.     

Use of fluid-attenuated inversion-recovery pulse sequences for imaging the spinal cord.

Fourteen patients with disease of the spinal cord were imaged with fluid-attenuated inversion-recovery (FLAIR) sequences in which the inversion time was chosen to substantially reduce or null the signal from CSF. Lesions were seen with greater conspicuity than with conventional contrast-enhanced and -unenhanced T1- and T2-weighted sequences in 11 cases.     

MR of acute subarachnoid hemorrhage: a preliminary report of fluid-attenuated inversion-recovery pulse sequences.

We report preliminary results applying fluid-attenuated inversion-recovery (FLAIR) sequences to three patients with acute subarachnoid hemorrhage. Acute subarachnoid hemorrhage could be clearly demonstrated as areas of high signal intensity on FLAIR sequences in all patients. These preliminary results suggest that with FLAIR sequences one could reliably diagnose acute subarachnoid hemorrhage.