Fast Fast Fluid-attenuated Inversion Recovery Research Articles

Usefulness of contrast-enhanced FLAIR MRI in the diagnosis of intracranial tumors

目的 评价增强后液体衰减反转恢复序列(FLAIR)在颅内肿瘤诊断中的应用价值.方法 104例颅内肿瘤,经手术、病理证实共有病灶124个.分别行增强前、后T1WI和FLAIR扫描.由2名有经验的放射科医生对所有病例进行评价.评价内容包括:增强例数、增强病灶个数及强化病灶部位;对比度及增强率;病变大小和范围.结果行统计学分析.结果 104例中,增强后FLAIR(CE FLAIR)成像、增强SE T1WI(CE T1WI)均显示98例有强化.CE FLAIR成像检出了117个强化灶,CE T1WI检出了120个.4个病灶仅在CE FLAIR显示而CE T1WI未显示.另有7个病灶仅在CE T1WI显示而CE FLAIR未显示.两者之信噪比(SNR)差异无统计学意义(t=1.10,P=0.270),脑灰白质对比度(GMC)、对比噪声比(CNR)及强化率(CER)差异均有统计学意义(t值分别为2.46、7.10、9.67,P值分别为0.015、0.000、0.000).在显示病灶大小上,CE FLAIR成像明显大于CE T1WI(t=4.13,P=0.000),在病灶范围上,有62例 CE FLAIR成像较CE T1WI大.CE FLAIR成像对位于脑沟、凸面、侧脑室旁及侧脑室内病灶的检出优于CE T1WI,而对大脑半球及第四脑室内的病灶的显示不如CE T1WI.结论 CE FLAIR成像与CE T1WI比较,强化病灶数,两者无明显差别,强化程度CE T1WI明显高于CE FLAIR成像,但两者对不同部位病灶的显示有明显差异,CE FLAIR成像显示病灶大小和范围明显大于CE T1WI.两种序列相互补充,建议将CE FLAIR成像序列列为增强后常规序列。

Rim enhancement of meningiomas on fast FLAIR imaging.

We investigated the enhancement patterns of meningiomas on fast fluid-attenuated inversion-recovery (FLAIR) images and related them to the size and histology of the tumour and the associated oedema. We studied 30 meningiomas with T2-weighted fast spin-echo (SE) images plus T1-weighted SE images with magnetisation-transfer saturation and fast FLAIR before and after contrast enhancement at 0.5 tesla. There were 21 meningiomas (70%) which showed peripheral (rim) enhancement on fast FLAIR, while only one, which showed heavy central calcification, enhanced peripherally on the SE images. Of the meningiomas with capsular enhancement on fast FLAIR 20 (95%) were more than 2 cm in diameter. The nine 9 smaller meningiomas enhanced homogeneously. This difference was statistically significant pattern ( P<0.01). All meningiomas which had associated oedema showed the capsular pattern although their number (6; 20%) was to small to analyse statistically. Only 11 (36%) tumours were examined histologically; peripheral enhancement was observed in all types of meningioma. This pattern may help to differentiate meningiomas from other extra-axial masses.

Isotropic 3D fast FLAIR imaging of the brain in multiple sclerosis patients: initial experience

The application of image registration and subtraction to detect change in multiple sclerosis (MS) disease burden on serial MR scans benefits from the use of isotropic voxels. An optimised 3D fast fluid-attenuated inversion recovery (FLAIR) sequence with 1.2- and 1.8-mm cubic voxels was compared with a 2D T2 SE sequence using standard 3-mm slices. Three-dimensional fast FLAIR and T2 SE series were obtained in 20 MS patients and 15 controls. Whole brain acquisition times for the 1.2- and 1.8-mm FLAIR were 21 and 10.5 min, respectively, for the interleaved T2 SE 16 min. Brain lesions were marked in consensus by two radiologists and the CNR was calculated in ten lesions. The mean number of lesions detected with the 1.2-mm FLAIR sequence was 115 +/- 76, compared with 85 +/- 59 for the T2 SE series ( p<0.001). The 1.8-mm FLAIR detected only 73 +/- 46 lesions. The CNR of the 1.2-mm FLAIR was significantly better than the T2 SE ( p<0.01), but not as good as the 1.8-mm FLAIR. In conclusion, isotropic 3D fast FLAIR using 1.2-mm cubic voxels is superior to the 2D T2 SE in the detection of brain lesions in MS patients. The isotropic 1.8-mm FLAIR is faster and has better contrast characteristics but lacks sensitivity.

Assessment of cerebral gliomas by a new dark fluid sequence, high intensity REduction (HIRE): a preliminary study.

The purpose of this study was to assess the diagnostic potential of a new dark fluid sequence, high intensity reduction (HIRE) in the diagnostic workup of patients with cerebral gliomas. The HIRE sequence utilizes a very long T(2) value of the cerebrospinal fluid (CSF) to suppress its high signal contribution in T(2)-weighted imaging by a image subtraction technique. Fifteen patients with histologically confirmed cerebral gliomas were examined with T(2)-weighted fast spin-echo (FSE), T(1)-weighted SE, fast fluid-attenuated inversion recovery (FLAIR), and HIRE imaging using identical scan parameters. In patients with enhancing lesions, fast FLAIR and HIRE were added to the contrast-enhanced T(1)-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative analysis, lesion detection, lesion delineation, and differentiation between enhancing and non-enhancing tumor tissue were assessed in a two-reader study. For the quantitative analysis, lesion-to-background and lesion-to-CSF contrast and contrast-to-noise ratios were determined in a region of interest analysis. HIRE achieved a significant reduction of the CSF signal without losing the high gray-to-white matter contrast of T(2)-weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE images were lower compared with the FLAIR images due to a relatively high background and CSF signal. After administration of contrast media, HIRE images presented a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared with T(2)-weighted FSE, the tumor delineation with HIRE was better in nine patients, equal in four patients, and less in one patient. Compared with the FLAIR images, HIRE was rated superior in three patients, equal in nine patients, and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images had significantly fewer image artifacts than FLAIR images due to reduced inflow effects. The T(2)-based HIRE sequence presented is an alternative to the T(1)-based FLAIR sequence, with the advantage of better gray-to-white matter contrast and shorter measurement time. Due to the subtraction technique, signal intensities from tissues with relaxation times in the range T(2 WM) < < T(2) < T(2 CSF) are also gradually affected, corresponding to their T(2) values. With respect to this unwanted effect, an improvement in HIRE imaging will be possible by using a self-weighted subtraction algorithm. In a forthcoming study this concept will first be tested on appropriate phantom fluids.

The sensitivity of thin-slice fast spin echo, fast FLAIR and gadolinium-enhanced T1-weighted MRI sequences in detecting new lesion activity in multiple sclerosis.

Fast fluid-attenuated inversion-recovery (FLAIR) and proton density/T2-weighted fast spin echo (FSE) brain images with 3-mm slices were acquired monthly for 7 months in 37 multiple sclerosis patients. New and enlarging lesions were counted and compared according to the site of lesions seen with each sequence. In addition, the number of new enhancing lesions seen on gadolinium-enhanced T1-weighted brain magnetic resonance imaging at the same time points was counted. All sequences used 3-mm contiguous axial slices. Overall, 126 new or enlarging lesions were seen on FSE and 135 on fast FLAIR (P = 0.25, Wilcoxon signed ranks test). Regional comparisons revealed significantly more fast FLAIR lesions only in the cortical/subcortical areas. There was a total of 295 new enhancing lesions over the same period -- a gain in the number of 'active lesions' of 234% seen with FSE and 218% with FLAIR. It is concluded that serial thin slice fast FLAIR is only slightly superior to FSE in detecting new and enlarging multiple sclerosis lesions but the difference is not sufficient to recommend that FLAIR should replace FSE in short-term, exploratory trials in MS using monthly scanning. Gadolinium-enhanced imaging is more then twice as sensitive as either FSE or fast FLAIR to new multiple sclerosis lesion activity, and enhancing lesions should provide the primary outcome measure in such studies.

Fast Fluid-Attenuated Inversion-Recovery MR of Intracranial Infections

PURPOSE To assess the usefulness of fast fluid-attenuated inversion-recovery (FLAIR) MR sequences in the diagnosis of intracranial infectious diseases. METHODS We 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. RESULTS FLAIR 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. CONCLUSION Fast 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.

Yield of Fluid-Attenuated Inversion Recovery in Drug-Resistant Focal Epilepsy with Noninformative Conventional Magnetic Resonance Imaging

Purpose: To determine the role in presurgical assessment and evaluate the yield of fast fluid-attenuated inversion recovery (FLAIR) sequences for patients with intractable partial epilepsy for whom conventional magnetic resonance imaging (MRI) was normal. Material and Methods: Forty patients were selected. Conventional MRI including spin echo T₁-weighted sagittal images and fast spin echo T₂-weighted axial images was normal in 33 patients and showed noninformative lesions in 7. Fast FLAIR and T₂-weighted sequences were performed perpendicularly to the hippocampal long axis. Results: Additional abnormalities were found in 40%. They were correlated with electroclinical data in 13 patients (32.5%) and not correlated or doubtful in 3 (7.5%). Conclusion: Fast FLAIR sequences brought congruent additional information in 32.5% cases and seemed useful in presurgical evaluation.

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.

Hyperacute Middle Cerebral Artery Territory Infarction: Comparison of Unenhanced CT, Spin-Echo T2-weighted,Fast FLAIR, and Diffusion-weighted MR Imaging

Purpose : To compare the detection rate of unenhanced CT, spin-echo T2-weighted, fast fluid-attenuatedin-version- recovery(FLAIR), and diffusion-weighted MR imaging in the diagnosis of hyperacute middle cerebralartery(MCA) territory infarction. Materials and Methods : Sixteen patients with clinically proven hyperacute MCAterritory infarction were e-valuated with unenhanced CT and MR. All CT examinations were performed within sixhours of the onset of symptoms and all MR studies were performed within two hours of CT. All images were evaluatedindepen-dently by two radiologists in possession of brief clinical information. Positive imaging criteria wereparenchy-mal hypoattenuation, as seen on CT, and increased signal intensity, as seen on MR. For quantitativeanalysis, we measured the attenuation and signal intensity of the lesion and contralateral normal parenchyma, andper-centage contrast-to-noise ratios(CNRs) of the lesions were also calculated . Results : Positive findings weredetected in all patients on diffusion-weighted images, in 13(81%) on CT, in 10 ( 63 %) on fast FLAIR images, andin 7(44 %) on T2-weighted images. Lesion percentage CNRs were 30% for diffusion-weighted imaging, 15 % for CT, 18% for FLAIR MR imaging, and 16 % for T2-weighted MR imag-ing(p

Subcallosal striations: early findings of multiple sclerosis on sagittal, thin-section, fast FLAIR MR images.

To determine how sensitive and specific the magnetic resonance (MR) imaging finding of subcallosal striations is for multiple sclerosis (MS). In 18 patients with clinically suspected MS and 32 age-matched patients without MS, sagittal 2-mm fast fluid-attenuated inversion-recovery (FLAIR) imaging was added to the routine MR studies of the brain. The images were reviewed for the presence of subcallosal striations, that is, linear, 1-mm-thick foci of hyperintensity perpendicular to the ependyma, like a stack of coins. The images were masked to exclude the hemispheric white matter and were interpreted without knowledge of patient age or medical history. Seventeen patients with clinical MS had subcallosal striations; one did not. Of the 32 patients without MS, five had subcallosal striations and 27 did not. Subcallosal striations were highly associated (P < .001) with clinical MS. Subcallosal striations are thought to represent perivenular demyelination, that is, the same process that later produces the "ovoid" lesions visible on routine MR images. Subcallosal striations are not seen on routine axial MR images and can be seen only on 2-mm sagittal FLAIR images.

MR imaging of the hippocampus: measurement of T2 with four dual-echo techniques.

To assess the effect of cerebrospinal fluid (CSF) signal nulling and different magnetic resonance (MR) imaging read-out implementations on the precision of T2 measurements in the hippocampus. Oblique coronal MR imaging was performed in 12 healthy volunteers by using four dual-echo MR sequences: conventional spin-echo (SE), fast SE, gradient-echo and SE (GRASE), and fast fluid-attenuated inversion-recovery (FLAIR) imaging. T2 measurements were obtained from T2 maps derived from regions of interest within the head of both hippocampi. T2 measurements obtained with the four MR sequences were compared, as were differences in T2 between right and left hippocampi. Interrater and test-retest consistency were determined. Fast FLAIR imaging provided the smallest normal range and SD of T2 measurements. Fast FLAIR and fast SE imaging provided the smallest coefficients of variation. GRASE imaging provided a lower coefficient of variation than that of conventional SE. The mean difference between left and right hippocampi was smallest at fast FLAIR imaging. Use of a CSF-nulling inversion prepulse, fast SE read-out, or GRASE read-out MR sequence helps improve the precision of the hippocampal T2 measurements in comparison with use of conventional SE imaging. T2 measurements obtained at dual-echo fast FLAIR imaging may help detect subtle hippocampal abnormalities.

Fast fluid-attenuated inversion-recovery (FLAIR) MRI in the assessment of intraaxial brain tumors.

This study demonstrates the value of a fast fluid-attenuated inversion-recovery (FLAIR) technique in the assessment of primary intraaxial brain tumors. Twenty-one patients with primary intraaxial brain tumors were examined by T2-weighted, proton-density-weighted fast spin echo, fast FLAIR, and contrast-enhanced T1-weighted spin echo using identical slice parameters. The images were evaluated using quantitative and qualitative criteria. Quantitative criteria were tumor-to-background and tumor-to-cerebrospinal fluid (CSF) contrast and contrast-to-noise ratio (CNR). The qualitative evaluation was performed as a multireader analysis concerning lesion detection, lesion delineation, and image artifacts. In the qualitative evaluation, all readers found the fast FLAIR to be superior to fast spin echo in the exact delineation of intraaxial brain tumors (P < .001) and the delineation of enhancing and nonenhancing tumor parts. Fast FLAIR was superior in the delineation of cortically located and small lesions but was limited in lesions adjacent to the ventricles. Fast FLAIR provided a significantly better tumor-to-CSF contrast and tumor-to-CSF CNR (P < .001). The tumor-to-background contrast and tumor-to-background CNR of the fast FLAIR images were lower than those of T2-weighted spin-echo images but higher than those of proton-density-weighted spin-echo images. FLAIR images had more image artifacts influencing the image interpretation in only two patients. Signal hyperintensities at the ventricular border were present in 92% of the patients. They are common findings in fast FLAIR and should be included into the image interpretation.

Fast flair imaging of the brain using the fast spin-echo and gradient spin-echo technique

The purpose of this study was to compare the gradient spin-echo (GRASE) to the fast spin-echo (FSE) implementation of fast fluid-attenuated inversion recovery (FLAIR) sequences for brain imaging. Thirty patients with high signal intensity lesions on T 2-weighted images were examined on a 1.5 T MR system. Scan time-minimized thin-section FLAIR-FSE and FLAIR-GRASE sequences were obtained and compared side by side. Image assessment criteria were lesion conspicuity, contrast between different types of normal tissue, image quality, and artifacts. In addition, contrast ratios and contrast-to-noise ratios were determined. Compared to FSE, the GRASE technique allowed a 17% reduction in scan time but conspicuity of small lesions in particular was significantly lower on FLAIR-GRASE images because of higher image noise and increased artifacts. Gray-white differentiation was slightly worse on FLAIR-GRASE. Physiological ferritin deposition appeared slightly darker on FLAIR-GRASE images and susceptibility artifacts were stronger. Fatty tissue was less bright with FLAIR-GRASE. With current standard hardware equipment, the GRASE technique is not an adequate alternative to FSE for the implementation of fast FLAIR sequences in routine clinical MR brain imaging.

Suspected multiple sclerosis: MR imaging with a thin-section fast FLAIR pulse sequence.

To compare thin-section, sagittal, fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging with conventional axial spin-echo (SE) imaging for early detection of multiple sclerosis (MS) in the brain. Conventional 5-mm axial proton-density- and T2-weighted SE images and sagittal 2-mm fast FLAIR images of the brain in five healthy volunteers and 25 patients with clinically suspected MS were evaluated and graded as normal or as showing possible or probable MS in a double-blind study. Fast FLAIR was judged better than SE in 37% of cases, equal to SE in 63%, and never worse than SE. In 43% of patients considered to have normal SE images, fast FLAIR images showed abnormalities consistent with MS. A subependymal striated appearance observed in several cases is believed to represent early inflammation and/or demyelination around subependymal veins in MS. Sagittal thin-section fast FLAIR is superior to conventional axial proton-density- and T2-weighted SE pulse sequences for detection of MS plaques in the brain.

Initial clinical experience in MR imaging of the brain with a fast fluid-attenuated inversion-recovery pulse sequence.

To evaluate fast fluid-attenuated inversion-recovery (FLAIR) technique for imaging brain abnormalities. A fast FLAIR sequence was developed that provided 36 5-mm contiguous sections in 5 minutes 8 seconds. Resulting images were compared with dual-echo T2-weighted spin-echo images of 41 consecutive patients with brain abnormalities. Contrast and contrast-to-noise ratios (C/Ns) (for contrast between the lesion and background and between the lesion and cerebrospinal fluid) for fast FLAIR exceeded the corresponding values for T2-weighted spin-echo images for all but the second-echo lesion-to-background C/N. Fast FLAIR provided equivalent or greater overall lesion conspicuity and enabled greater lesion detection in 98% and 100%, respectively, of the evaluations. Fast FLAIR images more often had image artifact, but this did not interfere with image interpretation in a significantly (P < or = .05) greater number of evaluations. Fast FLAIR provides images that are superior to proton-density- and T2-weighted images for many image quality criteria.