Functional magnetic resonance imaging of the human lumbar spinal cord

PURPOSE: To determine whether consistent regions of activity could be observed in the lumbar spinal cord of single subjects with spin-echo functional MRI (fMRI) if several repeated experiments were performed within a single imaging session. MATERIALS AND METHODS: Repeated fMRI experiments of the human lumbar spinal cord were performed at 1.5 T with a single-shot spin-echo technique (half-Fourier single-shot turbo spin-echo (HASTE)) as used by previous investigators, and a modified method (fluid-attenuated inversion recovery (FLAIR)-HASTE) that nulled the otherwise highly variable signal from the cerebrospinal fluid (CSF). RESULTS: FLAIR-HASTE reduced the variability of the signal in the CSF region to background levels, and presumably reduced associated artifacts in the spinal cord. Consistent areas of activation in the spinal cord in response to a thermal stimulus just below the knee were not observed across the fMRI experiments with either method. CONCLUSION: FLAIR-HASTE was useful for removing artifact in the spinal cord signal induced by variability in the CSF signal. However, with the techniques used in this study, we were not able to confirm the presence of a consistent fMRI response in the lumbar spinal cord because of the signal enhancement by extravascular protons (SEEP) effect during thermal stimulation of the hindlimb.     

Relationship between contrast enhancement on fluid-attenuated inversion recovery MR sequences and signal intensity on T2-weighted MR images: visual evaluation of brain tumors

PURPOSE: To investigate the relationship between the degree of contrast enhancement in fluid-attenuated inversion recovery (FLAIR) sequences and tumor signal intensity on T2-weighted images. MATERIALS AND METHODS: A total of 96 patients suspected of having brain tumors were examined by MR imaging, and whenever a brain tumor with an enhancing part larger than the slice thickness was demonstrated on postcontrast T1-weighted images, postcontrast FLAIR images were additionally acquired. The tumor signal intensity on the T2-weighted images was visually classified as follows: equal or lower compared with normal cerebral cortex (group 1), higher than normal cortex (group 2), and as high as cerebrospinal fluid (CSF) (group 3). When a lesion contained several parts with different signal intensities on T2-weighted images, we assessed each part separately. In each group, we visually compared pre- and postcontrast FLAIR images and assessed whether tumor contrast enhancement was present. When contrast enhancement was present on FLAIR sequence, the degree of contrast enhancement in T1-weighted and FLAIR sequences was visually compared. RESULTS: Postcontrast T1-weighted images showed 46 enhancing lesions, including 48 parts, in 31 MR examinations. FLAIR images of the lesion-parts in group 1 (N=18) did not show significant contrast enhancement. In group 2 (N=12), all the parts were enhanced in FLAIR sequences, and three parts were enhanced more clearly in the FLAIR sequences than in the T1-weighted sequences. In group 3 (N=18), all the parts were enhanced equally or more clearly in the FLAIR sequences than in the T1-weighted sequences. CONCLUSION: The signal intensity in FLAIR sequences is largely influenced by both T1 and T2 relaxation time; there is a close relationship between the signal intensity of brain tumors on T2-weighted images and the degree of contrast enhancement on FLAIR sequences. When tumors have higher signal intensity than normal cortex on T2-weighted images, additional postcontrast FLAIR imaging may improve their depiction.     

Comparison of flow artifacts between 2D-FLAIR and 3D-FLAIR sequences at 3 T

It has been reported that 3D-FLAIR can reduce the flow artifact resulting from cerebrospinal fluid (CSF) at 1.5 T compared to 2D-FLAIR. Flow-related artifacts tend to be worse at 3 T than at 1.5 T. The purpose of this study was to compare the CSF flow artifacts of 2D-FLAIR and 3D-FLAIR sequences at 3 T in eight healthy volunteers. The grade of CSF-related artifacts were scored through observing the perimedullary cistern, cerebellopontine angle cisterns, fourth ventricule, prepontine cistern, suprasellar cistern, ambient cisterns, sylvian fissures, third ventricle and lateral ventricles. Grading was performed on either axial or sagittal images. The CSF in-flow artifact scores were significantly higher on axial 2D-FLAIR than on axial 3D-FLAIR MPR images in all areas except the bilateral sylvian fissures, and higher on sagittal 2D-FLAIR than on sagittal 3D-FLAIR MPR images in perimedullary, bilateral CP angle and suprasellar cisterns. The CSF-related flow artifacts were significantly reduced by 3D-FLAIR, while structures in the cistern were depicted more clearly, even at 3 T. Further study is necessary to compare the clinical efficacy between 2D-FLAIR and 3D-FLAIR in depicting subtle abnormalities.     

MRI findings in 32 consecutive lipomas using conventional and advanced sequences.

Intracranial lipomas are histologically benign and usually incidental magnetic resonance imaging findings that must be differentiated from ominous lesions. The authors describe 32 lipomas in 30 patients using conventional spin-echo (CSE) T1-weighted images (T1WI), CSE proton density (PDWI), CSE T2-weighted images (T2WI), fast spin-echo (FSE) T2WI, and FSE fluid-attenuated inversion recovery (FLAIR). Lipomas occurred most commonly in the trigonal choroid plexus, cerebral convexity, pericallosal, and quadrigeminal cistern regions. Lipomas were hyperintense on CSE T1WI and of variable appearance on CSE PDWI and CSE T2WI. Lipomas were isointense to hyperintense on FSE T2WI and hyperintense on FLAIR. Chemical shift artifact (CSA) usually was present on either CSE PDWI or CSE T2WI but was not seen on FSE images. One patient had intracranial hypotension associated with a large convexity lipoma. The authors conclude that lipomas appear different on CSE T2WI than on FSE T2WI. CSE PDWI and CSE T2WI are complementary in detecting CSA. The lack of CSA being detected in lipomas on FSE images most likely relates to inherent bandwidth differences compared with those of CSE. The hyperintense appearance of lipomas on FSE FLAIR and FSE T2WI may be confused with subacute hematomas. The authors recommend that if CSE technique by itself is used to exclude lipomas (in centers that are not using FSE), then T1WI, PDWI, and T2WI usually are sufficient. For centers using FSE routinely, fat saturation or CSE sequences also may be needed to exclude lipomas. Finally, the authors' series suggests that intracranial lipomas may occur in lateral locations more frequently than reported previously.     

磁共振弥散成像在急性脑梗死诊断中的应用

目的 探讨磁共振（MR）弥散成像在急性脑梗死的诊断价值。方法 分析48例起病3天内急性脑梗死患者的MR-DWI表现,与常规T1WI、T2WI、FLAIR对照统计分析。结果 急性脑梗死在DWI表现为高信号,本组急性梗死灶在DWI显示达100％,高于T1WI（52．1％）、T2WI（60．4％）、FLAIR（79．2％）,差异有统计意义;MR不同序列扫描显示病灶的最早时间分别是T1WI7小时、T2WI7小时、DWI4小时、FLAIR6小时。结论 DWI可以早期明确诊断急性,尤其是超急性期脑梗死,与T2WI及FLAIR压水像相结合,有利于鉴别新旧梗死。     

MRI的FLAIR和SET2WI序列对急性脑梗死诊断的对比研究

目的研究MRI诊断脑梗死FLAIR序列和常规SET2WI序列的临床应用价值。方法对51例经常规MRI诊断为脑梗死的患者进行FLAIR序列成像，并与SE序列T2加权像比较。结果SET2WI显示急性脑梗死病灶105个，FLAIR显示急性脑梗死病灶110个病灶，有2个脑干部位病灶仅为SET2WI显示，而SET2WI显示的腔隙性病灶经FLAIR序列显示其中有10个为低信号，考虑为血管周围间隙，7个为低信号件周围高信号，考虑为陈旧性脑梗死灶，未予计算在内。结论急性脑梗死诊断中FLAIR序列成像与SET2WI序列互为补充，应作为常规序列使用。     

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 multi-reader 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.     

FLAIR和DWI在急性脑梗死的诊断中的应用

目的 评价液体衰减反转恢复（FLAIR）序列和弥散加权成像（DWI）在急性脑梗塞中的作用。方法 130例急性脑梗塞患者接受FLAIR和DWIMR检查,评价病变的显示程度。结果 FLAIR序列和DWI对病变的显示范围、对比均优于常规T2WI,以DWI对病变显示更佳。结论 FLAIR和DWI在急性脑梗塞中均有用,以DWI最好。     

T2-FLAIR序列在显示颅内脑膜瘤"脑膜尾征"中的价值

目的探讨T2-FLAIR序列在显示颅内脑膜瘤“脑膜尾征”中的价值。方法回顾性分析45例手术病理证实的颅内脑膜瘤T2-FLAIR与T1WI增强扫描显示“脑膜尾征”情况。结果T2-FLAIR序列与T1WI增强扫描均显示29例存在“脑膜尾往”，“脑膜尾征”在T2-FLAIR与T1WI增强扫描均表现为邻近肿瘤的脑膜增厚，呈单尾、双尾或三尾；在T2-FLAIR序列为略高信号，T1WI增强扫描为明显高信号。结论T2-FLAIR序列在显示脑膜瘤“脏膜尾征”有重要价值，对亍怀疑脑膜瘤而不行增强扫描患者其应作为常规扫描序列，以利于提高诊断的准确率。     

MRI之FLAIR技术在诊断脑室型囊虫病的应用价值

目的评价液体衰减反转恢复(FLAIR)序列对脑室型囊虫病的应用价值.方法对1997-06～2000-06期间经0.5T超导型MR设备检查诊断为脑室型囊虫病有手术和病理结果者18例(手术证实16例,2例误诊)进行分析,并比较应用FLAIR序列与常规自旋回波(SE)序列的成像效果.结果本组病例中,FLAIR序列检出脑室内囊虫23个,常规SE序列检出12个(为FLAIR序列的52.2%),前者敏感性高.室内囊虫之内部结构与边缘情况亦以FLAIR序列显示为好.结论FLAIR序列用来抑制脑脊液自由水的信号,可进一步发现和明确在常规SE序列成像上未能见到的或可疑的室内病灶,故为常规SE序列检查的重要补充.本文就误诊原因进行讨论.