Magnetization transfer MR imaging in CNS tuberculosis.

BACKGROUND AND PURPOSE: CNS tuberculosis may simulate other granulomas and meningitis on MR images. The purpose of this study was to improve the characterization of lesions in CNS tuberculosis and to assess the disease load using magnetization transfer (MT) imaging. METHODS: A total of 107 tuberculomas in seven patients with or without meningitis and 15 patients with tuberculosis meningitis alone were studied. Fifteen patients with cysticercus granulomas with T2 hypointensity, five patients each with viral and pyogenic meningitis, and two patients with cryptococcal meningitis were also studied. The MT ratios were calculated from tuberculomas, cysticercus granulomas, and thickened meninges in tuberculous, viral, pyogenic, and cryptococcal meningitis and were compared within each pathologic group and with the MT ratio of different regions of normal brain parenchyma. Detectability of lesions on T1-weighted MT spin-echo (SE) images was compared with that on conventional SE and postcontrast MT-SE images. RESULTS: Thickened meninges appeared hyperintense relative to surrounding brain parenchyma in the basal and supratentorial cisterns on precontrast MT-SE images in all 18 patients with tuberculosis meningitis. These meninges were not seen or were barely visible on conventional SE images, and enhanced on postcontrast MT-SE images. The MT ratio from the thickened meninges of tuberculous meningitis was significantly lower than that from the meninges in cryptococcal and pyogenic disease and significantly higher than the meninges in viral meningoencephalitis. The MT ratio from T2 visible and invisible tuberculomas appeared to be significantly lower than that of normal white matter. The MT ratio of T2 hypointense cysticercus granuloma was significantly higher than that of T2 hypointense tuberculoma. CONCLUSION: Precontrast MT-SE imaging helps to better assess the disease load in CNS tuberculosis by improving the detectability of the lesions. With the use of MT ratios, it may be possible to differentiate tuberculosis from similar-appearing infective lesions on MR images.     

Magnetization transfer MR imaging correlation with histopathology in intracranial tuberculomas

OBJECTIVE: The purpose of this study was to correlate the differences in the magnetization transfer (MT) ratios of different components of the tuberculoma with histopathology and to see whether MT or conventional MR imaging correlates better with histopathology. METHODS: MT T1 and conventional spin echo MR imaging was performed in six patients with intracranial tuberculomas. The tuberculomas were excised as a single mass and ex vivo MR imaging was performed using the same protocol. The gross histopathology was compared with in vivo imaging with respect to the MR signal intensity (MT ratio) in all six specimens. RESULTS: The size of the tuberculomas was larger on MT T1-weighted images compared to T2-weighted images and matched the gross measurements of each specimen. The MT hyperintense rim matched the cellular component of the tuberculoma that was masked on T2-weighted images because of the associated perifocal oedema. The cellular component had a lower MT ratio compared to the necrotic components. CONCLUSION: The outer hyperintense rim and hyperintense strands are due to the cellular infiltrate, noncaseating granulomas, and gliosis while the hypointense core represents solid caseation. The cellular outer rim shows lower MT ratio compared to the core of the tuberculoma. Histological correlation of the cellular and necrotic components of tuberculomas is best shown with MT T1 imaging.     

Hepatic tumors: Magnetization transfer MR imaging with gadolinium enhancement

Thirty patients with 15 hepatocellular carcinomas, 10 metastases, four hemangiomas, and one cholangiocarcinoma underwent magnetic resonance imaging at 1.5 T with T1-weighted, T2- weighted spin-echo (SE) images, gradient-echo (GRE) magnetization transfer (MT) images, and gadolinium-enhanced T1-weighted SE and MT- GRE images. The MT effect and lesion-liver contrast-to-noise ratio (C/N) were calculated and visual assessment (qualitative analysis) performed for unenhanced and enhanced MT-GRE images and enhanced Tl-weighted SE images. The C/N values for hepatic adenocarcinomas (seven metastases and one cholangiocarcinoma) and hemangiomas were larger for enhanced MT-GRE images (adenocarcinoma, 8.4 ± 2.3 [P < 0.01); hemangioma, 24 ± 2.1 [P < 0.05]) than for enhanced GRE images (5.0 ± 1.9 and 18 ± 2.7, respectively). These enhancing tumors had the highest scores in the qualitative analysis. Enhanced MT-GRE images showed no advantage for depiction of hepatocellular carcinomas relative to the other images.     

Magnetization transfer contrast in MR imaging of the heart

The use of magnetization transfer contrast (MTC) in short-echo-time (TE) cardiac magnetic resonance (MR) imaging was evaluated. For most cardiac MR imaging protocols, either long TE and short repetition time or exogenous intravascular agents are used for generating contrast between the ventricular wall and cavity as well as detecting pathologic conditions of the ventricular wall. The major problem with long-TE images is that the motion of the heart degrades the spatial resolution of the image during the TE period. However, MTC is generated by an off-resonance irradiation during the interpulse delay period that is relatively insensitive to motion artifacts. Short-TE (5-15 msec) gradient-recalled echo sequences were used for imaging the heart with and without MTC. These studies revealed that MTC can be used to greatly improve the contrast between the myocardial wall and blood chamber in short-TE images and may provide useful parameters for tissue characterization in pathologic cardiac muscle.     

Magnetization transfer and diffusion tensor MR imaging of acute disseminated encephalomyelitis

BACKGROUND AND PURPOSE: Patients with acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS) have a similar pattern of abnormalities on conventional MR images. We used magnetization transfer and diffusion tensor MR imaging to quantify normal-appearing brain tissue and cervical cord disease in patients with ADEM and to compare findings with those in healthy volunteers and patients with MS. METHODS: Brain dual-echo, T1-weighted magnetization transfer, and diffusion tensor images were obtained in eight patients with ADEM, in 10 patients with MS, and in 10 healthy volunteers. Fast short-tau inversion recovery, T1-weighted, and magnetization transfer cervical cord images were also obtained. We identified lesions on the images and quantified their volumes. We performed histogram analysis of the magnetization transfer ratio (MTR) and average mean histogram analysis of the diffusivity (D) in normal-appearing brain tissue and MTR in the cervical cord. RESULTS: Histogram analysis of normal-appearing brain tissue in patients with MS showed significantly lower MTRs and peak positions and significantly higher D averages compared with those in patients with ADEM. Patients with MS had significantly lower MTRs and D peak heights and significantly higher average D compared with those in healthy volunteers. Between patients with ADEM and control subjects, normal-appearing brain tissue MTR and D histogram metrics did not differ significantly. Cervical cord MTRs did not differ between control subjects and patients with ADEM, whereas the average MTR and histogram peak position was significantly lower in patients with MS than in the other groups. CONCLUSION: Outside the acute phase of disease and as opposed to what happens in MS, the normal-appearing brain tissue and cervical cord in patients with ADEM are spared in the pathologic process.     

MR imaging in the presurgical workup of patients with drug-resistant epilepsy

BACKGROUND AND PURPOSE: Whether an epileptic lesion is detected with MR imaging depends on the quality of the images and the expertise of the reader. We analyzed the role of 1.5-T MR imaging in the presurgical evaluation of patients with drug-resistant epilepsy at one center. METHODS: In a 2-year prospective study, 385 patients with drug-resistant epilepsy underwent standardized MR imaging at 1.5 T. We analyzed whether lesions were detected, whether they were precisely characterized by MR imaging, and whether lesion characterization allowed us to estimate seizure outcomes. RESULTS: Lesions were found on MR images in 318 patients (83%). Following presurgical evaluation, 209 (66%) underwent surgery, and 109 (34%) did not. Freedom from seizures was achieved in 130 (70%) of 186 patients. Nine (14%) of 66 patients without an MR imaging lesion underwent surgery; histopathologic findings were unrevealing in seven patients, and five (56%) achieved freedom from seizures. Hippocampal sclerosis was the most common lesion (52%) and correctly characterized in 101 (97%) of 104 patients. Glioneuronal tumors (20%) were sometimes imprecisely characterized: Four nonenhancing gangliogliomas were mistaken for focal cortical dysplasias. Outcomes were not different between lesion groups. However, there were trends toward a favorable outcome for focal cortical dysplasias with balloon cells and an unfavorable outcome for gyral scars. CONCLUSION: MR imaging detection of lesions influences further presurgical workup, though lesion characterization does not allow us to predict seizure outcome. If MR imaging fails to depict a lesion and patients undergo surgery because of electrophysiologic findings, histopathologic findings are often unrevealing.     

Magnetization transfer imaging in patients with clinically isolated syndromes suggestive of multiple sclerosis

BACKGROUND AND PURPOSE: In patients with multiple sclerosis (MS), reduced magnetization transfer ratios (MTRs) have been reported in white matter that appears normal on studies obtained with conventional imaging techniques. The stage in the disease when this first becomes detectable is unclear. The purpose of this study was to measure the MTR of normal-appearing white matter (NAWM) and lesions in patients with clinically isolated syndromes (CIS), many of whom are at the earliest stages of MS, and to determine the prognostic value of any observed changes. METHODS: Twenty-seven CIS patients and 13 matched control subjects were studied. The mean MTR was measured from 10 regions of NAWM and, when present, from lesions. The patients were followed-up clinically for a median of 12 months. RESULTS: There was no significant difference in the mean MTR between NAWM in control subjects (38.5% units) and that in CIS patients (38.4% units). After 12 months' follow-up, MS developed in 26% of the patients. The MTR of NAWM in these patients did not differ from that of the other patients or the control subjects. CONCLUSION: The reduced MTR in NAWM, described in established MS, was not detectable in patients with CIS. MTR did not provide prognostic information for this short period of follow-up.     

Magnetization transfer ratio is unable to lateralize epileptic foci in patients with temporal lobe epilepsy

BACKGROUND AND PURPOSE: A preliminary report suggested that magnetization transfer ratio (MTR) was useful to lateralize epileptic foci in patients with refractory temporal lobe epilepsy (TLE). We attempted to confirm this finding in a larger group by investigating the relationship between MTR of mesial temporal structures and seizure lateralization in patients with refractory TLE. METHODS: We compared the MTR of amygdalae and hippocampi of 10 patients with unilateral TLE to values obtained from 10 healthy control participants. RESULTS: Three of 10 patients with TLE had MTR values that were 2 SD below the normal mean; the MTR abnormality was concordant with electroclinical lateralization in only one of the three. CONCLUSION: We conclude that MTR measurements of amygdalae and hippocampi are not useful for lateralization of TLE.     

创伤后应激障碍患者海马活体MR波谱研究

目的探讨创伤后应激障碍（PTSD）患者双侧海马活体MR波谱（MRS）的特点,为创伤后应激障碍的诊断和病因学机制提供线索.方法应用多体素活体MRS成像技术,对12例PTSD患者和12例正常对照者进行波谱分析,检测双侧海马的N-乙酰天门冬氨酸（NAA）,肌酸（Cr）和含胆碱化合物（Cho）峰值,并进行统计学比较.结果PTSD患者左侧海马的NAA/Cr比值明显低于正常对照组（F=9.99,P=0.006）,Cho/Cr比值差异无统计学意义（F=0.36,P=0.55）;右侧海马的NAA/Cr比值、Cho/Cr比值差异均无统计学意义（F=1.44,P=0.25）.性别之间的波谱差异比较无统计学意义（F=0.56,P=0.82）;年龄、受教育时间、PTSD症状严重程度与左侧海马NAA/Cr比值的相关系数分别为0.47、0.35和0.18,差异无统计学意义（P＞0.05）.结论PTSD患者左侧海马存在病理性变化,NAA/Cr比值低于正常人.     

Transneuronal degeneration in patients with temporal lobe epilepsy: evaluation by MR imaging

The aim of this study was to assess the MR imaging findings of transneuronal degeneration of limbic system in the patients with temporal lobe epilepsy, and to detect the influence of surgery on the anatomy of the limbic system. Axial and coronal T1- and T2-weighted MR images were retrospectively analyzed in 34 patients with temporal lobe epilepsy, focusing on transneuronal degeneration. In 17 of the 34 patients, MR images were also analyzed after selective amygdalo-hippocampectomy. Atrophy of the fornix, mamillary body, mamillothalamic tract (MTT), and thalamus ipsilateral to the epileptic focus was demonstrated on MR images in 14.7, 17.6, 8.8, and 11.8% of the 34 patients, respectively. Focal hyperintensity of the thalamus was found on T2-weighted images in 8.8% of the 34 patients. In 17 patients who were evaluated before and after surgery, transneuronal degeneration was seen more frequently after surgery: fornix (11.8 vs 29.4%), mamillary body (11.8 vs 52.9%), MTT (5.9 vs 11.8%), and thalamus (11.8 vs 11.8%). Transneuronal degeneration of the limbic system is clearly demonstrated by MR imaging in patients with temporal lobe epilepsy, and surgical intervention induces transneuronal degeneration more frequently.     

Functional connectivity MR imaging of the language network in patients with drug-resistant epilepsy

BACKGROUND AND PURPOSE:Subtle linguistic dysfunction and reorganization of the language network were described in patients with epilepsy, suggesting the occurrence of plasticity changes. We used resting state FC-MRI to investigate the effects induced by chronic epilepsy on the connectivity of the language-related brain regions and correlated it with language performance.MATERIALS AND METHODS:FC-MRI was evaluated in 22 right-handed patients with drug-resistant epilepsy (11 with LE and 11 with RE) and in 12 healthy volunteers. Neuropsychological assessment of verbal IQ was performed. Patients and controls underwent BOLD fMRI with a verb-generation task, and language function was lateralized by an LI. Intrinsic activity fluctuations for FC analysis were extracted from data collected during the task. Six seeding cortical regions for speech in both hemispheres were selected to obtain a measure of the connectivity pattern among the language networks.RESULTS:Patients with LE presented atypical language lateralization and an overall reduced connectivity of the language network with respect to controls. In patients with both LE and RE, the mean FC was significantly reduced within the left (dominant) hemisphere and between the 2 hemispheres. In patients with LE, there was a positive correlation between verbal IQ scores and the left intrahemispheric FC.CONCLUSIONS:In patients with intractable epilepsy, FC-MRI revealed an overall reduction and reorganization of the connectivity pattern within the language network. FC was reduced in the left hemisphere regardless of the epileptogenic focus side and was positively correlated with linguistic performance only in patients with LE.

MR imaging plays a crucial role in the preoperative assessment of patients with intractable epilepsy. Structural MR imaging is routinely used for the detection of epileptogenic brain lesions, whereas fMRI localizes brain functions on the cerebral cortex and establishes their spatial relationship with lesions. One of the most frequent applications of fMRI is presurgical mapping of language functions and identification of the dominant hemisphere for speech.^1,2Subtle linguistic dysfunction affects up to one-third of adults with chronic epilepsy,^3–5 even in the absence of a direct injury to the brain language network. Functional neuroimaging has demonstrated different patterns of activation and reorganization of the language network in patients with epilepsy compared with healthy subjects. Using fMRI, Brázdil et al⁶ described a different activation pattern of the Broca area in a group of patients with left mesial-temporal epilepsy. In addition, task-evoked BOLD activity within the language network was found to be less unbalanced toward the dominant hemisphere in patients with epilepsy, compared with the healthy controls, especially in patients with early seizure onset.² Taken as a whole, these results suggest the possibility that epilepsy may induce functional changes across remote cortical regions, including those specialized for speech.In addition to task-evoked fMRI studies, resting state FC-MRI can reveal the cortical connectivity among language-network regions by evaluating correlations of spontaneous BOLD signal-intensity fluctuations.^7–10 FC-MRI has attracted growing interest and new applications and can be reasonably considered a marker of neural connectivity.¹¹ Most important, FC-MRI seems particularly suited for clinical populations because subjects lie in the scanner without any imposed task, thus eliminating the need for complying with task instructions.¹² Similarly, FC analysis of intrinsic brain activity, typically performed on resting state data, can be performed on task-related data by subtracting the contribution of the BOLD activation response.^12,13Recently, Waites et al¹⁴ found a decreased resting state FC-MRI connectivity among language regions and an increased connectivity between the left inferior frontal gyrus and part of the DMN in a group of patients with left temporal lobe epilepsy compared with controls. These observations further confirm the influence of epilepsy on language-network activity and possibly account for subtle language impairments that may affect patients with epilepsy. However, we have little information about potential hemispheric differences in these patients; and most important, the changes in FC associated with verbal performance have not been studied previously, to our knowledge.In the present retrospective analysis, we investigated the FC pattern among language-network nodes in a group of patients (n = 22) with either left- or right-lateralized drug-resistant epilepsy and in a group of matched healthy subjects (n = 12). First, we evaluated the pattern of cortical activation during a conventional block-designed verb-generation task assessing the degree of language function lateralization across hemispheres. We then used FC-MRI to investigate the pattern of functional connectivity among 6 regions of the language network in the 2 hemispheres. Finally, we investigated the correlation between the pattern of FC-MRI and the neuropsychological evaluation of language performance.     

Magnetization transfer imaging diagnosis of intracranial tuberculomas

Tuberculomas (TB) can mimic brain tumors and abscesses. We performed prospective magnetization transfer ratio (MTR) analysis on 60 patients with 52 intracranial TB, 13 pyogenic abscesses and 65 tumors to determine the efficacy of magnetization transfer (MT) imaging in the differential diagnosis of brain tumors and infection. The nonenhancing cores of TB had significantly higher (P=.026) MTR (0.14+/-0.29) than necrotic components of high-grade gliomas (-0.19+/-0.22). The MTR of cores of TB were also higher than those of the cystic areas of low-grade gliomas (-0.53+/-0.32), benign (-0.09+/-0.21) and malignant (-0.07+/-0.25) tumors, and abscesses (-0.03+/-0.13), but the differences were not significant because of the small number of tumors and abscesses. There was also no significant difference between the MTR of abscesses, malignant and benign tumors. Using the criteria of MTR of necrotic center > 0.14 (mean MTR of TB) for diagnosing TB, MTR <-0.03 (mean MTR of abscesses) for diagnosing tumors and MTR between these values for diagnosing abscesses, MTI had diagnostic sensitivity of 68.42%, specificity of 80.49%, and accuracy of 76.67%. The improved diagnostic accuracy of MRI with the addition of MTR analysis from 86.67% to 91.67% and from 85.71% to 87.50% for both radiologists respectively was not significant. MTR analysis helped us to differentiate solitary TB or abscess from low-grade glioma in five patients and to diagnose multiple TB, abscesses, and metastases in four.     

Magnetization transfer imaging of traumatic brain injury

Magnetization transfer imaging (MTI) has been shown to be sensitive for the detection of white matter abnormalities in entities such as multiple sclerosis, progressive multifocal leukoencephalopathy, and wallerian degeneration. Our hypothesis was that MTI would detect traumatic white matter abnormalities (TWMA) and provide information additional to that obtainable with routine spin- and gradient-echo imaging. We hypothesized that the presence of TWMA defined by MTI would correlate with outcome following TBI. Twenty-eight victims of head trauma and 15 normal controls underwent magnetic resonance imaging including MTI. Magnetization transfer ratios (MTR) were calculated for areas of shearing injury and for normal-appearing white matter (NAWM) in locations frequently subject to diffuse axonal injury. Abnormal MTRs were detected in NAWM in eight patients. All eight had persistent neurologic deficits, including cognitive deficits, aphasia, and extremity weakness. Seven of the 28 patients had no abnormal findings on neurologic exam at discharge, transfer, or follow-up. None of these patients had an abnormal MTR in NAWM. In the remaining 13 patients, who had persistent neurologic deficits, no regions of abnormal MTR were detected in NAWM. MTI is a sensitive method for the detection of TWMA. Detection of abnormal MTR in NAWM that is prone to axonal injury may predict a poor patient outcome. The presence of normal MTR in NAWM in these areas does not necessarily confer a good outcome, however.     

Magnetization transfer contrast in fat-suppressed steady-state three-dimensional MR images.

We demonstrate that magnetization transfer contrast can be used to improve the diagnostic utility of fat-suppressed steady-state three-dimensional gradient-recalled images. Fat suppression is achieved using a "jump-return" pair of contiguous shaped pulses. No time interval exists between the pulses, and no RF echo is generated. The sequence normally produces images with "density" weighting. Preparation of the spin magnetization with off-resonance frequency-selective excitation creates magnetization transfer contrast which attenuates signal intensity in proportion to the exchange rate of magnetization from free water with magnetization from water bound to macromolecules or protons that have restricted mobility. The resulting images have excellent fat suppression with low sensitivity to motion since no subtraction is used. In addition, the mechanism of signal attenuation is independent of paramagnetic effects, and addition of Gd-DTPA produces signal enhancement from vascularized regions of tissue. Examples are presented for the knee and breast, where the observation of pathology with signal enhancement from Gd-DTPA is improved over conventional 3D fat-suppressed images.     

肝脏磁化传递对比MRI:无法区分健康的肝脏和肝硬化

目的使用磁化传递脉冲频率偏离波谱评估磁化传递对比MRI区分健康的肝脏和肝硬化的能力。材料与方法符合HIPAA法案的前瞻性研究已获机构审查委员会批准,并获得所有参与者的书面知情同意书,使用蛋白浓度在