Patterns of lesion development in multiple sclerosis: longitudinal observations with T1-weighted spin-echo and magnetization transfer MR.

PURPOSEWe evaluated the appearance of enhancing multiple sclerosis (MS) lesions on unenhanced T1-weighted MR images and the natural course of enhancing MS lesions on serial unenhanced T1-weighted and magnetization transfer (MT) MR images.METHODSOne hundred twenty-six enhancing lesions were followed up monthly for 6 to 12 months to determine their signal intensity on unenhanced T1-weighted and MT MR images. At the time of initial enhancement, the size of the lesion and the contrast ratio of enhancement were calculated for each enhancing lesion. During follow-up, the contrast ratio on the corresponding unenhanced T1-weighted image was measured, and an MT ratio (MTR) was calculated.RESULTSTwenty-five enhancing lesions (20%) appeared isointense and 101 lesions (80%) appeared hypointense relative to normal-appearing white matter on unenhanced T1-weighted images. During 6 months of follow-up, four MR patterns of active lesions were detected: initially isointense lesions remained isointense (15%); initially isointense lesions became hypointense (5%, most of which reenhanced); initially hypointense lesions became isointense (44%); and initially hypointense lesions remained hypointense (36%). MTR was significantly lower for hypointense lesions as compared with isointense lesions at the time of initial enhancement. For lesions that changed from hypointense to isointense, MTR increased significantly during 6 months of follow-up. Multiple regression analysis showed that strongly decreased MTR at the time of initial enhancement and enhancement duration of more than one scan were predictive of a hypointense appearance on unenhanced T1-weighted images at 6 months'' follow-up. Ring enhancement was found to be the only (weak) predictor of persistently hypointense signal intensity.CONCLUSIONMost enhancing lesions appear slightly to significantly hypointense on unenhanced T1-weighted images. Although most hypointensities are reversible, only those lesions that fail to recover on unenhanced T1-weighted and MT images may have considerable irreversible structural changes.     

Characterization of multiple sclerosis plaques with T1-weighted MR and quantitative magnetization transfer.

PURPOSETo investigate the relationship between the appearance of multiple sclerosis lesions identified on unenhanced T1-weighted images and their corresponding magnetization transfer ratios.METHODSA total of 119 white matter lesions seen on T2-weighted images in 17 patients with multiple sclerosis were evaluated. Axial T1-weighted images were used to classify the lesions as isointense to white matter (10 lesions), hypointense to white matter but hyperintense to gray matter (44 lesions), hypointense to gray matter (59 lesions), and relatively isointense to cerebrospinal fluid (6 lesions). The magnetization transfer ratio of each lesion was calculated, and an average magnetization transfer ratio for each subcategory was determined.RESULTSThe magnetization transfer ratio values became progressively lower with increasing hypointensity of lesions on T1-weighted images. The average magnetization transfer ratio for lesions isointense to white matter, hypointense to white matter but hyperintense to gray matter, hypointense to gray matter, and relatively isointense to cerebrospinal fluid was 34.90 +/- 2.67 mean +/- SD), 30.93 +/- 3.57, 27.27 +/- 3.56, and 23.62 +/- 2.83, respectively. All groups were significantly different from each other.CONCLUSIONLesions isointense to white matter exhibited higher magnetization transfer ratio values than lesions that were hypointense. These findings are consistent with relative preservation of the myelin structure in the former, perhaps indicating that these lesions are predominantly inflammatory (edematous) in nature. The proportionately lower magnetization transfer ratio values of lesions that appear progressively more hypointense on T1-weighted images may reflect varying degrees of demyelination, with increasing lesion hypointensity corresponding to more breakdown in the macromolecular structure. These results suggest that T1-weighted images may be useful in characterizing the underlying pathologic substrate in multiple sclerosis plaques.     

Lysolecithin-induced demyelination in primates: preliminary in vivo study with MR and magnetization transfer.

PURPOSETo study bystander demyelination in multiple sclerosis with an experimental in vivo model of toxic demyelination.METHODSToxic demyelinating lesions were created in two monkeys by injection of lysophosphatidylcholine in the centrum semiovale. Follow-up was done clinically and with serial MR studies, including T2-weighted and gadolinium-enhanced T1-weighted images and measurement of magnetization transfer ratio, until the animals were killed at days 14 and 34, respectively. Light and electron microscopy analysis was compared with MR data.RESULTSInterval measurement of magnetization transfer ratio during the course of the experiment revealed a maximum decrease at day 7 to day 8, associated with the greatest clinical manifestations. The lowest values of magnetization transfer ratio correlated with histopathologic findings of myelin and axon destruction. Magnetization transfer ratio measurements appear to be sensitive to macromolecular destruction and specifically to membrane disorganization. At no time was gadolinium enhancement observed in this model of toxic demyelination.CONCLUSIONPreliminary results of this study indicated that magnetization transfer is a good technique to follow in vivo matrix destruction in brain parenchyma lesions. The results suggest also that phases of toxic demyelination in multiple sclerosis might not show gadolinium enhancement. Differentiation between demyelinating activity and associated inflammation in multiple sclerosis lesions should be considered in further in vivo work.     

Quantitative diffusion measurements in focal multiple sclerosis lesions: correlations with appearance on TI-weighted MR images

OBJECTIVE: Relative hypointensity on T1-weighted MR imaging has been suggested as a putative disability marker. The purpose of our study was to determine if there are quantifiable diffusion differences among focal multiple sclerosis lesions that appear differently on conventional T1-weighted MR images. We hypothesized that markedly hypointense lesions on unenhanced T1-weighted images would have significantly increased diffusion compared with other lesions, and enhancing portions of lesions would have different diffusion compared with nonenhancing lesions. SUBJECTS AND METHODS: Average apparent diffusion coefficient (ADC) was calculated for 107 lesions identified on T2-weighted images in 16 patients with multiple sclerosis and was compared with the ADC of normal white matter in 16 age- and sex-matched control subjects. Seventy-five nonenhancing lesions (29 isointense, 46 hypointense) and 32 enhancing lesions (6 isointense, 26 hypointense) were categorized on the basis of unenhanced T1-weighted MR imaging. RESULTS: Hypointense and isointense nonenhancing lesions both showed significantly higher ADC than normal white matter (p < 0.0001). Hypointense nonenhancing lesions showed higher ADC values than isointense nonenhancing lesions (p < 0.0001). Diffusion in enhancing portions of enhancing lesions was decreased when compared with nonenhancing portions. CONCLUSION: Quantitative diffusion data from MR imaging differ among multiple sclerosis lesions that appear different from each other on T1-weighted images. These quantitative diffusion differences imply microstructural differences, which may prove useful in documenting irreversible disease.     

Evolution of multiple sclerosis lesions on serial contrast-enhanced T1-weighted and magnetization-transfer MR images

BACKGROUND AND PURPOSE: Magnetization-transfer imaging is a technique that could provide indirect evidence of the characteristics of multiple sclerosis (MS) lesions. The purpose of this work was to study the evolution of MS lesions on T1-weighted MR images over time and to investigate changes in magnetization-transfer ratio (MTR) values of MS lesions with different initial appearances on contrast-enhanced T1-weighted images. METHODS: Eleven patients with relapsing-remitting MS were studied with MR imaging. The MTRs were calculated for 47 lesions that had been classified according to their appearance on contrast-enhanced T1-weighted images. Each patient was examined at four time points over a 1-year period. The MTR changes observed in the selected lesions were compared with their initial T1-weighted appearance. RESULTS: The lowest MTR values were initially found in hypointense nonenhancing lesions and in ring-enhancing lesions, with both types showing a hypointense center. Changes in MTR values were more dynamic and reversible in ring-enhancing than in hypointense nonenhancing plaques. Nodular-enhancing lesions had slightly lower initial MTRs than did isointense non-enhancing lesions. CONCLUSION: The absence or presence of contrast uptake may indicate a different pathologic basis for hypointense MS lesions on T1-weighted MR images. These differences should be kept in mind when considering T1 lesion load as a surrogate marker of disability in MS.     

Improved detection of enhancing and nonenhancing lesions of multiple sclerosis with magnetization transfer.

PURPOSETo determine whether magnetization transfer imaging can improve visibility of contrast enhancement of multiple sclerosis plaques.METHODSFifty-nine enhancing and 63 nonenhancing lesions in 10 patients with multiple sclerosis were evaluated to calculate contrast-to-noise ratios on conventional T1-weighted and T1-weighted magnetization transfer images. The signal intensity of the lesion and the background (white matter) were measured on precontrast T1-weighted and T1-weighted magnetization transfer images (800/20/1 [repetition time/echo time/excitations]) and on postcontrast T1-weighted and T1-weighted magnetization transfer images. Mean contrast-to-noise ratios was calculated for all lesions.RESULTSThe contrast-to-noise ratio was significantly higher for enhancing and nonenhancing lesions on T1-weighted magnetization transfer images than on conventional T1-weighted images. For enhancing lesions, the contrast-to-noise ratio was significantly higher on postcontrast T1-weighted magnetization transfer images, 32 +/- 2 compared with 21 +/- 2 on conventional T1-weighted images. Fifty of the 59 enhancing lesions were seen on both the T1-weighted and the T1-weighted magnetization transfer images. Nine enhancing lesions were seen only on the postcontrast T1-weighted magnetization transfer images. In addition, of 63 nonenhancing lesions seen on proton-density, T2-weighted, and T1-weighted magnetization transfer images, 16 were not seen on the conventional T1-weighted images. Seven of the 63 nonenhancing lesions and 7 of the 59 enhancing lesions had high signal intensity on the precontrast T1-weighted magnetization transfer images suggestive of lipid signal, a finding not seen on the conventional precontrast T1-weighted images.CONCLUSIONMagnetization transfer improves the visibility of enhancing multiple sclerosis lesions, because they have a higher contrast-to-noise ratio than conventional postcontrast T1-weighted images. High signal intensity on both nonenhancing and enhancing lesions noted only on precontrast T1-weighted magnetization transfer suggests a lipid signal was unmasked. If magnetization transfer is used in multiple sclerosis patients, a precontrast magnetization transfer image is necessary.     

Single-dose gadolinium with magnetization transfer versus triple-dose gadolinium in the MR detection of multiple sclerosis lesions.

PURPOSETo compare the efficacy of single-dose gadolinium with magnetization transfer contrast (MTC) with that of triple-dose gadolinium in detecting enhancing multiple sclerosis lesions.METHODSTwenty-one patients with multiple sclerosis were examined with MR imaging first with 0.1 mmol/kg gadolinium (single dose) and then, after 24 to 72 hours, with 0.3 mmol/kg gadolinium (triple dose). T2-weighted fast spin-echo and T1-weighted spin-echo MR images with and without MTC were obtained before contrast administration followed by either T1-weighted spin-echo images with MTC (single dose) or conventional T1-weighted spin-echo images (triple dose), starting 5, 17, and 29 minutes after contrast administration. All images were evaluated in a blinded fashion and scored in random order by two readers. Outcome parameters included number of enhancing lesions, number of active MR examinations (those containing at least one enhancing lesion), contrast ratio (signal intensity of enhancing lesion divided by signal intensity of normal-appearing white matter), and size of enhancing lesions.RESULTSEighty-one percent more enhancing lesions and 49% more active MR examinations were detected when a triple dose of gadolinium was used as compared with a single dose. The level of agreement between readers as to the number of enhancing lesions was significantly higher for triple-dose than for single-dose gadolinium. With triple-dose gadolinium, contrast ratios and areas of enhancement increased by 10% and 33%, respectively. Delayed imaging increased the size of the lesion by 11% on single-dose MTC images and by 18% on triple-dose images.CONCLUSIONTriple-dose gadolinium is more effective (higher sensitivity and interobserver agreement) than single-dose gadolinium in combination with MTC in detecting enhancing multiple sclerosis lesions.     

Coefficient D(av) is more sensitive than fractional anisotropy in monitoring progression of irreversible tissue damage in focal nonactive multiple sclerosis lesions

BACKGROUND AND PURPOSE: Persistently hypointense lesions on T1-weighted MR images have been shown to correlate with the amount of axonal damage and clinical disability in multiple sclerosis (MS) patients. The purpose of this study was to investigate whether diffusion coefficient D(av) and fractional anisotropy (FA) are able to detect quantifiable differences among three groups of focal nonactive multiple sclerosis (MS) lesions that appear qualitatively different on T1-weighted images. METHODS: Conventional and diffusion tensor MR images of the brain were obtained in 18 patients with relapsing remitting (n = 10) or secondary progressive (n=8) MS and in 18 healthy volunteers. Focal nonactive MS lesions were classified as T1 isointense, T1 mildly hypointense, and T1 severely hypointense on unenhanced T1-weighted images. Differences among groups were assessed with one-way analysis of variance using the T1 lesion appearance as the grouping factor and either FA or coefficient D(av) as the dependent measure. RESULTS: FA was lowest and coefficient D(av) was highest in T1 severely hypointense lesions, and then, in ascending and descending order, respectively, T1 mildly hypointense lesions and T1 isointense lesions. A significant difference in the values of FA was detected only between T1 isointense lesions and T1 severely hypointense lesions (P <.01), whereas no difference was found between T1 mildly hypointense lesions and either one of these two groups. A significant difference was found in the values of coefficient D(av) among all investigated lesion groups. Coefficient D(av) was found to correlate inversely with the T1-weighted contrast ratio (r=-0.58, P <.0001), whereas FA and deltaFA (percentage of FA variation in the lesion, a relative FA measure that minimizes the effect of FA spatial dependence) were not. CONCLUSION: Coefficient D(av) is more sensitive than FA to variations in the degree of T1 hypointensity and, thus, in the amount of the permanent brain tissue damage in patients with MS.     

Proton MR spectroscopy and magnetization transfer ratio in multiple sclerosis: correlative findings of active versus irreversible plaque disease.

PURPOSETo characterize plaques of multiple sclerosis (MS) using both proton MR spectroscopy and magnetization transfer (MT) imaging.METHODSThe magnetization transfer ratio (MTR) was calculated from two series of three-dimensional gradient-recalled acquisition in the steady state (GRASS) images obtained with and without an MT saturation pulse. Proton spectra were acquired using the point-resolved spectroscopy (PRESS) sequence with a voxel size of 1.5 x 1.5 x 1.5 cm3. A total of 28 spectra were obtained in 13 patients who had clinically definitive MS. The spectra were analyzed together with the MTR.RESULTSA positive relationship was found between the N-acetylaspartate (NAA)/creatine (Cr) ratio and the MTR in MS plaques, whereas no significant correlation was found between the metabolite ratios and the signal intensity on fast spin-echo T2-weighted MR images.CONCLUSIONSmall changes in the MTR of MS plaques relative to the MTR of normal white matter may reflect inflammatory changes and edema, whereas larger changes in MTR correlate with decreased NAA/Cr ratio and therefore suggest demyelination and irreversible damage from chronic MS plaques.     

Quantification of magnetization transfer rate and native T1 relaxation time of the brain: correlation with magnetization transfer ratio measurements in patients with multiple sclerosis

The purpose of this paper is to perform quantitative measurements of the magnetization transfer rate (Kfor) and native T1 relaxation time (T1free) in the brain tissue of normal individuals and patients with multiple sclerosis (MS) by means of multiple gradient echo acquisitions, and to correlate these measurements with the magnetization transfer ratio (MTR). Quantitative magnetization transfer imaging was performed in five normal volunteers and 12 patients with relapsing–remitting MS on a 1.5 T magnetic resonance (MR) scanner. The T1 relaxation time under magnetization transfer irradiation (T1sat) was calculated by means of fitting the signal intensity over the flip angle in several 3D spoiled gradient echo acquisitions (3°, 15°, 30°, and 60°), while a single acquisition without MT irradiation (flip angle of 3°) was utilized to calculate the MTR. The Kfor and T1free constants were quantified on a pixel-by-pixel basis and parametric maps were reconstructed. We performed 226 measurements of Kfor, T1free, and the MTR on normal white matter (NWM) of healthy volunteers (n=50), and normal-appearing white matter (NAWM) and pathological brain areas of MS patients (n=120 and 56, respectively). Correlation coefficients between Kfor–MTR, T1free–MTR, and T1free–Kfor were calculated. Lesions were classified, according to their characteristics on T1-weighted images, into isointense (compared to white matter), mildly hypointense (showing signal intensity lower than white matter and higher than gray matter), and severely hypointense (revealing signal intensity lower than gray matter). Dirty white matter (DWM) corresponded to areas with diffused high signal, as identified on T2-weighted images. Strong correlation coefficients were obtained between MTR and Kfor for all lesions studied (r²=0.9, p<0.0001), for mildly hypointense plaques (r²=0.82, p<0.0001), and for DWM (r²=0.78, p=0.0007). In contrast, comparison between MTR and T1free values yielded rather low correlation coefficients for all groups assessed. In severely hypointense lesions, an excellent correlation was found between Kfor and T1free measurements (r²=0.98, p<0.0001). Strong correlations between Kfor and T1free were found for the rest of the subgroups, except for the NAWM, in which a moderate correlation was obtained (r²=0.5, p<0.0001). We conclude that Kfor and T1free measurements are feasible and may improve our understanding of the pathological brain changes that occur in MS patients.     

Is the magnetization transfer ratio a marker for myelin in multiple sclerosis?

Purpose

To investigate the correlation between water content (WC) and magnetization transfer ratio (MTR) in normal and multiple sclerosis (MS) brain. The MTR has been proposed as a marker for myelin in central nervous system tissue. However, changes in WC due to inflammation and edema may also affect the MTR.

Materials and Methods

Seven MS subjects with active disease and seven age‐ and gender‐matched controls were scanned using quantitative magnetic resonance techniques. WC, myelin water content, T₁ relaxation time, and MTR were calculated from areas of lesion (divided into new lesions less than 2 months old, isointense T₁ lesions, and hypointense T₁ lesions), contralateral normal‐appearing white matter (NAWM), and location‐matched normal white matter (NWM) in controls. Linear regression was used to determine the correlation between WC and MTR.

Results

A significant correlation was found between WC and MTR across all tissue (R = ?0.65, P < 0.0005).

Conclusion

MTR was correlated with WC in MS tissue, indicating that inflammation and edema influence MTR. Therefore, caution should be used when associating MTR exclusively with myelin content. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

The variable MR appearance of primary lymphoma of the central nervous system: comparison with histopathologic features.

PURPOSETo describe the MR features of primary central nervous system (CNS) lymphoma and to determine whether there is a correlation with histopathologic findings.METHODSThe MR images, pathologic specimens, and clinical records of 23 patients with primary CNS lymphoma were reviewed. The imaging and pathologic characteristics were tabulated and compared by using the standard tests for association in a two-dimensional contingency table.RESULTSA total of 61 lesions were present in 23 patients; 12 patients (52%) had multiple lesions. All lesions were isointense or hypointense on T1-weighted images, and 53% were isointense or hypointense on T2-weighted images. Twenty patients received intravenous contrast material, and 43 (91%) of 47 lesions enhanced. The three patients who had nonenhancing lesions received steroids before the initial MR studies. Enhancement patterns differed between the immunocompetent and the immunocompromised hosts, with the latter group harboring a higher percentage of rim-enhancing lesions. Twenty-seven (44%) of the lesions were centered in a cerebral hemisphere and 14 (23%) were centered in the central gray matter. There was a statistically significant correlation between a higher degree of necrosis histologically and hyperintensity on T2-weighted MR images. The degree of necrosis also showed a positive correlation with rim enhancement.CONCLUSIONSPrimary CNS lymphoma has a variable MR appearance that correlates with the severity of intratumoral necrosis. These imaging characteristics, as well as lesion location, mean lesion size, and proclivity to harbor necrosis, are altered in the immunocompromised host.     

Cortical/subcortical disease burden and cognitive impairment in patients with multiple sclerosis

BACKGROUND AND PURPOSE: We assessed whether the extent of macro- and microscopic disease in the cortical and subcortical brain tissue, as revealed by MR and magnetization transfer (MT) imaging, correlates with cognitive dysfunction in patients with multiple sclerosis (MS). METHODS: Dual-echo rapid acquisition with relaxation enhancement (RARE), fast fluid-attenuated inversion recovery (fast-FLAIR), T1-weighted, and MT MR images of the brain were obtained from 16 MS patients with cognitive impairment and from six without. Impaired and unimpaired patients were similar across demographic and other disease-related variables. Total and cortical/subcortical lesion loads were assessed using RARE, fast-FLAIR, and T1-weighted sequences. In each patient, cortical/subcortical disease was also assessed by means of MT ratio (MTR) histographic analysis. RESULTS: All the impaired patients had multiple hyperintense lesions in the cortical/subcortical regions on both RARE and fast-FLAIR images; two unimpaired patients had such lesions on the RARE images and four had them on the fast-FLAIR images. Total and cortical/subcortical RARE/fast-FLAIR hyperintense and T1 hypointense lesion loads were significantly greater in the group of cognitively impaired patients. Patients with cognitive deficits also had significantly lower MTR histographic values for all the variables. A multivariate regression model showed that average cortical/subcortical brain MTR was the only factor that was significantly associated with cognitive impairment. CONCLUSION: The extent and severity of MS disease in the cortical and subcortical regions significantly influence the cognitive functions of MS patients. MTR histographic findings suggest that subtle changes undetectable by conventional imaging are also important in determining MS cognitive decline.     

Magnetization transfer: a potential method to determine the age of multiple sclerosis lesions.

PURPOSETo determine whether magnetization transfer contrast can differentiate acute from chronic lesions in multiple sclerosis.METHODSThirteen patients with multiple sclerosis and eight healthy patients were studied with MR using a 0.1-T system. Relatively T2-weighted spin-echo images were obtained without and with magnetization transfer contrast. The magnetization transfer effect of multiple sclerosis lesions was calculated and compared with the ages of the lesions. The magnetization transfer effect of normal-appearing white matter in patients with multiple sclerosis was calculated and compared with the magnetization transfer effect of white matter in healthy volunteers. Statistical analysis was performed.RESULTSWhite matter in the healthy volunteers had values from 0.40 to 0.45. Normal-appearing white matter in the patients with multiple sclerosis had magnetization transfer effect values ranging from 0.41 to 0.45. Multiple sclerosis plaques of less than 1 year''s duration had magnetization transfer effect values ranging from 0.05 to 0.26; older plaques had values from 0.25 to 0.41. The difference in the distributions of these values for acute and chronic multiple sclerosis plaques is statistically significant.CONCLUSIONCurrent imaging modalities do not differentiate acute multiple sclerosis lesions from chronic ones. Our data on magnetization transfer show a statistically significant difference in magnetization transfer effect values between lesions of less than 1 year''s duration and older lesions. The different values may correspond to the histologic changes of multiple sclerosis plaques over time. Magnetization transfer may be a reliable method for determining the age of multiple sclerosis lesions.     

Abdominal tuberculous lymphadenopathy: MRI features

The aim of this study was to describe the MRI features of abdominal tuberculous lymphadenopathy. MRI studies of 13 patients with abdominal tuberculous lymphadenopathy were reviewed with regard to anatomic distribution and size. Signal intensities, in relation to abdominal wall muscle, on unenhanced T1- and T2-weighted images and patterns of contrast enhancement of lymphadenopathy were evaluated in each patient. In each patient, the largest lymph node with the same imaging characteristic was evaluated. The upper paraaortic region was the most common site of involvement (n=12 patients), followed by the lesser omentum (n=10 patients), the anterior pararenal space (n=9 patients), the lower paraaortic area (n=8 patients), the small bowel mesentery (n=6 patients), the greater omentum (n=2 patients) and the originating site of the inferior mesenteric artery (n=2 patients). The mean lymph node size was 1.8 cm (range 0.5–5 cm). The overall mean lymph node number per patient was 16 (range 2–50). A total of 41 lymph nodes were evaluated in 13 patients. On T2-weighted images, 40 lesions were hyperintense and one lesion was isointense. Nine hyperintense lesions showed a hypointense peripheral rim and seven internal heterogeneïty. Perinodal T2-hyperintensity was present in 23 lesions. The latter finding was valid for all patients. On T1-weighted images, 30 lesions were hypointense and 11 isointense. Nine hypointense lesions demonstrated a hyperintense peripheral rim, and six were heterogeneous. Contrast-enhanced fat-suppressed T1-weighted images demonstrated predominant peripheral enhancement in 28 lesions: (1) peripheral uniform, thin (n=19); (2) thick irregular, complete (n=3); and (3) conglomerate group of nodes showing peripheral and central areas of rim enhancement (n=6). Heterogeneous and homogeneous enhancement was present in ten and three lesions, respectively. Combinations of enhancing patterns in the same nodal group and different nodal groups were seen in eight and nine patients, respectively. Abdominal tuberculous lymphadenopathy may show a variety of signal intensities and patterns of contrast enhancement on MRI. Lymphadenopathy, hypointense on T1-weighted, hyperintense on T2-weighted images with perinodal hyperintensity, and predominant peripheral rimlike enhancement may suggest the diagnosis of tuberculosis.     

肝脏孤立性坏死结节的MRI表现

目的 总结肝脏孤立性坏死结节(SNN)平扫和动态增强MRI特征性表现.方法 回顾性分析经手术病理证实的15例SNN的MRI征象,对病灶数目、形状、大小、部位、边界、平扫和增强后信号及强化方式进行评价.结果 病灶单发14例,另1例有2个病灶.平扫T1WI及T2WI各发现15和14个病灶,增强扫描发现16个病灶.14个病灶最大径≤3 cm.平扫T1WI病灶呈低信号5个,略低信号9个,1个呈等信号伴有周边低信号包膜及内部点状低信号.在T2WI病灶呈高信号5个,略高信号4个,略低信号3个,明显低信号2个,其中2个病灶内见点状或细线样极高信号.16例在增强扫描后各期均呈低信号,尤其在门静脉期及延迟期呈明显低信号,边界及形态显示清楚.12个病灶形状不规则,4个病灶呈圆形或卵圆形.增强后病灶内部均未见强化,3个病灶在门静脉期及延迟期可见细环状轻度强化的包膜.结论 SNN特征性MRI表现有助于与肝脏其他肿瘤鉴别.     

Intradural schwannomas of the spine: MR findings with emphasis on contrast-enhancement characteristics.

Intradural extramedullary schwannomas are nerve sheath neoplasms that consist of focal proliferations of Schwann cells involving a spinal nerve. We reviewed the MR findings in seven patients with pathologically proved intradural schwannomas. The contrast-enhancement characteristics on MR images were determined and compared with the histologic features of the tumor. Six lesions were variably hyperintense on T2-weighted images and one was uniformly hypointense compared with the signal intensity of the spinal cord. Signal on T1-weighted images ranged from hypointense to isointense. All seven tumors showed heterogeneous enhancement; in five, the enhancement involved only the periphery of the lesion. The pattern of enhancement did not correlate with the signal characteristics noted on unenhanced T1- and T2-weighted images. Pathologically, hyaline thickening of vessel walls and cyst formation were prevalent in the peripherally enhancing lesions. However, enhancement did not correlate with the relative proportion of Antoni type A and type B tissue. Recognition of the MR characteristics of intradural extramedullary schwannomas may be helpful in the differential diagnosis of spinal tumors. In particular, peripheral contrast enhancement of an intradural extramedullary tumor on MR images should suggest the diagnosis of schwannoma.     

Correlation of spectroscopy and magnetization transfer imaging in the evaluation of demyelinating lesions and normal appearing white matter in multiple sclerosis

Magnetization transfer imaging (MT) and localized proton spectroscopy (¹H-MRS) were utilized in the evaluation of lesioins (high signal abnormalities on T₂-weighted images) and normal-appearing white matter (NAWM) in multiple sclerosis (MI). Eleven patients with a clinical diagnosis of MS were independently evaluated with both ¹H-MRS and MT. The magnetization transfer ratio (MTR) of lesions was compared with the relative concentration of Kacetyl-aspartate (NAA) and a composite peak at 2.1 to 2.6 ppm termed “marker peaks”. The MTR of white matter lesions in the MS patients was markedly decreased (6–34%; normal ≈?42%), and correlated well with increase in the marker peaks region (0.94–3.89). There was no correlation between the relative concentration of NAA and MTR. Increased resonance peaks in the 2.1 to 2.6 ppm range and marked decreases in MTR may be a relatively specific indicators of demyelination.     

T2 relaxation time analysis in patients with multiple sclerosis: correlation with magnetization transfer ratio

The aim of the current study was to perform T2 relaxation time measurements in multiple sclerosis (MS) patients and correlate them with magnetization transfer ratio (MTR) measurements, in order to investigate in more detail the various histopathological changes that occur in lesions and normal-appearing white matter (NAWM). A total number of 291 measurements of MTR and T2 relaxation times were performed in 13 MS patients and 10 age-matched healthy volunteers. Measurements concerned MS plaques (105), NAWM (80), and dirty white matter (DWM; 30), evenly divided between the MS patients, and normal white matter (NWM; 76) in the healthy volunteers. Biexponential T2 relaxation-time analysis was performed, and also possible linearity between MTR and mean T2 relaxation times was evaluated using linear regression analysis in all subgroups. Biexponential relaxation was more pronounced in black-hole lesions (16.6%) and homogeneous enhancing plaques (10%), whereas DWM, NAWM, and mildly hypointense lesions presented biexponential behavior with a lower frequency(6.6, 5, and 3.1%, respectively). Non-enhancing isointense lesions and normal white matter did not reveal any biexponentional behavior. Linear regression analysis between monoexponential T2 relaxation time and MTR measurements demonstrated excellent correlation for DWM(r=–0.78, p<0.0001), very good correlation for black-hole lesions(r=-0.71, p=0.002), good correlation for isointense lesions(r=–0.60, p=0.005), moderate correlation for mildly hypointense lesions(r=–0.34, p=0.007), and non-significant correlation for homogeneous enhancing plaques, NAWM, and NWM. Biexponential T2 relaxation-time behavior is seen in only very few lesions (mainly on plaques with high degree of demyelination and axonal loss). A strong correlation between MTR and monoexponential T2 values was found in regions where either inflammation or demyelination predominates; however, when both pathological conditions coexist, this linear relationship is lost.     

Focal nodular hyperplasia of the liver: assessment with contrast-enhanced TurboFLASH MR imaging

Twenty-two patients with 25 cases of focal nodular hyperplasia (FNH) proved with pathologic study were imaged with a TurboFLASH (fast low angle shot) sequence combined with bolus administration of gadolinium tetraazacyclododecanetetraacetic acid (DOTA), spin-echo (SE) T2-weighted sequences, and postcontrast T1-weighted sequences. FNH-liver signal-difference-to-noise ratios were quantified; the features of the central scar were qualitatively analyzed. On SE T2-weighted images, all FNHs were hyperintense; in two cases the central scar exhibited a high signal intensity associated with hypointense areas corresponding to fibrous tissue within the branches of the scar. Unenhanced TurboFLASH images always demonstrated the FNHs as hypointense and always depicted the central scar as a hypointense area within the lesion. After bolus injection, arterial enhancement of FNH was clearly seen, and in 10 of 25 lesions, enhancement within the scar was seen 40-80 seconds after injection. Both unenhanced and enhanced TurboFLASH sequences produced the best signal-difference-to-noise ratios in comparison with T2-weighted images.