Role of fluid-attenuated inversion recovery in the diagnosis of meningitis: comparison with contrast-enhanced magnetic resonance imaging

OBJECTIVE: Fluid-attenuated inversion recovery (FLAIR) has shown promise in the detection of subarachnoid space disease. The exact role of FLAIR in the diagnosis of meningitis has not been established. The purpose of this study was to evaluate FLAIR in the detection of meningitis in comparison with contrast-enhanced T1-weighted images (T1WI) in a blinded-reader study. We describe hyperintense sulci (HS) on FLAIR sequence in meningitis in relation to cerebrospinal fluid (CSF) protein and effective echo time (TE). METHODS: Two observers blinded to clinical information reviewed magnetic resonance (MR) images of patients with the diagnosis of meningitis and those of age-matched controls. The diagnosis was confirmed from chart review and CSF results. FLAIR images were obtained with 2 different TE values of 120 milliseconds and 150 milliseconds. FLAIR changes were correlated with CSF protein concentration and contrast-enhanced T1WI. RESULTS: Twenty-eight MR images of meningitis patients were reviewed. There were 23 abnormal MR images including 16 abnormal FLAIR scans with hyperintense sulci and 23 with leptomeningeal enhancement on contrast-enhanced T1WI. HS on FLAIR correlated with leptomeningeal enhancement on contrast-enhanced T1WI. Four viral and 1 bacterial meningitis had normal MR images (FLAIR and postcontrast TIWI). Two different TE values were used: 120 milliseconds (n = 15) and 150 milliseconds (n = 13). All patients with effective TE of 150 milliseconds. and CSF protein of more than 132 mg/dL had hyperintense sulci whereas patients with effective TE of 120 milliseconds and CSF protein of 257 mg/dL or more had HS. CONCLUSIONS: The sensitivity of contrast-enhanced T1WI was higher than FLAIR. HS on FLAIR correlated with contrast enhancement on T1WI. However, the sensitivity of FLAIR depends on CSF protein concentration threshold for (CSF hyperintensity) for a given effective TE. FLAIR cannot replace contrast-enhanced T1WI in diagnosing meningitis.     

Cortical lesions in multiple sclerosis: combined postmortem MR imaging and histopathology

BACKGROUND AND PURPOSE: Cortical lesions constitute a substantial part of the total lesion load in multiple sclerosis (MS) brain. They have been related to neuropsychological deficits, epilepsy, and depression. However, the proportion of purely cortical lesions visible on MR images is unknown. The aim of this study was to determine the proportion of intracortical and mixed gray matter (GM)-white matter (WM) lesions that can be visualized with postmortem MR imaging. METHODS: We studied 49 brain samples from nine cases of chronic MS. Tissue sections were matched to dual-echo T2-weighted spin-echo (T2SE) MR images. MS lesions were identified by means of myelin basic protein immunostaining, and lesions were classified as intracortical, mixed GM-WM, deep GM, or WM. Investigators blinded to the histopathologic results scored postmortem T2SE and 3D fluid-attenuated inversion recovery (FLAIR) images. RESULTS: Immunohistochemistry confirmed 70 WM, eight deep GM, 27 mixed GM-WM, and 63 purely cortical lesions. T2SE images depicted only 3% of the intracortical lesions, and 3D FLAIR imaging showed 5%. Mixed GM-WM lesions were most frequently detectable on T2SE and 3D FLAIR images (22% and 41%, respectively). T2SE imaging showed 13% of deep GM lesions versus 38% on 3D FLAIR. T2SE images depicted 63% of the WM lesions, whereas 3D FLAIR images depicted 71%. Even after side-by-side review of the MR imaging and histopathologic results, many of the intracortical lesions could not be identified retrospectively. CONCLUSION: In contrast to WM lesions and mixed GM-WM lesions, intracortical lesions remain largely undetected with current MR imaging resolution.     

Long component time constant of 23Na T*2 relaxation in healthy human brain.

Signal intensity in 23Na images is altered in pathologic conditions such as ischemia and may provide information regarding tissue viability complementary to MR diffusion and perfusion imaging. However, the multicomponent transverse relaxation of 23Na (spin 3/2) complicates the determination of tissue sodium concentration from 23Na images with nonzero echo-time. The purpose of this study was to measure the long component time constant of tissue sodium T*2 relaxation in the healthy human brain at 4 T. Multiecho gradient-echo 23Na images (10 echo-times ranging from 3.8-68.7 ms) were acquired in five healthy human volunteers. T*2 was quantified on a pixel-by-pixel basis using a nonnegative least squares fitting routine using 100 equally spaced bins between 0.5-99.5 ms and parametric maps were produced representing components between 0.5-3, 3.1-50, 50.1-98, and 98.1-99.5 ms. The long T*2 component of tissue sodium (average +/- standard deviation) varied between cortex (occipital = 22.0 +/- 2.4 ms), white matter (parietal = 18.2 +/- 1.9 ms), and subcortical gray matter (thalamus = 16.9 +/- 2.4 ms). These results demonstrate considerable regional variability and establish a foundation for future characterization of 23Na T*2 in conditions such as cerebral ischemia and cancer.     

Increased signal in the subarachnoid space on fluid-attenuated inversion recovery imaging associated with the clearance dynamics of gadolinium chelate: a potential diagnostic pitfall

BACKGROUND AND PURPOSE: Hyperintense CSF in the subarachnoid space (SAS) on fluid-attenuated inversion recovery (FLAIR) imaging has been reported in numerous pathologic conditions, including subarachnoid hemorrhage, meningitis, meningeal carcinomatosis, superior sagittal thrombosis, adjacent tumors, status epilepticus, and stroke. It has also been reported in otherwise healthy patients undergoing anesthesia with supplemental oxygen. We present a series of 11 patients with hyperintense CSF signal intensity in the SAS on FLAIR imaging after previous administration of gadolinium chelate. MATERIALS AND METHODS: Head MR images of patients who had a prior gadolinium-enhanced body, spine, or brain MR imaging and who had increased signal intensity in the SAS on FLAIR images were prospectively and retrospectively reviewed. Correlation was made with the clinical and laboratory findings. RESULTS: Eight of the 11 patients had negative findings on lumbar punctures. Seven patients had either chronic renal insufficiency or acute renal failure, but the remaining 4 had normal renal function. Nine patients had no other significant intracranial abnormalities, and 2 patients had acute infarcts remote from the CSF hyperintensity. One patient had follow-up studies at 24 and 48 hours, documenting resolution of the CSF hyperintensities. CONCLUSION: Given the sharp rise in volume of contrast-enhanced MR imaging studies, it is inevitable that some patients will have undergone a contrast-enhanced MR imaging 24-48 hours before an MR imaging of the brain. The neuroradiologist should be aware that previous administration of gadolinium chelate can cause increased signal intensity in the SAS on FLAIR imaging in patients with or without a history of renal insufficiency and without abnormalities known to disrupt the blood-brain barrier.     

Distribution of Brain Sodium Accumulation Correlates with Disability in Multiple Sclerosis: A Cross-sectional 23Na MR Imaging Study

Purpose: To quantify brain sodium accumulations and characterize for the first time the spatial location of sodium abnormalities at different stages of relapsing-remitting (RR) multiple sclerosis (MS) by using sodium 23 ((23)Na) magnetic resonance (MR) imaging. Materials and Methods: This study was approved by the local committee on ethics, and written informed consent was obtained from all participants. Three-dimensional (23)Na MR imaging data were obtained with a 3.0-T unit in two groups of patients with RR MS-14 with early RR MS (disease duration <5 years) and 12 with advanced RR MS (disease duration >5 years)-and 15 control subjects. Quantitative assessment of total sodium concentration (TSC) levels within compartments (MS lesions, white matter [WM], and gray matter [GM]) as well as statistical mapping analyses of TSC abnormalities were performed. Results: TSC was increased inside demyelinating lesions in both groups of patients, whereas increased TSC was observed in normal-appearing WM and GM only in those with advanced RR MS. In patients, increased TSC inside GM was correlated with disability (as determined with the Expanded Disability Status Scale [EDSS] score; P = .046, corrected) and lesion load at T2-weighted imaging (P = .003, corrected) but not with disease duration (P = .089, corrected). Statistical mapping analysis showed confined TSC increases inside the brainstem, cerebellum, and temporal poles in early RR MS and widespread TSC increases that affected the entire brain in advanced RR MS. EDSS score correlated with TSC increases inside motor networks. Conclusion: TSC accumulation dramatically increases in the advanced stage of RR MS, especially in the normal-appearing brain tissues, concomitant with disability. Brain sodium MR imaging may help monitor the occurrence of tissue injury and disability. ? RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112680/-/DC1.     

3D radial projection technique with ultrashort echo times for sodium MRI: clinical applications in human brain and skeletal muscle.

(23)Na MRI has the potential to noninvasively detect sodium (Na) content changes in vivo. The goal of this study was to implement (23)Na MRI in a clinical setting for neurooncological and muscular imaging. Due to the biexponential T(2) decay of the tissue Na signal with a short component, which ranges between 0.5-8 ms, the measurement of total Na content requires imaging techniques with echo times (TEs) below 0.5 ms. A 3D radial pulse sequence with a TE of 0.2 ms at a spatial resolution of 4 x 4 x 4 mm(3) was developed that allows the acquisition and presentation of Na images on the scanner. This sequence was evaluated in patients with low- and high-grade gliomas, and higher (23)Na MR signals corresponding to an increased Na content were found in the tumor regions. The contrast-to-noise ratio (CNR) between tumor and white matter increased from 0.8 +/- 0.2 to 1.3 +/- 0.3 with tumor grade. In patients with an identified muscular (23)Na channelopathy (Paramyotonia congenita (PC)), induced muscle weakness led to a signal increase of approximately 18% in the (23)Na MR images, which was attributed to intracellular Na(+) accumulation in this region.     

MRI of arachnoid granulations within the dural sinuses using a FLAIR pulse sequence

The purpose of the study was to assess the signal intensities of arachnoid granulations within the dural sinuses using the FLAIR sequence for differentiation of space-occupying lesions in and adjacent to the dural sinuses. We retrospectively reviewed MR images of the brain of 1118 consecutive subjects, ranging in age from 0 to 93 years (mean 57.2 years). Nodules within the dural sinuses with signal intensities similar to that of cerebrospinal fluid (CSF) on both T1 and T2 weighted images were defined as arachnoid granulations. The location, signal intensity on T1 weighted spin echo (SE), T2 weighted fast SE and FLAIR images, the impression on the inner table of the skull, and the size of the lesion were assessed. 112 subjects (10.0%), age range 4-89 years old (mean 58.9 years), were found to have 134 arachnoid granulations. The commonest location was the transverse sinus, with 115 granulations (85.8%). The prevalence of the granulations showed a peak in the sixth decade of age. All granulations were isointense relative to CSF on T2 weighted images and almost all lesions were isointense relative to CSF on T1 weighted images. On FLAIR images, 90.3% of the granulations were isointense relative to CSF and the other 9.7% granulations were slightly hyperintense compared with the CSF. 21 (15.7%) subjects showed impressions on the inner table; one case involved the outer table. In conclusion, arachnoid granulations were isointense or slightly hyperintense relative to CSF on FLAIR. FLAIR images are helpful in differentiating arachnoid granulations from other dural sinus lesions or skull lesions which have an intensity similar to that of CSF on T1 weighted and T2 weighted images.     

Supplemental oxygen causes increased signal intensity in subarachnoid cerebrospinal fluid on brain FLAIR MR images obtained in children during general anesthesia

PURPOSE: To prospectively test the hypothesis that high levels of the fraction of inspired oxygen (Fio(2)) during general anesthesia cause subarachnoid cerebrospinal fluid (CSF) hyperintensity during fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging. MATERIALS AND METHODS: At brain MR imaging during general anesthesia with propofol, two FLAIR sequences were performed in 20 children with American Society of Anesthesiologists physical status classification system grades of 3 or lower. The first FLAIR sequence was performed with the child breathing 100% oxygen; the second was performed with the child breathing 30% oxygen. CSF signal intensity was quantified on a three-point ordinal scale (0 = hypointense to brain parenchyma, 1 = isointense to brain parenchyma, 2 = hyperintense to brain parenchyma) by a pediatric neuroradiologist who was blinded to the Fio(2) level. The Wilcoxon signed rank test was used to determine if CSF hyperintensity was correlated with Fio(2). RESULTS: CSF hyperintensity was present in all 20 children (age range, 1.9-16.7 years; 12 children were boys) when the Fio(2) was 100%. The hyperintensity partially or completely disappeared in the basilar cisterns (P <.001) and cerebral sulcal subarachnoid space (P <.001) after Fio(2) was reduced from 100% to 30%. CONCLUSION: These findings are consistent with the hypothesis that increased arterial oxygen tension and consequently increased CSF Po(2) resulting from administration of high Fio(2) during general anesthesia are responsible for the increased CSF signal intensity noted on brain FLAIR MR images.     

Noninvasive quantification of total sodium concentrations in acute reperfused myocardial infarction using 23Na MRI.

The transport of sodium and potassium between the intra- and extracellular pools and the maintenance of the transmembrane concentration gradients are important to cell function and integrity. The early disruption of the sodium pump in myocardial infarction in response to the exhaustion of energy reserves following ischemia and reperfusion results in increased intracellular (and thus total) sodium levels. In this study a method for noninvasively quantifying myocardial sodium levels directly from sodium (23Na) MRI is presented. It was used to measure total myocardial sodium on a clinical 1.5T system in six normal dogs and five dogs with experimentally-induced myocardial infarction (MI). The technique was validated by comparing total sodium content measured by 23Na MRI with that measured by atomic absorption spectrophotometry (AAS) in biopsied tissue. Total sodium measured by 23Na MRI was significantly elevated in regions of infarction (81.3 +/- 14.3 mmol/kg wet wt, mean +/- SD) compared to noninfarcted myocardial tissue from both infarcted dogs (36.2 +/- 1.1, P < 0.001) and from normal controls (34.4 +/- 2.8, P < 0.0001). Myocardial tissue sodium content as measured by 23Na MRI did not vary regionally in the lateral, anterior, or inferior regions in normal hearts (ANOVA, P = NS). Sodium content measured by 23Na MRI agreed with the mean AAS estimates of 31.3 +/- 5.6 mmol/kg wet wt (P = NS) in normal hearts, and did not differ significantly from AAS measurements in MI (P = NS). Thus, local tissue sodium levels can be accurately quantified noninvasively using 23Na MRI in normal and acutely reperfused MI. The detection of regional myocardial sodium elevations may help differentiate viable from nonviable, infarcted tissue.     

Database of normal human cerebral blood flow measured by SPECT: II. Quantification of I-123-IMP studies with ARG method and effects of partial volume correction

The limited spatial resolution of SPECT causes a partial volume effect (PVE) and can lead to the significant underestimation of regional tracer concentration in the small structures surrounded by a low tracer concentration, such as the cortical gray matter of an atrophied brain. The aim of the present study was to determine, using 123I-IMP and SPECT, normal CBF of elderly subjects with and without PVE correction (PVC), and to determine regional differences in the effect of PVC and their association with the regional tissue fraction of the brain. METHODS: Quantitative CBF SPECT using 123I-IMP was performed in 33 healthy elderly subjects (18 males, 15 females, 54-74 years old) using the autoradiographic method. We corrected CBF for PVE using segmented MR images, and analyzed quantitative CBF and regional differences in the effect of PVC using tissue fractions of gray matter (GM) and white matter (WM) in regions of interest (ROIs) placed on the cortical and subcortical GM regions and deep WM regions. RESULTS: The mean CBF in GM-ROIs were 31.7 +/- 6.6 and 41.0 +/- 8.1 ml/100 g/min for males and females, and in WM-ROIs, 18.2 +/- 0.7 and 22.9 +/- 0.8 ml/100 g/min for males and females, respectively. The mean CBF in GM-ROIs after PVC were 50.9 +/- 12.8 and 65.8 +/- 16.1 ml/100 g/min for males and females, respectively. There were statistically significant differences in the effect of PVC among ROIs, but not between genders. The effect of PVC was small in the cerebellum and parahippocampal gyrus, and it was large in the superior frontal gyrus, superior parietal lobule and precentral gyrus. CONCLUSION: Quantitative CBF in GM recovered significantly, but did not reach values as high as those obtained by invasive methods or in the H2(15)O PET study that used PVC. There were significant regional differences in the effect of PVC, which were considered to result from regional differences in GM tissue fraction, which is more reduced in the frontoparietal regions in the atrophied brain of the elderly.     

Measurement of T1 and T2 in the cervical spinal cord at 3 tesla

T(1) and T(2) were measured for white matter (WM) and gray matter (GM) in the human cervical spinal cord at 3T. T(1) values were calculated using an inversion-recovery (IR) and B(1)-corrected double flip angle gradient echo (GRE) and show significant differences (p = 0.002) between WM (IR = 876 +/- 27 ms, GRE = 838 +/- 54 ms) and GM (IR = 973 +/- 33 ms, GRE = 994 +/- 54 ms). IR showed significant difference between lateral and dorsal column WM (863 +/- 23 ms and 899 +/- 18 ms, respectively, p = 0.01) but GRE did not (p = 0.40). There was no significant difference (p = 0.31) in T(2) between WM (73 +/- 6 ms) and GM (76 +/- 3 ms) or between lateral and dorsal columns (lateral: 73 +/- 6 ms, dorsal: 72 +/- 7 ms, p = 0.59). WM relaxation times were similar to brain structures with very dense fiber packing (e.g., corpus callosum), while GM values resembled deep GM in brain. Optimized sequence parameters for maximal contrast between WM and GM, and between WM and cerebrospinal fluid (CSF) were derived. Since the spinal cord has rostral-caudal symmetry, we expect these findings to be applicable to the whole cord.     

Peritumoral brain regions in gliomas and meningiomas: investigation with isotropic diffusion-weighted MR imaging and diffusion-tensor MR imaging

PURPOSE: To retrospectively measure the diffusion-weighted (DW) imaging characteristics of peritumoral hyperintense white matter (WM) and peritumoral normal-appearing WM, as seen on T2-weighted magnetic resonance (MR) images of infiltrative high-grade gliomas and meningiomas. MATERIALS AND METHODS: Seventeen patients with biopsy-proved glioma and nine patients with imaging findings consistent with meningioma and an adjacent hyperintense region on T2-weighted MR images were examined with DW and diffusion-tensor MR imaging. Apparent diffusion coefficients (ADCs) were measured on maps generated from isotropic DW images of enhancing tumor, hyperintense regions adjacent to enhancing tumor, normal-appearing WM adjacent to hyperintense regions, and analogous locations in the contralateral WM corresponding to these areas. Fractional anisotropy (FA) was measured in similar locations on maps generated from diffusion-tensor imaging data. Changes in ADC and FA in each type of tissue were compared across tumor types by using a two-sample t test. P <.05 indicated statistical significance. RESULTS: Mean ADCs in peritumoral hyperintense regions were 1.309 x 10(-3) mm2/sec (mean percentage of 181% of normal WM) for gliomas and 1.427 x 10(-3) mm2/sec (192% of normal value) for meningiomas (no significant difference). Mean ADCs in peritumoral normal-appearing WM were 0.723 x 10(-3) mm2/sec (106% of normal value) for gliomas and 0.743 x 10(-3) mm2/sec (102% of normal value) for meningiomas (no significant difference). Mean FA values in peritumoral hyperintense regions were 0.178 (43% of normal WM value) for gliomas and 0.224 (65% of normal value) for meningiomas (P =.05). Mean FA values for peritumoral normal-appearing WM were 0.375 (83% of normal value) for gliomas and 0.404 (100% of normal value) for meningiomas (P =.01). CONCLUSION: The difference in FA decreases in peritumoral normal-appearing WM between gliomas and meningiomas was significant, and the difference in FA decreases in peritumoral hyperintense regions between these tumors approached but did not reach significance. These findings may indicate a role for diffusion MR imaging in the detection of tumoral infiltration that is not visible on conventional MR images.     

Measurement of global brain atrophy in Alzheimer's disease with unsupervised segmentation of spin-echo MRI studies

In 16 patients with probable Alzheimer's disease (AD; NINDS criteria, age range 56-78 years), gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) absolute and fractional volumes were measured with an unsupervised multiparametric post-processing segmentation method based on estimates of relaxation rates R1, R2 (R1 = 1/T1; R2 = 1/T2) and proton density [N(H)] from conventional spin-echo studies (Alfano et al. Magn. Reson. Med. 1997;37:84-93). Global brain atrophy, and GM and WM fractions significantly correlated with Mini-Mental Status Examination and Blessed Dementia Scale scores. Compared with normals, brain compartments in AD patients showed decreased GM (-6.84 +/- 1.58%) and WM fractions (-9.79 +/- 2.47%) and increased CSF fractions (+58.80 +/- 10.37%). Changes were more evident in early-onset AD patients. In AD, measurement of global brain atrophy obtained by a computerized procedure based on routine magnetic resonance studies could complement the information provided by neuropsychological tests for the assessment of disease severity.     

Automated classification of multi-spectral MR images using Linear Discriminant Analysis

Magnetic resonance imaging (MRI) is a valuable instrument in medical science owing to its capabilities in soft tissue characterization and 3D visualization. A potential application of MRI in clinical practice is brain parenchyma classification. This work proposes a novel approach called “Unsupervised Linear Discriminant Analysis (ULDA)” to classify and segment the three major tissues, i.e. gray matter (GM), white matter (WM) and cerebral spinal fluid (CSF), from a multi-spectral MR image of the human brain. The ULDA comprises two processes, namely Target Generation Process (TGP) and Linear Discriminant Analysis (LDA) classification. TGP is a fuzzy-set process that generates a set of potential targets from unknown information, and applies these targets to train the optimal division boundary by LDA, such that three tissues GM, WM and CSF are separated. Finally, two sets of images, namely computer-generated phantom images and real MR images are used in the experiments to evaluate the effectiveness of ULDA. Experiment results reveal that UDLA segments a multi-spectral MR image much more effectively than either FMRIB's Automated Segmentation Tool (FAST) or Fuzzy C-means (FC).     

Unsupervised,automated segmentation of the normal brain using a multispectral relaxometric magnetic resonance approach

The purpose of this study was the development and testing of a method for unsupervised, automated brain segmentation. Two spin-echo sequences were used to obtain relaxation rates and proton-density maps from 1.5 T MR studies, with two axial data sets including the entire brain. Fifty normal subjects (age range, 16 to 76 years) were studied. A Three-dimensional (3D) spectrum of the tissue voxels was used for automatic segmentation of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) and for calculation of their volumes. Accuracy and reproducibility were tested with a three-compartment phantom simulating GM, WM, and CSF. In the normal subjects, a significant decrease of GM fractional volume and increased CSF volume with age were observed (P < 0.0001), with no significant changes in WM. This multi-spectral segmentation method permits reproducible, operator-independent volumetric measurements.     

Normal brain development and aging: quantitative analysis at in vivo MR imaging in healthy volunteers

PURPOSE: To quantitate neuroanatomic parameters in healthy volunteers and to compare the values with normative values from postmortem studies. MATERIALS AND METHODS: Magnetic resonance (MR) images of 116 volunteers aged 19 months to 80 years were analyzed with semiautomated procedures validated by means of comparison with manual tracings. Volumes measured included intracranial space, whole brain, gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF). Results were compared with values from previous postmortem studies. RESULTS: Whole brain and intracranial space grew by 25%-27% between early childhood (mean age, 26 months; age range, 19-33 months) and adolescence (mean age, 14 years; age range, 12-15 years); thereafter, whole-brain volume decreased such that volunteers (age range, 71-80 years) had volumes similar to those of young children. GM increased 13% from early to later (6-9 years) childhood. Thereafter, GM increased more slowly and reached a plateau in the 4th decade; it decreased by 13% in the oldest volunteers. The GM-WM ratio decreased exponentially from early childhood through the 4th decade; thereafter, it gradually declined. In vivo patterns of change in the intracranial space, whole brain, and GM-WM ratio agreed with published postmortem data. CONCLUSION: MR images accurately depict normal patterns of age-related change in intracranial space, whole brain, GM, WM, and CSF. These quantitative MR imaging data can be used in research studies and clinical settings for the detection of abnormalities in fundamental neuroanatomic parameters.     

Quantitative follow-up of patients with multiple sclerosis using MRI: technical aspects

A highly reproducible automated procedure for quantitative analysis of serial brain magnetic resonance (MR) images was developed for use in patients with multiple sclerosis (MS). The intracranial cavity (ICC) was identified on standard dual-echo spin-echo brain MR images using a supervised automated procedure. MR images obtained from one MS patient at 24 time points in the course of a 1-year follow-up were aligned with the images of one of the time points. Next, the contents of the ICC in each MR exam were segmented into four tissues, using a self-adaptive statistical algorithm. Misclassifications due to partial voluming were corrected using a combination of morphologic operators and connectivity criteria. Finally, a connectivity detection algorithm was used to separate the tissue classified as lesions into individual entities. Registration, classification of the contents of the ICC, and identification of individual lesions are fully automatic. Only identification of the ICC requires operator interaction. In each MR exam, the program estimated volumes for the ICC, gray matter (GM), white matter (WM), white matter lesions (WML), and cerebrospinal fluid (CSF). The reproducibility of the system was superior to that of supervised segmentation, as evidenced by the coefficient of variation: CSF supervised 45.9% vs. automated 7.7%, GM 16.0% vs. 1.4%, WM 15.7% vs. 1.3%, and WML 39.5% vs 52.0%. Our results demonstrate that this computerized procedure allows routine reproducible quantitative analysis of large serial MRI data sets.     

Fast method for brain image segmentation: application to proton magnetic resonance spectroscopic imaging.

The interpretation of brain metabolite concentrations measured by quantitative proton magnetic resonance spectroscopic imaging (MRSI) is assisted by knowledge of the percentage of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) within each MRSI voxel. Usually, this information is determined from T(1)-weighted magnetic resonance images (MRI) that have a much higher spatial resolution than the MRSI data. While this approach works well, it is time-consuming. In this article, a rapid data acquisition and analysis procedure for image segmentation is described, which is based on collection of several, thick slice, fast spin echo images (FSE) of different contrast. Tissue segmentation is performed with linear "Eigenimage" filtering and normalization. The method was compared to standard segmentation techniques using high-resolution 3D T(1)-weighted MRI in five subjects. Excellent correlation between the two techniques was obtained, with voxel-wise regression analysis giving GM: R2 = 0.893 +/- 0.098, WM: R2 = 0.892 +/- 0.089, ln(CSF): R2 = 0.831 +/- 0.082). Test-retest analysis in one individual yielded an excellent agreement of measurements with R2 higher than 0.926 in all three tissue classes. Application of FSE/EI segmentation to a sample proton MRSI dataset yielded results similar to prior publications. It is concluded that FSE imaging in conjunction with Eigenimage analysis is a rapid and reliable way of segmenting brain tissue for application to proton MRSI.     

Human skeletal muscle: sodium MR imaging and quantification-potential applications in exercise and disease

PURPOSE: To use sodium 23 magnetic resonance (MR) imaging to quantify noninvasively total sodium in human muscle and to apply the technique in exercise and musculoskeletal disease. MATERIALS AND METHODS: Total [Na] sodium was determined from the ratio of the relaxation-corrected (23)Na signal intensities measured from short echo-time (0.4 msec) (23)Na images to those from an external saline solution reference. The method was validated with the blinded use of saline solutions of varying sodium concentrations. [Na] was measured in the calf muscles in 10 healthy volunteers. (23)Na MR imaging also was performed in two healthy subjects after exercise, two patients with myotonic dystrophy, and two patients with osteoarthritis. RESULTS: (23)Na MR imaging yielded a total [Na] value of 28.4 mmol/kg of wet weight +/- 3.6 (SD) in normal muscle, consistent with prior biopsy data. Spatial resolution was 0.22 mL, with signal-to-noise ratio of 10-15. Mean signal intensity elevations were 16% and 22% after exercise and 47% and 70% in dystrophic muscles compared with those at normal resting levels. In osteoarthritis, mean signal intensity reductions were 36% and 15% compared with those in unaffected knee joints. CONCLUSION: (23)Na MR imaging can be used to quantify total [Na] in human muscle. The technique may facilitate understanding of the role of the sodium-potassium pump and perfusion in normal and diseased muscle.     

Diffusion-weighted echo-planar MR imaging in differential diagnosis of brain tumors and tumor-like conditions

We assess diffusion-weighted MR images in the differential diagnosis of intracranial brain tumors and tumor-like conditions. Heavily diffusion-weighted (b = 1100 or 1200 s/mm²) axial images were obtained with single-shot echo-planar technique in 93 patients with pathologically confirmed various intracranial tumors and tumor-like conditions with diffusion gradient perpendicular to the images. We compared signal intensity of the lesions with those of gray and white matter, and cerebrospinal fluid (CSF). In 29 cases (31.1 %) the lesions were isointense to gray and/or white matter. However, 5 cases (5.4 %) showed extremely increased signal intensity: two epidermoid cysts; two chordomas; and one brain abscess. The entire portion of a tumor was markedly hyperintense in 10 cases (10.8 %): four malignant lymphomas; four medulloblastomas; one germinoma; and one pineoblastoma. A CSF-like hypointense signal was seen in many cystic tumors, and cystic or necrotic portions of tumors. A neurosarcoid granulation was the only solid lesion showing characteristically a hypointense signal like CSF. The combination of markedly hyperintense and hypointense signals was seen generally in hemorrhagic tumors. Diffusion-weighted echo-planar MR imaging is useful in the differential diagnosis of brain tumors and tumor-like conditions, and suggests specific histological diagnosis in some cases. Received: 30 July 1999; Revised: 2 November 1999; Accepted: 9 December 1999