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PubMed2005

Isotropic diffusion weighting in radial fast spin-echo magnetic resonance imaging.

Radial fast spin-echo (radial-FSE) methods enable multishot diffusion-weighted MRI (DWMRI) to be carried out without significant artifacts due to motion and/or susceptibility and can be used to generate DWMRI images with high spatial resolution. In this work, a novel method that allows isotropic diffusion weighting to be obtained in a single radial k-space data set is presented. This is accomplished by altering the direction of diffusion weighting gradients between groups of TR periods, which yield sets of radial lines that possess diffusion weighting sensitive to motion in different directions. By altering the diffusion weighting directions and controlling the view ordering appropriately within the sequence, an effectively isotropic diffusion-weighted image can be obtained within one radial-FSE scan. The order in which radial lines are acquired can also be controlled to yield data sets without significant artifacts due to motion, T(2) decay, and/or diffusion anisotropy.

Anisotropy↗
PubMed2002

Acute transverse myelitis after Japanese B encephalitis vaccination in a 4-year-old girl.

Fourteen days after Japanese B encephalitis (JBE) vaccination, a 4-year-old girl developed the full clinical manifestation of ATM within 24h. She showed acute ascending flaccid paraplegia with sensory disturbance, bladder dysfunction and meningeal sign. Cerebrospinal fluid examination revealed neutrophil pleocytosis and elevated protein level. Magnetic resonance imaging (MRI) showed diffuse swelling of the cervical and lumbar cord with low signal intensity on T1 and high signal intensity on T2-weighted imaging. These findings suggested that she had developed meningo-radiculomyelopathy. Since sequential MRI studies showed prompt reduction of the cord swelling, the high-dose methylprednisolone therapy employed seemed to have been effective for improvement of inflammation. Even with such potent drug treatment, she still has substantial flaccid diplegia and sphincter disorder 1 year later, and so we are convinced that the pathological change of the cord was as severe as in necrotizing myelopathy. Although the pathological process remains unknown, cellular autoimmune mechanism against the JBE vaccination is suspected.

Acute Disease↗
PubMed2005

[Neurologic complications in the immediate postoperative period after cardiac surgery. Role of brain magnetic resonance imaging].

INTRODUCTION AND OBJECTIVES: Neurologic complications still cause significant morbidity and mortality in the immediate postoperative period following cardiac surgery. Our understanding of the pathogenesis, prevention, and management of these lesions is constantly developing. MATERIAL AND METHOD: We describe neurologic complications and their course in a cardiac surgery cohort and analyze the value of brain magnetic resonance imaging (MRI), using T1-weighted, T2-weighted, and FLAIR sequences, in patients with postoperative stroke or encephalopathy in whom CT scanning revealed no abnormalities explaining their clinical condition. RESULTS: In 688 patients studied postoperatively, we observed 57 neurologic complications (8.3%): 25 strokes, 24 encephalopathies, 5 seizure disorders, 2 brain deaths, and 1 intracranial hemorrhage. Initial CT scanning failed to show significant findings in 70%. 18 patients underwent brain MRI. In all but 1 of the 11 with stroke, MRI showed areas of acute or subacute infarction (i.e., hyperintensity in FLAIR or T2-weighted sequences) in different locations, mainly in a watershed distribution. In 3 of the 4 patients with mild-to-moderate encephalopathy, MRI showed lesions similar to those previously described for stroke. In the remaining 3 patients, who had severe encephalopathy, MRI showed diffuse cortical necrosis. CONCLUSIONS: The incidence of neurologic complications in the postoperative period following cardiac surgery is significant. In a high percentage of patients, brain CT scanning may not show pathologic findings. In selected patients, MRI could help identify areas of infarction not detected by CT. These images could improve clinicians' understanding of the pathogenic, pathophysiologic, clinical, and prognostic characteristics of such neurologic complications.

Adult↗
PubMed2006

Physiologic characterisation of glioblastoma multiforme using MRI-based hypoxia mapping, chemical shift imaging, perfusion and diffusion maps.

PURPOSE: A multiparametric, physiologic MRI approach was considered to more completely characterise biopsy-confirmed glioblastoma multiforme (GBM). Chemical shift imaging (CSI) supplied biochemical information in metabolite ratios, while perfusion images provided data on presumed vascularity from regional cerebral blood volume (rCBV) and permeability maps. Diffusion-weighted images were reduced to apparent diffusion coefficient (ADC) maps to evaluate cellularity, and blood oxygen level-dependent imaging was used to create maps of putative hypoxic regions. METHODS: Six post-treatment GBM patients were scanned at 3-month intervals until recurrence was suggested by conventional MRI parameters, yielding 20 scans for consideration. The percentage of extreme values in each technique that overlapped with other parameters was measured and compared across hemispheres to assess utility. RESULTS: We found significantly better performance in selecting the diseased hemisphere for overall percent overlap when compared to voxel counts from individual thresholded parameter maps. Parameters were selected on the basis of highest overlap, and corresponding composite overlap maps show increased specificity to likely recurrent regions by reducing the number of falsely positive voxels, and offer insight into relationships between various parameters. CONCLUSION: In a pilot group of patients, percent overlap appears to be sensitive to recurrent disease. When used to combine multiple parameters, voxels containing overlap can specifically target probable recurrent areas.

Brain Mapping↗
PubMed1999

Silent embolism in diagnostic cerebral angiography and neurointerventional procedures: a prospective study.

BACKGROUND: Cerebral angiography is associated with a small but definite risk of neurological complications with an unknown incidence of clinically silent embolism. We assessed the neurological complication rate compared with the frequency of silent embolism after angiography METHODS: We used diffusion-weighted magnetic resonance imaging (MRI) before and after angiography to assess embolic events. 100 consecutive angiographies (66 diagnostic and 34 interventional procedures) were done on 91 patients. Patients underwent neurological assessment before, immediately after, and 1 day after angiography. FINDINGS: Before angiography, no abnormalities were seen on diffusion-weighted MRI. Diffusion-weighted MRI showed 42 bright lesions in 23 patients after 23 procedures (17 diagnostic, six interventional) in a pattern consistent with embolic events. There was no new neurological deficit after any angiographic procedure. After diagnostic angiography in patients with a history of vasculopathy, the frequency of lesions was significantly higher than in patients without vascular risk factors (12 [44%] of 27 vs five [13%] of 39 patients, p=0.03). In diagnostic angiography, the appearance of lesions was significantly correlated with whether vessels were difficult to probe (p=0.01), amount of contrast medium needed (p<0.01), fluoroscopy time (p<0.01), and use of additional catheters (p=0.02). INTERPRETATION: After diagnostic and interventional cerebral angiography, embolic events are more frequent than the apparent neurological complication rate. In diagnostic procedures, the incidence of embolism is closely related to a vascular risk profile.

Adolescent↗
PubMed2006

[A case of hypoxic encephalopathy with unilateral laminar necrosis].

We reported a 67-year-old woman with unilateral laminar necrosis caused by hypoxic encephalopathy. She presented with sudden onset of dyspnea, unconsciousness and left hemiplegia. Although diffusion-weighted MRI image of the brain 14 hours after onset was indistinct, MRI on the 4th day showed right laminar necrosis. Cerebral angiography demonstrated complete obstruction of the right proximal common carotid artery and severe stenosis of the left internal carotid artery. We speculate that chronic ipsilateral obstruction of the internal carotid artery may modify the unique distribution of laminar necrosis. As shown in this case, laminar necrosis can be demonstrated only on subsequent MRI. If clinical suspicion of hypoxic encephalopathy is high, repeated MRI may be appropriate.

Aged↗
PubMed2006

Diffusion tensor imaging findings and their correlation with neuropsychological deficits in patients with temporal lobe epilepsy and interictal psychosis.

PURPOSE: To examine frontotemporal white-matter integrity in patients with temporal lobe epilepsy (TLE) and interictal psychosis. METHOD: Patients with TLE and interictal psychosis (IP; n = 20) were compared with age-matched TLE patients without psychosis (NIP; n = 20). Patients had either no focal lesions or hippocampal sclerosis on conventional MRI. Complete diffusion tensor imaging (DTI) data were available in 18 IP and 20 NIP patients. A region-of-interest (ROI) approach was used to determine the DTI measures, fractional anisotropy (FA) and mean diffusivity (MD), in the middle frontal and middle temporal gyri. The relation between the DTI measures and neuropsychological tests previously identified as impaired in the IP group was examined. RESULTS: The IP group had significantly lower FA values in both frontal and temporal regions and significantly higher MD in bilateral frontal regions. We found that performance on some neuropsychological tests was significantly related to frontotemporal FA reductions. CONCLUSIONS: Our findings suggest that subtle abnormalities in the frontotemporal white matter of patients with interictal psychosis may be undetectable on conventional MRI. These abnormalities may contribute to the cognitive deficits detected in these patients.

Adult↗
PubMed1996

Listeria spinal cord abscess--clinical and MRI findings.

BACKGROUND: Intramedullary spinal cord abscess due to Listeria Monocytogenes is an uncommon condition usually affecting immunocompromised patients. METHOD: Case study. RESULTS: A 69-year-old man presented with 3 weeks history of subacute paralysis of both lower limbs and the left upper limb. Myelogram and CT scan showed a widened upper cervical cord. CSF revealed lymphocytosis, moderately elevated protein and depressed glucose. A gadolinium-enhanced MRI showed diffuse cervical cord edema with two ring-enhancing lesions at C2-C3. Blood and CSF cultures grew Listeria Monocytogenes. He received IV ampicillin and gentamycin; the latter was discontinued after 1 month due to nephrotoxicity. Serial MRI over the next 3 months showed significant reduction in the size of these abscesses. The patient made a modest improvement in the power of his lower limbs, however he remained bed-ridden. Aside from being a mild, diet-controlled diabetic, there was no evidence of immunosuppression. CONCLUSION: Listeria spinal cord abscess is a treatable disorder and should be considered in the differential diagnosis in patients with a subacute onset of spinal cord dysfunction.

Abscess↗
PubMed2006

The role of MRS and fMRI in multiple sclerosis.

Multiple sclerosis is now recognized as more than simply a disease of inflammation and demyelination in the brain and spinal cord. Conventional MRI has been established as the most important paraclinical tool in the diagnostic assessment of patients with suspected MS, and in the monitoring of treatment efficacy in clinical trials, at least in relapsing disease. Magnetization-transfer, diffusion-weighted MRI, 1H-MRS, and fMRI improve our ability to quantify the pathological changes in MS in vivo. Although we have gained some insight into the disease and are starting to uncover some of the structural and physiological substrates for the disability that develops in MS patients, we are far from understanding what causes MS and how to prevent its progression. Imaging can be used as a tool to better understand the pathophysiology of MS and ultimately improve on the treatment of MS.

Central Nervous System↗
PubMed2004

Sensitivity of the neuroimaging techniques in ischemic stroke.

The aim of this study was to investigate and compare the sensitivity and effectiveness of neuroimaging techniques in 190 patients with acute ischemic stroke. The first computed tomography (CT) scan for all patients was performed within the first 12 hours of the stroke symptoms onset. For each patient, between the third and fifth day of the hospitalization, at least one more neuroimaging procedure (CT and/or magnetic resonance imaging--MRI, and/or diffusion weighted imaging--DWI) was done. The CT scan in the first 12 hours of the stroke onset was positive in 32% of the patients; the highest number of the positive findings was in the patients with total anterior circulation infarct (52%). After 48 hours of the stroke onset second CT was positive in 85% (75/89), MRI in 93.5% (115/123), and DWI in 98.8% (79/80) patients. MRI was significantly more sensitive than CT in detection of ischemic lesion (88% vs. 72%, P=0.01), particularly in the patients with lacunar infarcts (75% vs. 50%, P=0.005). In detection of ischemic stroke 48 hours of the stroke onset the slightly higher number of strokes were detected on DWI in comparison with MRI (98.6% vs. 88.7%). According to our results, within the first 12 hours after the stroke onset, CT is reliable only for detection of considerable number of cortical ischemic strokes of the anterior cerebral circulation. After 48 hours from the stroke onset CT, MRI and DWI show high sensitivity in the detection of ischemic lesion of all clinical stroke subtypes. MRI is more sensitive in comparison with CT in detection of ischemic lesion, while DWI does not show dominance in comparison with MRI in identification of ischemic stroke after 48 hours of the symptoms onset.

Aged↗
PubMed1994

Estimation of the effective self-diffusion tensor from the NMR spin echo.

The diagonal and off-diagonal elements of the effective self-diffusion tensor, Deff, are related to the echo intensity in an NMR spin-echo experiment. This relationship is used to design experiments from which Deff is estimated. This estimate is validated using isotropic and anisotropic media, i.e., water and skeletal muscle. It is shown that significant errors are made in diffusion NMR spectroscopy and imaging of anisotropic skeletal muscle when off-diagonal elements of Deff are ignored, most notably the loss of information needed to determine fiber orientation. Estimation of Deff provides the theoretical basis for a new MRI modality, diffusion tensor imaging, which provides information about tissue microstructure and its physiologic state not contained in scalar quantities such as T1, T2, proton density, or the scalar apparent diffusion constant.

Animals↗
PubMed1999

[A case of medial medullary syndrome detected by diffusion-weighted magnetic resonance imaging].

We report an 84-year-old woman with medial medullary syndrome diagnosed by diffusion-weighted magnetic resonance imaging (MRI). She was admitted because of left hemiparesis and hypesthesia. T2-weighted and diffusion-weighted MRI showed a high signal lesion at the right medial medulla oblongata 10 days after the onset. It is well known that diffusion-weighted MRI is useful for detecting supratentrial cerebral ischemic lesions in the extremely acute stage. However, to our knowledge, there have been only a few reports of diffusion-weighted MRI in patients with ischemic stroke of the medulla oblongata. Normal nerve fibers in the direction perpendicular to the motion-probing gradient (MPG) shows a high signal by diffusion-weighted MRI (anisotropy of apparent diffusion cofficient [ADC]). Normal nerve fibers in the pyramidal tract of medulla oblongata also shows a high signal when the MPG pulse is applied in the x and y directions. We solved this problem by using isotropic diffusion-weighted imaging and were able to detect ischemic lesion of medial medullary infarction in the acute phase.

Aged↗
PubMed2000

[A case of HTLV-I associated myelopathy with abnormal patchy MRI lesions in the spinal cord].

We report a case of HTLV-I associated myelopathy (HAM) with a spinal cord MRI showing abnormal multifocal and patchy lesions. A 50-year-old woman suffering from progressive paraparesis was admitted to our hospital. HTLV-I antibodies in the serum and CSF were positive, and a diagnosis of HAM was made. Her T2 weighted spinal cord MRI showed scattered areas of high signal intensity from the cervical to the thoracic cord. The lesions were enhanced with gadolinium-DTPA on T1 weighted imaging. Atrophy of the thoracic cord has been reported in many patients with HAM. In rare cases, T2 weighed thoracic cord MRI showed diffuse high signal intensity. The pattern of high signal intensity in our case, however, was multifocal and patchy, thus differing from the findings of previous reports. And we believe this is the first such report. This case suggests that the MRI of HAM patient may show multifocal and scattered lesions in the spinal cord.

Biomarkers↗
PubMed2000

[Serum anti-arrestin antibody and disease activity of multiple sclerosis--a case report of 4-year-old child].

We report a 4-year-old girl with multiple sclerosis (MS) and increased serum anti-arrestin antibody. She was admitted to our hospital because of sustained fever, headache and anorexia. Serial magnetic resonance imaging (MRI) revealed diffuse high intensity of cerebral white matter and basal ganglia on T2-weighted imaging. We treated her with high-dose intravenous methylprednisolone under a diagnosis of ADEM. She recovered without any neurological sequelae in three months and the MRI lesion almost disappeared. However, she developed optic neuritis and two episodes of neurologic involvement associated with multiple white matter lesions in the next two years. She was then diagnosed as having clinically definite MS. Anti-arrestin antibody is reportedly present specifically in adult patients with MS and uveitis. We performed an immunoblot assay using bovine retina, and our case revealed the presence of anti-arrestin antibody. Serial examinations showed that the serum anti-arrestin antibody titer correlated well with the disease activity. These results indicate that anti-arrestin antibody may be a good parameter of the disease activity of MS even in childhood.

Arrestin↗
PubMed1993

[Spontaneous cerebrospinal fluid hypotension: value of cerebral MRI].

Spontaneous intracranial hypotension is uncommon. Clinically it consists mainly of postural headache associated with CSF pressure lower than 5 cm H2O. Recently it has been reported that in this syndrome cerebral MRI shows diffuse and symmetrical meningeal enhancement increasing with Gadolinium and disappearing spontaneously without any particular treatment. We report the cases of two women in whom CSF pressure, several weeks after the appearance of headache, was in normal limits and whose cerebral MRI showed such meningeal enhancement. Meningeal biopsy in a search for chronic pachymeningitis was normal in both cases. Diagnosis was established afterwards in the light of recent publications.

Adult↗
PubMed1991

Studies of restricted diffusion in heterogeneous media containing variations in susceptibility.

Measurements of water self-diffusion in heterogeneous media by pulsed gradient spin-echo methods depend on the precise choice of experimental parameters. This variation may reflect the presence of restricted or anisotropic diffusion, or the presence of intrinsic magnetic field gradients. In experiments at 2.0 T, restricted diffusion effects have been demonstrated in freshly excised tissues with an effective barrier radius of order 10 microns. In samples with intrinsic susceptibility variations such as tissues or gels containing dispersions of iron oxide particles, the reduction of apparent diffusion coefficient with diffusion interval can be used to estimate the degree of heterogeneity of the magnetic field in the sample. The implications of these effects for diffusion-weighted MRI as well as their use to derive novel tissue parameters are discussed.

Acrylic Resins↗
PubMed2005

In vivo diffusion tensor imaging (DTI) of brain subdivisions and vocal pathways in songbirds.

The neural substrate for song behavior in songbirds, the song control system (SCS), is thus far the best-documented brain circuit in which to study neuroplasticity and adult neurogenesis. Not only does the volume of the key song control nuclei change in size, but also the density of the connections between them changes as a function of seasonal and hormonal influences. This study explores the potentials of in vivo Diffusion-Tensor MRI (DT-MRI or DTI) to visualize the distinct, concentrated connections of the SCS in the brain of the starling (Sturnus vulgaris). In vivo DTI on starling was performed on a 7T MR system using sagittal and coronal slices. DTI was accomplished with diffusion gradients applied in seven non-collinear directions. Fractional Anisotropy (FA)-maps allowed us to distinguish most of the grey matter and white matter-tracts, including the laminae subdividing the avian telencephalon and the tracts connecting the major song control nuclei (e.g., HVC with RA and X). The FA-maps also allowed us to discern a number of song control, auditory and visual nuclei. Fiber tracking was implemented to illustrate the discrimination of all tracts running from and to RA. Because of the remarkable plasticity inherent to the songbird brain, the successful implementation of DTI in this model could represent a useful tool for the in vivo exploration of fiber degeneration and regeneration and the biological mechanisms involved in brain plasticity.

Algorithms↗