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PubMed2005

Primary central nervous system lymphomas (PCNSL): MRI features at presentation in 100 patients.

To avoid an unnecessary extend of surgery in primary central nervous system lymphoma (PCNSL), the diagnosis should be suspected after MRI. Pre-treatment MRI examinations of 100 immunologically competent patients with biopsy-proven PCNSL were evaluated. All patients had T2- and T1-weighted images with contrast enhancement. Diffusion-weighted MRI (DW-MRI) was available in 15, proton-MR-spectroscopy (1H-MRS) in four patients. The number of lesions ranged from one (n=65 patients) to eight (n=1) with a mean of 1.7. The most frequent locations were the cerebral hemispheres (n=66), the basal ganglia (n=27) and the corpus callosum (n=24). In the 65 patients with a solitary lesion, hemispheric lesions were most frequent (n=23) followed by corpus callosum (n=18). Contrast enhancement was found in all but one patient. 1H-MRS revealed a uniformly pathologic pattern of metabolite concentrations in all patients. Characteristic imaging features of PCNSL are contrast-enhancing lesions with a diameter of at least 15 mm in contact with the subarachnoid space. DW-MRI and proton spectroscopy may aid in differential diagnosis.

Adult↗
PubMed1997

[Principles and clinical applications of diffusion weighted echo planar MR imaging].

The ultrafast capability of echo planar imaging(EPI) made diffusion-weighted MRI (DWI) measurements practical, without the need of head fixation and without the need to exclude patients unable to hold still. The DW hyperintensity and reduced apparent diffusion coefficient(ADC) were observed in all hyperacute strokes, initially at 2.5 hours. In contrast to decreased ADC within 10 days and DW hyperintensity within 30 days, ADC was increased without DW hyperintensity in chronic stage. This suggests that DWI can discriminate between acute and chronic strokes. Furthermore, DWEPI and T2-weighted EPI were also be useful to detect and distinguish acute hemorrhagic stroke from nonhemorrhagic stroke. This review highlighted the promising technique of DWEPI to examine stroke patients in routine clinical practice.

Animals↗
PubMed2003

Cord damage elicits brain functional reorganization after a single episode of myelitis.

OBJECTIVE: To assess, using fMRI, the brain pattern of movement-associated cortical activations in patients with a previous remitting episode of acute cervical myelitis of possible demyelinating origin and to investigate whether the extent of cortical reorganization is associated with the extent of cervical cord pathology measured using magnetization transfer (MT) MRI. METHODS: From 14 right-handed patients in a chronic and stable phase after an isolated myelitis (male/female = 7/7, mean age = 35.3 years, median disease duration = 21.2 months) involving the cervical cord and 15 sex- and age-matched healthy control subjects, we obtained 1) fMRI during repetitive flexion-extension of the last four fingers of the right hand, 2) brain diffusion tensor MRI, and 3) brain and cervical cord conventional and MT MRI. FMRI data were analyzed using Statistical Parametric Mapping software. Brain mean diffusivity, fractional anisotropy, and MT ratio (MTR) histograms of the normal-appearing white and gray matter and cervical cord MTR histograms were produced. RESULTS: Patients with myelitis had lower average cord MTR (p < 0.0001) and cord MTR histogram peak position (p = 0.002) than control subjects. Compared with healthy volunteers, patients with myelitis showed increased recruitment of the ipsilateral hemisphere in the primary sensorimotor cortex (p < 0.0001), supplementary motor area (p = 0.002), and middle frontal gyrus (MFG) (p < 0.0001). Average cervical cord MTR was inversely correlated with relative activations of the ipsilateral MFG (r = -0.80) and of the ipsilateral postcentral gyrus (r = -0.80). The relative activation of the ipsilateral MFG was also correlated with cervical cord MTR peak position (r = -0.92). CONCLUSIONS: An abnormal pattern of movement-associated cortical activations was found in patients with a previous episode of cervical myelitis. These functional cortical changes might have an adaptive role in limiting the clinical outcome of structural cord damage.

Acute Disease↗
PubMed2005

A rigorous framework for diffusion tensor calculus.

In biological tissue, all eigenvalues of the diffusion tensor are assumed to be positive. Calculations in diffusion tensor MRI generally do not take into account this positive definiteness property of the tensor. Here, the space of positive definite tensors is used to construct a framework for diffusion tensor analysis. The method defines a distance function between a pair of tensors and the associated shortest path (geodesic) joining them. From this distance a method for computing tensor means, a new measure of anisotropy, and a method for tensor interpolation are derived. The method is illustrated using simulated and in vivo data.

Anisotropy↗
PubMed2002

Combined diffusion weighting and CSF suppression in functional MRI.

In this study, EPI pulse sequences with diffusion weighting for reduction of contributions from large vessels and inversion pulses in order to minimize the effects of CSF pulsations and CSF partial volume effects were developed for BOLD contrast investigations in functional MR imaging. One inversion recovery echo-planar imaging (IR-EPI) pulse sequence and one IR-EPI with additional diffusion weighting (DW-IR-EPI) were developed and compared to a standard gradient-echo EPI sequence in a cortical stimulation experiment in nine healthy volunteers. Stimulation of motor cortex was performed using a semi-complex finger-tapping paradigm in seven periods of alternating rest and stimulation. Comparison between the three pulse sequences was made by measuring the activated volume in each subject, as well as by calculating the relative signal increase during stimulation. Due to different baseline signal-to-noise levels in the images generated by the three pulse sequences, artificial noise was added so that the comparative investigation could be performed independently of the noise level. The activated volume was 128 +/- 73 pixels (mean +/- SD) using the standard EPI pulse sequence, 31 +/- 12 pixels using IR-EPI and 15 +/- 13 pixels when DW-IR-EPI was employed. The relative signal increase was 5.7 +/- 1.1% using standard EPI, 11.5 +/- 3.1% using IR-EPI and 9.9 +/- 2.4% using DW-IR-EPI. The activated volume obtained with the addition of extra noise, i.e. at equal S/N, was 70 +/- 50 pixels using the standard EPI, and when using IR-EPI, the activated volume was 28 +/- 13 pixels. At equal S/N, the signal increase was 7.3 +/- 1.4% using standard EPI and 12.0 +/- 3.6% using IR-EPI. In BOLD contrast imaging, a combination of diffusion weighting and inversion recovery appeared to reduce false activation caused by CSF pulsation and blood flow in large vessels.

Adult↗
PubMed2005

Three-dimensional muscular architecture of the human tongue determined in vivo with diffusion tensor magnetic resonance imaging.

The myoarchitecture of the tongue is believed to consist of a complex network of interwoven fibers, which function together to produce a near limitless array of functional deformations. These deformations contribute mechanically to speech production and to oral cavity food handling during swallowing. We have previously imaged the 3D myoarchitecture of the mammalian tongue in excised tissue with diffusion tensor MRI, a technique which derives the 3D orientation of intramural fibers as a function of the extent to which a direction-specific MR signal attenuates under diffusion-encoding magnetic gradients. The resulting 3D diffusion tensor defines the relative orientations of the myofiber populations within a region of tissue. In this study, we have extended the use of this method to assess lingual myoarchitecture in normal human subjects in vivo. Subjects were imaged using a diffusion-sensitive stimulated-echo pulse sequence with single-shot echo-planar spatial encoding in the midsagittal plane. Differences in lingual fiber orientation were manifested by graduated changes in fiber direction throughout the tissue, without clear anatomical demarcations between regions of the tissue. The anterior tissue was composed generally of orthogonally oriented fibers surrounded by an axially oriented ring of tissue, whereas the posterior portion of the tissue was composed mostly of fibers projecting in the superior and posterior directions. The bulk of the tissue displayed a highly homogeneous, vertically oriented set of fibers, including the anteroinferior region of the tissue and extending nearly to the superior surface. Further analysis of the tissue in terms of diffusion anisotropy demonstrated that the tissue could be represented by varying degrees of anisotropy, with a tendency toward high anisotropy in the dorsal and anteroventral periphery and low anisotropy in the central region of the tissue. These findings demonstrate that the muscular anatomy of the tongue can be displayed as a continuous array of structural units, or tensors, representing fibers of varying orientations throughout the tissue.

Adult↗
PubMed2006

Structural insights from high-resolution diffusion tensor imaging and tractography of the isolated rat hippocampus.

The hippocampus is a critical structure for learning and memory formation injured by diverse neuropathologies such as epilepsy or Alzheimer's disease. Recently, clinical investigations have attempted to use diffusion tensor MRI as a more specific surrogate marker for hippocampal damage. To first better understand the tissue architecture of healthy hippocampal regions, this study characterized 10 rat hippocampi with diffusion tensor imaging (DTI) at 50-microm in-plane image resolution using a 14.1-T magnet. Chemical fixation of the dissected and straightened rat hippocampus provided a simple, effective way to reduce partial volume effects when segmenting hippocampal regions and improved mean signal-to-noise per unit time (e.g. 50.6+/-4.4 at b=1250 s/mm2 in 27 min). Contrary to previous reports that water diffusion is homogeneous throughout the nervous system, statistically different mean diffusivities were observed (e.g. 0.238+/-0.054 and 0.318+/-0.084 microm2/ms for the molecular and granule cell layers respectively) (ANOVA, P<0.05). Different hippocampal subregions had lower fractional anisotropy than uniformly fibrous structures like corpus callosum because of their complex architecture. DTI-derived color fiber orientation maps and tractography demonstrated most components of the trisynaptic intrahippocampal pathway (e.g. orientations in stratum lacunosum-moleculare were dominated by perforant and Schaffer fibers) and also permitted some assessment of connectivity in the rat hippocampus.

Animals↗
PubMed2006

Comparison of bootstrap approaches for estimation of uncertainties of DTI parameters.

Bootstrap is an empirical non-parametric statistical technique based on data resampling that has been used to quantify uncertainties of diffusion tensor MRI (DTI) parameters, useful in tractography and in assessing DTI methods. The current bootstrap method (repetition bootstrap) used for DTI analysis performs resampling within the data sharing common diffusion gradients, requiring multiple acquisitions for each diffusion gradient. Recently, wild bootstrap was proposed that can be applied without multiple acquisitions. In this paper, two new approaches are introduced called residual bootstrap and repetition bootknife. We show that repetition bootknife corrects for the large bias present in the repetition bootstrap method and, therefore, better estimates the standard errors. Like wild bootstrap, residual bootstrap is applicable to single acquisition scheme, and both are based on regression residuals (called model-based resampling). Residual bootstrap is based on the assumption that non-constant variance of measured diffusion-attenuated signals can be modeled, which is actually the assumption behind the widely used weighted least squares solution of diffusion tensor. The performances of these bootstrap approaches were compared in terms of bias, variance, and overall error of bootstrap-estimated standard error by Monte Carlo simulation. We demonstrate that residual bootstrap has smaller biases and overall errors, which enables estimation of uncertainties with higher accuracy. Understanding the properties of these bootstrap procedures will help us to choose the optimal approach for estimating uncertainties that can benefit hypothesis testing based on DTI parameters, probabilistic fiber tracking, and optimizing DTI methods.

Brain↗
PubMedDate not supplied

Wernicke encephalopathy: unusual findings in nonalcoholic patients.

We report the unique findings on magnetic resonance imaging (MRI) in two cases of diet-related Wernicke encephalopathy (WE). There was no relation to alcohol in either case. The first patient presented with seizures and showed changes of WE on diffusion-weighted MRI with involvement of the motor strip. The second case illustrates extensive changes in the thalamus caused by WE, resulting in obstructive hydrocephalus requiring shunting.

Adult↗
PubMed2001

Diffusion, utilisation and regional variations in the use of CT and MRI in Sweden.

To study the diffusion, access, use, and utilisation of Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) in Sweden a national survey was carried out by a written questionnaire mailed to all public and private hospitals and clinics in 1997. To get a survey of CT and MRI in other countries a request asking for number of units was sent to recognised authorities and individuals in selected countries. CT and MRI were introduced in Sweden in 1973 and 1984 respectively. The diffusion of CT and MRI in Sweden are amongst the highest in the world. Considering the small size of the country and the medical community (e.g. facilitating transparency in indications for use of CT and MRI) and the relatively homogeneous health care system (tax based finance system) the regional variations in access, use, and utilisation of CT and MRI were surprisingly large. For example: In 1996 the number of CT examinations per 100.000 inhabitants varied from 3.344 to 4.705 between the regions. The MRI examinations varied from 751 to 1.858. Some of the differences may be explained by demographic factors. Also, reimbursement policies by the county councils for CT and MRI examinations varied which gave different incentives for patient referrals. However, to explain most of the differences more research is needed. Factors like proportion of elderly amongst the populations in the regions and other socio-demographic factors, proportion of research orientation of examinations and national medical specialities, organisation of the health care, etc. may to a greater extent explain the differences.

Health Services Accessibility↗
PubMed2006

New developments of brain imaging for Parkinson's disease and related disorders.

Parkinson's disease (PD) and related disorders are subcortical degenerations targeting the nigrostriatal dopaminergic system and basal ganglia. Traditionally, MRI has been used to detect structural and positron emission tomography and single emission computed tomography functional neurochemical and metabolic changes associated with these disorders. Recently, advances in diffusion-weighted MRI, ultrasonography, and radiotracer-based imaging have yielded greater sensitivity for revealing structural change and allowed detection of changes in brain dopamine levels after levodopa and during behavioral tasks. This review focuses on these recent advances in neuroimaging technology and their use for the diagnosis and assessment of PD and other parkinsonian disorders.

Blood-Brain Barrier↗
PubMed2001

Topodiagnostic value of blink reflex R1 changes: a digital postprocessing MRI correlation study.

The aim of the study was to investigate the relation of the blink reflex R1 arc to known anatomical brainstem structures. Acute vascular brainstem lesions as identified by magnetic resonance imaging (MRI) of patients with isolated R1 pathology were superimposed into a stereotactic anatomical atlas using a new method of digital postprocessing. Isolated acute brainstem lesions were documented by diffusion-weighted MRI in 12 of 24 patients with unilateral R1 pathology. The lesions were located in the ipsilateral mid- to lower pons. In three patients only, the lesion had partial contact with the principal sensory nucleus of the trigeminal nerve (PSN) on at least one level. In two patients, the lesion involved the medial longitudinal fasciculus. Most lesions were located medially and ventrally to the PSN on transverse slices. Our results underline the high localizing value of changes in the R1 component of the blink reflex in patients with ipsilateral pontine functional deficits. Although available physiological evidence suggests that the R1 component of the blink reflex traverses an oligosynaptic pathway, this MRI study does not support the view that synaptic transmission in the PSN subserves R1. The reflex arc probably descends more medially and ventrally on its course to the facial nucleus.

Adult↗
PubMed2004

[MRI of central nervous system in a series of 58 systemic lupus erythematosus (SLE) patients with or without overt neuropsychiatric manifestations].

PURPOSE: Central nervous (CNS) involvement in SLE is common and can be evaluated with MRI. The primary goal of this study was to evaluate with high-field MRI the CNS involvement in a series of SLE patients with or without neuropsychiatric symptoms. The secondary goal was to detect a possible relationship between MRI and clinical or biological parameters in SLE. MATERIALS AND METHODS: We correlated the clinical and biological parameters of 58 patients with a lupus defined according to the American College of Rheumatology criteria, including 30 with neuropsychiatric manifestations with conventional and modern MRI (including diffusion weighted-images, high-resolution 3D T1 weighted-images). The population studied was compared to a group of 18 normal controls. RESULTS: In 69% of cases, MRI demonstrated involvement of the CNS both in asymptomatic patients (64.3%) and in patients with neuropsychiatric manifestations (73.3%): microembolic signals, cerebral infarctions (associated with the anti-phospholipid syndrome), atrophy, basal ganglia involvement, posterior leucoencephalopathy, subcortical calcification or hemosiderin deposits (T2*), dilated perivascular spaces. CONCLUSION: MRI with adapted sequences clearly demonstrated the cerebral involvement in approximately 70% of SLE patients with or without neuropsychiatric symptoms.

Adult↗
PubMed2003

Functional cortical changes in patients with multiple sclerosis and nonspecific findings on conventional magnetic resonance imaging scans of the brain.

Recent functional magnetic resonance imaging (fMRI) work has suggested that cortical reorganisation might have an adaptive role in limiting the clinical impact of multiple sclerosis (MS) structural damage. In this study, we investigated whether, in patients with MS, the presence and extent of structural damage of the normal-appearing brain tissue are associated with the extent of the movement-associated pattern of cortical activations. Using fMRI and a general search method, we assessed the patterns of brain activations associated with simple motor tasks in 12 right-handed patients with clinically definite MS and nonspecific T2-weighted abnormalities on conventional MRI scans of the brain and compared them with those from 12 sex- and age-matched right- handed healthy controls. Also investigated were the extent to which the fMRI changes correlated with normal-appearing white matter and grey matter (GM) pathology, measured using diffusion tensor MRI. When performing the simple motor task with the dominant hand, MS patients had more significant activations of the ipsilateral supplementary motor area (SMA), the ipsilateral superior frontal sulcus, the contralateral superior temporal gyrus, and the thalamus than controls. On the contrary, healthy subjects showed more significant activations of the medial part of the contralateral parieto-occipital fissure and the ipsilateral primary sensorimotor cortex (SMC) than patients with MS. In patients with MS, the relative activation of the ipsilateral SMA was correlated with the peak height (r = -0.88, P < 0.001) and position (r = 0.87, P < 0.001) of the GM mean diffusivity histogram. This study shows that cortical reorganisation occurs over a rather distributed sensorimotor network even in patients with MS and nonspecific abnormalities on conventional brain MRI scans. This suggests that, in patients with MS, an increased recruitment of movement-associated cortical network can be elicited by the presence of normal-appearing tissue pathology, which is independent of macroscopic T2-weighted abnormalities.

Adult↗
PubMed2003

Magnetic resonance imaging of spinal involvement by hematopoietic malignancies requiring surgical decompression.

To elucidate magnetic resonance imaging (MRI) findings of the spine with hematopoietic malignancies that require surgery, we retrospectively reviewed the MRI scans in these patients who underwent decompression surgery of the spinal cord or cauda equina. Preoperative MRI scans were obtained from nine patients with spinal involvement by a hematopoietic malignancy who underwent surgery: four with malignant lymphoma and five with multiple myeloma. The marrow involvement pattern, location of signal change of the vertebra, cortical destruction, vertebral fracture, epidural mass formation, paraspinal mass formation, and the wrap-around sign (spread to the extraosseous soft tissues without alteration in the shape of the affected vertebra) were determined by MRI scans. Diffuse marrow involvement (89%), anterior and posterior signal changes of the vertebra (100%), cortical destruction (100%), vertebral fracture (78%), epidural mass formation (78%), and paraspinal mass formation (100%) were commonly observed. The wrap-around sign was seen in only one patient (11%); it was due to vertebral destruction and deformity. Based on these results, we concluded that MRI findings of the spine with a hematopoietic malignancy requiring decompression surgery showed a characteristic diffuse marrow pattern; they also exhibited more expansive and destructive features than previously reported for hematopoietic malignancies without surgery.

Aged↗
PubMed2001

Dynamic changes of magnetic resonance imaging abnormalities in relation to inflammation and glial responses after photothrombotic cerebral infarction in the rat brain.

This investigation analyzed the potential of high-resolution magnetic resonance imaging (MRI) at a field strength of 7T to depict leukocyte infiltration and glial responses after focal cerebral ischemia induced by photothrombotic occlusion of cerebral microvessels. For this purpose we superimposed multiparametric MRI (apparent diffusion coefficient, T2, perfusion-weighted, and gadolinium-DTPA-enhanced T1-weighted imaging) on tissue sections stained for phagocytes and astrocytes and, moreover, assessed the regional distribution of tissue pH and ATP content by invasive biochemical methods. Comparing the histological data with the various MRI parameters, high-resolution MRI did not allow a spatial discrimination between distinct areas of phagocyte accumulation or astroglial scar formation, based on image contrast or even quantitative parameter value differences. However, MRI parameters underwent characteristic changes and differentiated distinct stages of tissue remodeling between days 3 and 14 after photothrombosis. Low apparent diffusion coefficient (ADC) and high T2 values indicated an early stage (3 days) with necrosis and beginning glial activation. Normal ADC and reduced T2 elevation characterized an infarct with advanced glial activation and infiltration of hematogenous cells at 7 days after photothrombosis. Heterogeneous ADC together with T2 elevation reflected a late infarct stage (14 days) when pseudocystic degeneration and scar formation had occurred.

Animals↗
PubMed1996

[Infiltration patterns of plasmacytomas in magnetic resonance tomography].

PURPOSE: To define the different infiltration patterns in the spine in multiple myeloma, in correlation with histological and clinical findings. Quantitative signal evaluation with contrast media (Gd-DTPA). To compare the results in MRI with X-ray films. MATERIAL AND METHODS: 61 patients with proven multiple myeloma and 50 controls were examined (1.0 Tesla, T1-w SE, opposed phase GE images). RESULTS: Five infiltration patterns with different clinical stages were detected: normal bone marrow (11%) in cases of low interstitial marrow infiltration (biopsy), pure diffuse infiltration (25%), focal involvement (33%), combined diffuse/focal infiltration (23%) and a "salt-and pepper" pattern (8%). In diffuse plasmacytoma the 40% signal intensity increase was modification of diffuse infiltration. MRI proved to be more sensitive than radiography. CONCLUSION: MRI is able to show the type and the extension of bone marrow infiltration in multiple myeloma. Diffuse involvement can be objective with gadopentetate dimeglumine.

Adult↗
PubMed2004

Cerebral microangiopathy in the mosaic of new discoveries.

After a short historical note on the diversion of the vascular concept of dementia from that of primary degeneration, this review describes cerebral deterioration on vascular grounds in three levels. Occlusions of big vessels with a single major infarct, middle calibre vasculopathy with multiple lacunes and finally microangiopathy causing leukoaraiosis--all these three entities produce cognitive disorders. Changes in the vessel wall, in cerebral blood flow velocity, the territorial and interterritorial rules for the location of malacia or lacunes are reviewed using neuroradiologic aspects revealed by ultrasound, by CT and MRI. Alterations in diffusion and their measurements by MRI are discussed in regard to ultrastructural reactions to ischaemia. Thresholds for tissue deterioration are shown in association with ATP depletion and with pathologic compounds in the interstitium.

Aged↗