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At least 775 records · Page 43Linked to original sources
PubMed2002

MRI of lungs using partial liquid ventilation with water-in-perfluorocarbon emulsions.

A novel (1)H-MRI contrast modality for rat lungs has been developed using water-in-perfluorocarbon (PFC) emulsions for partial liquid ventilation (PLV). The feasibility of the new ventilation protocol for (1)H-MRI studies of lungs has been demonstrated. (1)H-MR images of lungs have been obtained with sensitivity and spatial resolution higher than those of the (19)F-MRI of lungs previously reported. Diffusion-weighted MRI measurements of lungs showed that the results obtained are related to the pulmonary architecture and functional properties of lungs. Although the methodology needs further improvement and evaluation, it appears to have great potential in a wide range of new applications in the field of lung MRI, such as in vivo detection of lung cancer, emphysema, and allograft rejection following lung transplantation. The ability of this technique to achieve high-quality MR images of lungs, together with its technical simplicity, stability, and low cost, makes this method a promising imaging technique for the lungs.

Animals↗
PubMed2003

Neuro-Behçet's disease: analysis of apparent diffusion coefficients.

Little is known about the diffusion properties of brain lesions in neuro-Behçet's disease (NBD). We looked at 19 NBD lesions (13 active, six chronic) in six patients, using diffusion-weighted MRI (DWI). We calculated the apparent diffusion coefficients (ADC) of the lesions and compared them with normal contralateral brain, expressing this ratio as relative ADC (rADC). The rADC was 1.29+/-0.33 in active and 1.44+/-0.47 in chronic lesions, i.e., significantly higher than in the control regions. Increased diffusivity in both active and chronic phases in NBD is different from the pattern in ischaemic infarcts, so that ADC analysis might be helpful for differentiating between these conditions.

Adolescent↗
PubMed2002

Delayed onset of brain edema and mislocalization of aquaporin-4 in dystrophin-null transgenic mice.

Cerebral water accumulation was studied during induction of brain edema in dystrophin-null transgenic mice (mdx-betageo) and control mice. Immunofluorescence and immunoelectron microscopic analyses of dystrophin-null brains revealed a dramatic reduction of AQP4 (aquaporin-4) in astroglial end-feet surrounding capillaries (blood-brain barrier) and at the glia limitans (cerebrospinal fluid-brain interface). The AQP4 protein is mislocalized, because immunoblotting showed that the total AQP4 protein abundance was unaltered. Brain edema was induced by i.p. injection of distilled water and 8-deamino-arginine vasopressin. Changes in cerebral water compartments were assessed by diffusion-weighted MRI with determination of the apparent diffusion coefficient (ADC). In dystrophin-null mice and control mice, ADC gradually decreased by 5-6% from baseline levels during the first 35 min, indicating the initial phase of intracellular water accumulation is similar in the two groups. At this point, the control mice sustained an abrupt, rapid decline in ADC to 58% +/- 2.2% of the baseline at 52.5 min, and all of the animals were dead by 56 min. After a consistent delay, the dystrophin-null mice sustained a similar decline in ADC to 55% +/- 3.4% at 66.5 min, when all of the mice were dead. These results demonstrate that dystrophin is necessary for polarized distribution of AQP4 protein in brain where facilitated movements of water occur across the blood-brain barrier and cerebrospinal fluid-brain interface. Moreover, these results predict that interference with the subcellular localization of AQP4 may have therapeutic potential for delaying the onset of impending brain edema.

Animals↗
PubMed2002

Symptomatic vasospasm after subarachnoid haemorrhage: assessment of brain damage by diffusion and perfusion-weighted MRI and single-photon emission computed tomography.

Our purpose was to assess the usefulness of diffusion- and perfusion-weighted MRI for the detection of ischaemic brain damage in patients with suspected vasospasm after subarachnoid haemorrhage (SAH). We studied 11 patients admitted with a ruptured aneurysm of the anterior circulation and suspected of intracranial vasospasm on clinical examination and transcranial Doppler sonography (TCD). All were investigated by technetium-hexamethyl-propylene amine oxime (Tc-HMPAO) single photon emission computed tomography (SPECT) and diffusion and perfusion-weighted MRI (DWI, PWI) within 2 weeks of their SAH. Trace images and TTP maps were interpreted by two examiners and compared with clinical and imaging follow-up. PWI revealed an area of slowed flow in seven patients, including four with major and three with minor hypoperfusion on SPECT. In two patients, PWI did not demonstrate any abnormality, while SPECT revealed major hypoperfusion in one and a minor deficit hypoperfusion in the other. Two patients with high signal on DWI had a permanent neurological deficit.

Adult↗
PubMed1999

ADC mapping by means of a single-shot spiral MRI technique with application in acute cerebral ischemia.

Diffusion-weighted MRI based on single-shot echo planar imaging (EPI) has been established as a useful tool to study acute cerebral ischemia. However, EPI is prone to spatial distortion and ghosting artifacts. In this study, a pulse sequence for diffusion-weighted imaging (DWI) based on a single-shot spiral readout is presented. Using this technique, multislice apparent diffusion coefficient (ADC) mapping can be performed in an interleaved fashion with the same temporal resolution as EPI. Other advantages associated with ADC mapping by the single-shot spiral method include minimal ghosting artifacts, reduced spatial distortion, and capability to scan in arbitrary planes. This technique has been successfully tested in five normal volunteers and three stroke patients. It has been demonstrated that the single-shot spiral technique is capable of producing high quality DWI and ADC trace maps (128 x 128) in the axial, sagittal, and coronal planes, which facilitate clinical diagnosis.

Acute Disease↗
PubMed2000

Diffusion- and T2-weighted MRI of the transverse pontine fibres in spinocerebellar degeneration.

Because the transverse pontine fibres degenerate in some subtypes of spinocerebellar degeneration (SCD), demonstration of these fibres may be helpful for radiological diagnosis of SCD. Using multishot diffusion-weighted MRI, we attempted to find a way to show the transverse pontine fibres. We assessed the quality of demonstration of these fibres on DWI and of abnormal high signal in the pons and middle cerebellar peduncles on T2-weighted images. We examined evaluated 24 control subjects and 12 patients with SCD: two with sporadic olivopontocerebellar atrophy (OPCA), five with spinocerebellar ataxia type 1 (SCA1), two with SCA3, and three with SCA6. In all control subjects and patients with SCA6, we succeeded in demonstrating the transverse pontine fibres as clear low-signal bundles using DWI. In two patients with SCA3, these fibres were identified less distinctly. In contrast, in two patients with sporadic OPCA and in four of five patients with SCA1, the fibres were not identified. In both patients with sporadic OPCA, abnormal high-signal foci were seen in the base of the pons and middle cerebellar peduncles on T2-weighted images; no such foci were detected in any patient with SCA1, SCA3 or SCA6. DWI seems to be useful for demonstrating transverse pontine fibres. Abnormal high signal in the pons and middle cerebellar peduncles may provide a clue to differentiation of sporadic OPCA from other types of SCD.

Adult↗
PubMed2000

The measurement of diffusion and perfusion in biological systems using magnetic resonance imaging.

The aim of this review is to describe two recent developments in the use of magnetic resonance imaging (MRI) in the study of biological systems: diffusion and perfusion MRI. Diffusion MRI measures the molecular mobility of water in tissue, while perfusion MRI measures the rate at which blood is delivered to tissue. Therefore, both these techniques measure quantities which have direct physiological relevance. It is shown that diffusion in biological systems is a complex phenomenon, influenced directly by tissue microstructure, and that its measurement can provide a large amount of information about the organization of this structure in normal and diseased tissue. Perfusion reflects the delivery of essential nutrients to tissue, and so is directly related to its status. The concepts behind the techniques are explained, and the theoretical models that are used to convert MRI data to quantitative physical parameters are outlined. Examples of current applications of diffusion and perfusion MRI are given. In particular, the use of the techniques to study the pathophysiology of cerebral ischaemia/stroke is described. It is hoped that the biophysical insights provided by this approach will help to define the mechanisms of cell damage and allow evaluation of therapies aimed at reducing this damage.

Animals↗
PubMed2002

[Acute cerebral infarction--diagnosis of subgroups].

BACKGROUND: Subclassification of cerebral infarcts is crucial in order to optimise and differentiate therapy. If we are to apply specific treatment modalities early while neurological deficits are still reversible, we need a fast diagnosis that reliably predicts etiology. MATERIAL AND METHODS: The early clinical classification into Oxford subgroups is presented with an assessment of their predictive value in relation to aetiology (TOAST classification). RESULTS: The various Oxford subgroups correlate well to the topography of the infarction demonstrated by neuroradiology, to the vascular aetiology as demonstrated by ultrasound techniques, and to the "aetiologic" subgroup as determined by a full diagnostic work-up. However, the correlation is not sufficient to guide potentially specific treatments of subgroups if the treatment in question has serious side effects (e.g. thrombolysis). However, if the clinical diagnosis is supplemented with diffusion-weighted MRI and perhaps MR angiography, the predictive value of the diagnosis is extremely high. INTERPRETATION: Very early clinical diagnosis of cerebral infarction must be supplemented with diffusion-weighted MRI to make the diagnostic precision sufficiently high to guide the application of specific treatments with potentially serious side effects.

Acute Disease↗
PubMed2005

Diffusion tensor imaging using partial Fourier STEAM MRI with projection onto convex subsets reconstruction.

Diffusion-weighted single-shot STEAM MRI allows for diffusion mapping of the human brain without sensitivity to resonance offset effects. In order to compensate for its inherently lower SNR and speed than echo-planar imaging, this work describes the use of partial Fourier encoding in combination with image reconstruction by the projection onto convex subsets algorithm. The method overcomes phase distortions in diffusion-weighted partial Fourier acquisitions that disturb the conjugate complex symmetry of k-space and preclude the use of respective reconstruction techniques. In comparison with full Fourier encoding and a static flip angle for the STEAM readout pulses, experimental results at 2.9 T demonstrate a gain in relative SNR per unit time by 20% for 5/8 phase encoding with optimized variable flip angles. Simultaneously, the imaging time is reduced from about 670 ms (80 echoes) to 440 ms (50 echoes). Current implementations at 2 x 2 mm2 in-plane resolution comprise a protocol for clinical anisotropy studies (12 diffusion-encoding gradient directions at 1000 s mm(-2)) covering 18 sections of 4-mm thickness within a measurement time of 8.5 min (5 averages) and a version optimized for fiber tracking using 24 gradient directions and 38 sections of 2-mm thickness yielding a measurement time of 29.5 min (4 averages).

Anisotropy↗
PubMed2004

Silent embolism in diagnostic cerebral angiography: detection with diffusion-weighted imaging.

Angiography has known and documented risks of neurological events. We prospectively studied 20 patients who underwent diagnostic cerebral angiographic examinations and diffusion-weighted MRI (DWI). Eighteen patients had DWI before and after their angiogram, whereas two patients had a DWI only after their angiogram (DWI was normal in both of these patients). No clinical neurological deficits were detected in any of our patients after angiography, but in three of 20 patients there was a new hyperintense signal abnormality found on DWI. Diffusion-weighted MRI provides an objective means of detecting both clinical and subclinical neurological events. Diffusion-weighted imaging might therefore provide an easier method of assessing complication rates in cerebral angiography by reducing the number of patients required for meaningful statistical analysis.

Adult↗
PubMed1997

Reversible MRI findings in a patient with Hashimoto's encephalopathy.

Diffuse subcortical MRI signal abnormalities were seen during a subacute exacerbation in a patient with Hashimoto's encephalopathy. The patient had an excellent clinical response to corticosteroids. Clinical recovery paralleled normalization of MRI abnormalities and lowering of thyroid microsomal antibody titer.

Aged↗
PubMed1997

Increased water diffusion in cerebral white matter in Alzheimer's disease.

We investigated the changes in water diffusion in the cerebral white matter in 19 patients with Alzheimer's disease (AD), including 11 without and 8 with periventricular hyperintensity (PVH) lesions, using diffusion-weighted magnetic resonance imaging (MRI). The apparent diffusion coefficients in the anterior and posterior white matter were significantly higher in the 19 AD patients than in the 10 age-matched controls. The apparent diffusion coefficients were higher in patients with PVH than in those without. The anisotropic ratios, defined as diffusion restricted perpendicular to the direction of the nerve fibers, were significantly higher in AD patients, even in those without PVH, than in the controls. Our results suggest that mild myelin loss occurs in AD patients even in the apparently normal white matter. A definite loss of myelin and axons, including incomplete infarction, occurs in the white matter, as seen on T2-weighted images as PVH. Studies with diffusion-weighted MRI may allow the characterization of different pathological processes and enable the demonstration of underlying white matter lesions in AD that cannot be visualized by conventional MRI.

Aged↗
PubMedDate not supplied

Brain abscess and cystic brain tumor: discrimination with dynamic susceptibility contrast perfusion-weighted MRI.

Differentiating between brain abscesses and cystic brain tumors such as high-grade gliomas and metastases is often difficult with conventional MRI. The goal of this study was to evaluate the diagnostic utility of perfusion MRI to differentiate between these pathologies. MRI was performed in 19 patients with rim-enhancing brain lesions (4 pyogenic abscesses, 8 high-grade gliomas, 7 metastases). In addition to standard MR sequences, trace diffusion-weighted MRI with apparent diffusion coefficient (ADC) maps and perfusion-weighted MRI by using a first-pass gadopentetate dimeglumine T2*-weighted gradient echo single-shot echo-planar sequence were performed. Relative cerebral blood volume (rCBV) ratios were obtained via the values of the capsular portions of the lesions and the normal white matter. All the abscesses had markedly hyperintense signals in trace diffusion images, whereas they had significant hypointense signals in ADC images. In perfusion-weighted images, the capsular portions of the abscesses demonstrated low colored areas compared with the normal white matter and the rCBV ratio calculated was 0.76 +/- 0.12 (mean +/- SD). All but two of the cystic tumors showed low signal intensity on trace diffusion-weighted images and high signal intensity on ADC maps. Hyperintense signal was found in two brain tumors mimicking brain abscesses on trace diffusion images. The rCBV values in high-grade gliomas and metastases were 5.51 +/- 2.08 and 4.58 +/- 2.19, respectively. The difference between abscesses and cystic tumors was statistically significant (P = 0.003). Perfusion MRI may allow the differentiation of pyogenic brain abscess from cystic brain tumors, making it a strong additional imaging modality in the early diagnosis of these two entities.

Adolescent↗
PubMed2006

[Neuroimaging findings in eclamptic patients still symptomatic after 24 hours: a descriptive study about 19 cases].

OBJECTIVE: To describe the neuroimaging findings in eclamptic patients still symptomatic after 24 hours. PATIENTS AND METHODS: All parturients consecutively admitted over a 12-month period for eclampsia and presenting with neurological disorders (coma, focal neurological abnormalities, and eye sight disturbance) underwent cerebral CT-scan and/or MRI. RESULTS: Nineteen women were studied, and all had abnormal neuroradiological findings. The CT-scan was normal in three cases. Cerebral oedema was the predominant lesion (14 cases). It was localized in the parietal or occipital area (12 cases), paraventricular area (1 case), or was diffuse (1 case). Diffusion weighted MRI was performed in four cases and showed cytotoxic cerebral oedema in one case. There were three cases of cerebral venous thrombosis and two cases of intracerebral haemorrhage. CONCLUSION: Various neuroradiological lesions can be observed in eclamptic patients. A localized cerebral oedema is the most frequent. Diffusion weighted MRI should be systematically done when neurological disorders persist.

Adolescent↗
PubMed1994

Spinal epidural abscess with gadolinium-enhanced MRI: serial follow-up studies and clinical correlations.

We reviewed serial MRI with and without gadolinium-DTPA in eight patients with spinal epidural abscess and correlated the findings and the clinical manifestations. In four patients, diffuse abscesses spanned four vertebral bodies or more; the others had focal abscesses associated with osteomyelitis and/or diskitis. In three of the four patients with diffuse abscesses, MRI (NCMRI) showed diffuse encasement of the subarachnoid space. Contrast-enhanced MRI (CEMRI) demonstrated linear enhancement surrounding unenhanced pus. In the four patients with focal abscesses, CEMR delineated the inflammatory process more clearly than NCMR. On follow-up studies, decrease in abscess size and better visualization of the subarachnoid space correlated with clinical improvement in both diffuse and focal abscesses. Despite clinical improvement, contrast enhancement persisted in the disk or epidural space of three patients, and was thought to represent chronic granulomatous change or postsurgical scar. CEMR is very valuable for the initial diagnosis of an epidural abscess, particularly if it involves lengthy segments. During follow-up, CEMR can document responses to therapy, and provide information for determining appropriate treatment.

Abscess↗
PubMed2001

The Heidenhain variant of Creutzfeldt-Jakob disease: clinical, pathologic, and neuroimaging findings.

We report two patients who developed isolated visual symptoms and signs as initial manifestations of Creutzfeldt-Jakob disease (CJD). Both patients had normal conventional T1- and T2-weighted brain magnetic resonance (MR) images; in one patient, early cortical abnormalities were detected by diffusion-weighted and fluid attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI). Results from the cerebrospinal fluid assay for the 14-3-3 brain protein were also negative in one patient, despite pathologic confirmation of CJD at autopsy. The Heidenhain variant of CJD should be considered in all patients who present with isolated visual manifestations, including homonymous hemianopsia and normal conventional brain MRI. Diffusion-weighted and FLAIR MRI may demonstrate early cortical abnormalities in patients with CJD. The CSF assay for the 14-3-3 protein may be normal, even in pathologically confirmed cases.

14-3-3 Proteins↗
PubMed2004

Diffusion-weighted imaging of intravascular clots in cerebral venous thrombosis.

BACKGROUND AND PURPOSE: Hyperintensities on diffusion-weighted MRI at the site of venous occlusion have previously been reported in cerebral venous thrombosis (CVT). The frequency of these signal changes according to late venous recanalization was not determined yet. METHODS: In a series of 28 patients with recent CVT, the frequency of hyperintense signals as seen on diffusion-weighted MRI in vein(s) or sinus(es) (HSVdwi) was assessed at the time of diagnosis, as was rate of recanalization 2 to 3 months after anticoagulation. RESULTS: HSVdwi was detected in 20 occluded vein(s) or sinus(es) in 12 patients (41%) with recent CVT. The mean apparent diffusion coefficient measured in 5 patients within HSVdwi in the superior sagittal sinus was 4.88+/-1.49x10-4mm2/s. The delay since clinical onset was larger in the presence than in the absence of HSVdwi as detected at the time of diagnosis. No HSVdwi was visible at the second MRI although some vessels remained occluded. Complete recanalization of the vessel was less frequent when HSVdwi was observed on the first MRI (35% versus 88%, P=0.005). CONCLUSIONS: Results of this study suggest that the movements of water molecules are more or less restricted within the venous clot according to the stage of thrombus formation in CVT. The presence of HSVdwi in occluded veins at the time of diagnosis might be predictive of a low rate of vessel recanalization 2 or 3 months later.

Adolescent↗
PubMed2002

A continuous tensor field approximation of discrete DT-MRI data for extracting microstructural and architectural features of tissue.

The effective diffusion tensor of water, D, measured by diffusion tensor MRI (DT-MRI), is inherently a discrete, noisy, voxel-averaged sample of an underlying macroscopic effective diffusion tensor field, D(x). Within fibrous tissues this field is presumed to be continuous and smooth at a gross anatomical length scale. Here a new, general mathematical framework is proposed that uses measured DT-MRI data to produce a continuous approximation to D(x). One essential finding is that the continuous tensor field representation can be constructed by repeatedly performing one-dimensional B-spline transforms of the DT-MRI data. The fidelity and noise-immunity of this approximation are tested using a set of synthetically generated tensor fields to which background noise is added via Monte Carlo methods. Generally, these tensor field templates are reproduced faithfully except at boundaries where diffusion properties change discontinuously or where the tensor field is not microscopically homogeneous. Away from such regions, the tensor field approximation does not introduce bias in useful DT-MRI parameters, such as Trace(D(x)). It also facilitates the calculation of several new parameters, particularly differential quantities obtained from the tensor of spatial gradients of D(x). As an example, we show that they can identify tissue boundaries across which diffusion properties change rapidly using in vivo human brain data. One important application of this methodology is to improve the reliability and robustness of DT-MRI fiber tractography.

Anisotropy↗