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PubMed2001

Detection of hyperacute parenchymal hemorrhage of the brain using echo-planar T2*-weighted and diffusion-weighted MRI.

We investigated the usefulness of echo-planar imaging (EPI) as well as T2*-weighted and diffusion-weighted MRI (DWI) to identify hyperacute hemorrhage (within 24 h after ictus) in the brain. Seven patients were examined 3.5 to 24 h after onset of symptoms using a whole-body 1.5-T MR system. Two diffusion-weighted sequences were run to obtain isotropic and anisotropic diffusion images. Apparent diffusion coefficients (ADC) were calculated from the isotropic diffusion images. All DWI images as well as the T2*-weighted EPI images showed the hematomas as either discrete, deeply hypointense homogeneous lesions, or as lesions of mixed signal intensity containing hypointense areas. We conclude that even in the early phase after hemorrhage, sufficient amounts of paramagnetic deoxyhemoglobin are present in intracerebral hemorrhages to cause hypointensity on EPI T2*-weighted and DWI images; thus, use of ultrafast EPI allows identification of intracerebral hemorrhage.

Acute Disease↗
PubMed1999

[Magnetic resonance tomography in stroke--its methodological bases and clinical use].

Stroke is the third leading cause of death. Until recently, no diagnostic technique was available that could reliably depict ischemic tissue within a therapeutically promising time window. Since the beginning of this decade, a fundamental change has taken place: Perfusion- and diffusion-MRI have shown to be capable of depicting the ischemic injury immediately after vessel occlusion. While perfusion MRI is sensitive to abnormalities in cerebral capillary blood flow (micro-circulation), diffusion MRI indicates tissue damage on a cellular level. Combining perfusion- and diffusion-MRI with standard MR technique (T2-weighted sequences, MR angiography) results in an MR protocol that is complementary and gives insight into both structural and functional parameters.

Artifacts↗
PubMed2006

Value of diffusion-weighted MRI during carotid angioplasty and stenting.

INTRODUCTION: The incidence of neurological injury following carotid angioplasty and stenting is of great interest to those advocating it as an alternative to endarterectomy in the management of critical carotid stenosis. A significant inter-observer variation exists in determining the presence or absence of a neurological deficit following the procedure objective imaging would be advantageous. In this study, we sought to assess diffusion weighted MRI as a diagnostic tool in evaluating the incidence of neurological injury following carotid angioplasty and stenting (CAS). PATIENTS AND METHODS: The first 110 cases of CAS in our unit were included in this series. The procedure was abandoned in three patients. Patients underwent intracranial and extracranial MR angiography, together with diffusion-weighted MRI (DWI) prior to and following CAS and had a formal neurological assessment in the intensive care unit after the procedure. RESULTS: One hundred and ten Procedures were attempted in 98 patients. Twenty-eight percent were asymptomatic. Following CAS, 7.2% of patients had a positive neurological exam (two major strokes with one fatality) and 21% had positive DWI scans, equating to a sensitivity of 86% and a specificity of 85% for DWI in detecting cerebral infarction following CAS. The positive predictive value of the test was 0.3 and negative predictive value 0.99. The major stroke and death rate was 1.8%. While the use of a cerebral protection device appeared to significantly reduce the incidence of cerebral infarction (5% vs. 25%, p = 0.031) this may be a reflection of the learning curve encountered during the study. CONCLUSION: The incidence of subclinical DWI detected neurological injury was significantly higher than clinical neurological deficit following CAS. Conventional methods of neurological assessment of patients undergoing CAS may be too crude to detect subtle changes and more sensitive tests of cerebral function are required to establish whether these subclinical lesions are relevant.

Aged↗
PubMed1998

Diffusion-weighted MRI characterizes the ischemic lesion in transient global amnesia.

We present a patient with transient global amnesia (TGA) whose diffusion-weighted MRI (DWI) showed increased signal in the splenium of the corpus callosum and in the left parahippocampal gyrus. The absence of high signal on the corresponding apparent diffusion coefficient (ADC) images supports the diagnosis of an acute infarction. This finding provides a temporal relation between cerebral ischemia and infarction in the territory of posterior cerebral artery and in certain cases of TGA. An early means of detecting ischemia in TGA by DWI may influence clinical decisions made in patient evaluation and management.

Amnesia↗
PubMed2001

Two-component diffusion tensor MRI of isolated perfused hearts.

Nonmonoexponential MR diffusion decay behavior has been observed at high diffusion-weighting strengths for cell aggregates and tissues, including the myocardium; however, implications for myocardial MR diffusion tensor imaging are largely unknown. In this study, a slow-exchange-limit, two-component diffusion tensor model was fitted to diffusion-weighted images obtained in isolated, perfused rat hearts. Results indicate that there are at least two distinct components of anisotropic diffusion, characterized by a "fast" component whose principal diffusivity is comparable to that of the perfusate, and a highly anisotropic "slow" component. It is speculated that the two components correspond to tissue compartments and have a general agreement with the orientations of anisotropy, or fiber orientations, in the myocardium. Moreover, consideration of previous studies of myocardial diffusion suggests that the presently observed fast component may likely be dominated by diffusion in the vascular space, whereas the slow component may include the intracellular and interstitial compartments. The implications of the results for myocardial fiber orientation mapping and limitations of the current two-component model used are also discussed.

Animals↗
PubMed1998

Diffusion-weighted MRI for evaluation of acute stroke.

Diffusion-weighted imaging (DWI) is a new magnetic resonance imaging technique that detects the tiny random movements of water molecules (diffusion) in tissues. This technique allows a map of the average apparent diffusion coefficient (ADC) to be calculated. Shortly after the onset of an ischemic stroke, the ADC of brain tissue is significantly reduced because of cytotoxic edema. Over several days, the rapid initial drop in ADC is followed by a return to "pseudonormal" values at approximately 1 week. Subsequently, elevated ADC values are seen at chronic time points. DWI is remarkably sensitive in detecting and localizing acute ischemic brain lesions and allows differentiation of acute regions of ischemia from chronic infarcts. Recent studies have shown a high correlation between the volume of early DWI lesions and clinical neurologic outcome. In addition, the volume of the early DWI lesion correlates well with final infarct volume as measured by T2-weighted imaging. Therefore, this technique may facilitate optimal selection of patients for new medical therapies for stroke and may provide a highly sensitive technique for evaluating the efficacy of new treatments.

Acute Disease↗
PubMed2003

[Diffusion tensor MRI of Wallerian degeneration: a case report].

Diffusion tensor imaging allows a 3D analysis of water molecular motion and an exploration of white matter tracts integrity and orientation. We report a diffusion tensor study of wallerian degeneration of the corticospinal tract following a capsulo-lenticular hemorrhage in a 49-year old man. Reduced anisotropy (loss of fiber coherence) with preserved diffusivity of the damaged corticospinal tract was observed. This highlights the feasibility of diffusion tensor imaging on clinical MR units and its ability to quantify the degree of white matter tract destruction.

Anisotropy↗
PubMed2006

Serial diffusion tensor MRI after transient and permanent cerebral ischemia in nonhuman primates.

BACKGROUND AND PURPOSE: We measured the temporal evolution of the T2 and diffusion tensor imaging parameters after transient and permanent cerebral middle cerebral artery occlusion (MCAo) in macaques, and compared it to standard histological analysis at the study end point. METHODS: Stroke was created in adult male macaques by occluding a middle cerebral artery branch for 3 hours (transient MCAo, n=4 or permanent occlusion, n=3). Conventional MRI and diffusion tensor imaging scans were performed 0 (acute day), 1, 3, 7, 10, 17, and 30 days after MCAo. Animals were euthanized after the final scan and the brains removed for histological analysis. RESULTS: Apparent diffusion coefficient in the lesion was decreased acutely, fractional anisotropy was elevated, and T2 remained normal. Thereafter, apparent diffusion coefficient increased above normal, fractional anisotropy decreased to below normal, T2 increased to a maximum and then declined. Reperfusion at 3 hours accelerated these MRI changes. Only the fractional anisotropy value was significantly different between transient and permanent groups at 30 days. Final MRI-defined fractional lesion volumes were well correlated with corresponding histological lesion volumes. Permanent MCAO animals showed more severe histological damage than their transient MCAO counterparts, especially myelin damage and axonal swelling. CONCLUSIONS: Overall, the MRI evolution of stroke in macaques was closer to what has been observed in humans than in rodent models. This work supports the use of serial MRI in stroke studies in nonhuman primates.

Animals↗
PubMed2004

Diffusion-weighted MRI abnormalities as an early diagnostic marker for Creutzfeldt-Jakob disease.

OBJECTIVE: To evaluate the usefulness of diffusion-weighted MRI (DWI) for the early diagnosis of Creutzfeldt-Jakob disease (CJD). METHODS: Thirty-six consecutive patients (age 56 to 82 years) were enrolled, and 26 were examined by DWI. Nine were definite based on the World Health Organization criteria, and 27 were probable. The percentages of DWI abnormalities, periodic sharp wave complexes (PSWCs) on the EEG, detection of CSF 14-3-3 protein, and increase of CSF neuron-specific enolase (>25 ng/mL) on the first examination were compared. For DWI, 32 patients (age 31 to 84 years) who showed progressive dementia or impaired consciousness served as disease controls. RESULTS: The percentage of DWI abnormalities was 92.3%, of PSWCs 50.0%, of 14-3-3 protein detection 84.0%, and of NSE increase 73.3%. Two of the 32 control subjects were falsely positive on DWI. The sensitivity of DWI was 92.3% (95% CI 74.8 to 99.5%) and specificity 93.8% (95% CI 79.2 to 99.2%). In 17 patients who did not show PSWCs on the first EEG, abnormal DWI findings were still clearly detected. Four patients who were negative for 14-3-3 protein also showed DWI abnormalities. DWI abnormalities were detected as early as at 3 weeks of symptom duration in four patients in whom PSWCs were not yet evident. CONCLUSIONS: DWI can detect characteristic lesions in the majority of patients with CJD regardless of the presence of PSWCs. DWI was the most sensitive test for the early clinical diagnosis of CJD; consideration should be given to its inclusion in the clinical diagnostic criteria of CJD.

14-3-3 Proteins↗
PubMed2003

Wernicke's encephalopathy: is diffusion-weighted MRI useful?

We present the clinical and magnetic resonance imaging (MRI) findings of five patients with acute Wernicke's encephalopathy. T2-weighted and fluid-attenuated inversion recovery (FLAIR) images demonstrated symmetrical hyperintense lesions within the dorsomedial thalami, periaqueductal white matter, and the tectum of the midbrain. None of the lesions enhanced with gadolinium. In addition to conventional MRI sequences, we performed diffusion-weighted imaging (DWI). In all patients, DWI showed symmetrical pathologic thalamic and midbrain signal hyperintensities more distinctly than did conventional T2-weighted or FLAIR sequences. The apparent diffusion coefficient (ADC) map images showed slight signal reductions in four patients, suggesting restricted diffusion within these regions. In one patient, the signal intensity within the affected thalami was isointense with the ipsilateral basal ganglia on ADC map images. For enhanced detection of pathology, we conclude that DWI should be included in the imaging protocols of patients suspected to suffer from Wernicke's encephalopathy.

Acute Disease↗
PubMed2004

Magnetization transfer and diffusion tensor MRI show gray matter damage in neuromyelitis optica.

Using magnetization transfer (MT) and diffusion tensor (DT) MRI, the authors assessed the extent of tissue damage of the brain normal-appearing white and gray matter (NAGM) in patients with neuromyelitis optica (NMO). Compared to healthy controls, patients with NMO showed reduced MT ratio and increased mean diffusivity of the NAGM. This challenges the classic notion of a sparing of the brain tissue in the course of NMO.

Adult↗
PubMedDate not supplied

Case report: diffusion-weighted MRI in anterior spinal artery stroke of the cervical spinal cord.

The authors present a case of anterior spinal artery stroke demonstrated by diffusion-weighted MRI (DWI) using single-shot echo-planar imaging. DWI clearly demonstrated hyperintensity with a decreased apparent diffusion coefficient (ADC) at 26 hours after onset. At 28 days, there was persistent hyperintensity with an increased ADC, corresponding to T2-weighted hyperintensity in the whole spinal gray matter at the C2-C7 vertebral level. DWI provided satisfactory images and was helpful for diagnosing and evaluating anterior spinal artery stroke.

Anterior Spinal Artery Syndrome↗
PubMed2002

Diffusion-weighted MRI of maple syrup urine disease encephalopathy.

We report the case of a newborn child with maple syrup urine disease (MSUD), diagnosed at 10 days of life. Diffusion-weighted echoplanar MRI showed marked hyperintensity of the cerebellar white matter, the brainstem, the cerebral peduncles, the thalami, the dorsal limb of the internal capsule and the centrum semiovale, while conventional dual-echo sequence evidenced only a weak diffuse T2 hyperintensity in the cerebellar white matter and in the dorsal brainstem. The apparent diffusion coefficient (ADC) of these regions was markedly (>80%) decreased. Therefore, in agreement with current hypotheses on MSUD pathogenesis, MSUD oedema proves to be a cytotoxic oedema. Diffusion-weighted MRI may be a valuable tool, more sensitive than conventional spin-echo techniques, to assess the extent and progression of cytotoxicity in MSUD, as well as the effectiveness of the therapeutic interventions.

Diffusion↗
PubMed1993

The influence of health technology assessment on the diffusion of MRI in Australia.

A major assessment of magnetic resonance imaging (MRI) in Australia influenced the early use of this technology and informed policy decisions on future MRI services. However, the impact of the assessment, and of government policy, on the subsequent diffusion of MRI has been more modest, reflecting the limitations of the evaluation process in a complex health care system.

Australia↗
PubMed2006

High-B-value diffusion-weighted MRI in colorectal cancer.

OBJECTIVE: The purpose of this article is to evaluate the usefulness of high-b-value diffusion-weighted MRI (DW-MRI) in the detection of colorectal adenocarcinoma. CONCLUSION: High-b-value DW-MRI allows detection of colorectal adenocarcinoma with a high sensitivity and specificity.

Adenocarcinoma↗
PubMed2000

[Diffusion-weighted MRI in patients with Creutzfeldt-Jakob disease].

Today the diagnosis of Creutzfeldt-Jakob disease (CJD) is proven only postmortem or by evidence of neuropathology. During the patient's lifetime EEG recordings or cerebrospinal fluid analysis may support the diagnosis. In most cases, T2-MRI scans show hyperintensities of the basal ganglia. A new imaging technique called diffusion-weighted MRI (DWI) has recently been established. The sensitivity of DWI was evaluated in five patients suspected of CJD. All five cases showed hyperintense signal changes in the basal ganglia on DWI sequences. These findings were more pronounced in DWI than in T2, FLAIR, or PD-weighted images. Thus, DWI seems to be the most sensitive sequence for detecting changes in patients with suspected CJD. Moreover, its short scanning time ensures that fewer artifacts occur, especially in the case of myoclonus.

Aged↗
PubMed1986

The diffusion of MRI: patterns of siting and ownership in an era of changing incentives.

The rate and pattern of magnetic resonance imaging (MRI) siting and ownership are examined in the context of the current turbulent health-care environment. By the end of 1984, 151 MRI units were located at 134 different sites. There was one MRI unit for every 1.55 million Americans. Most of the largest metropolitan areas had at least one unit. Overall, however, the diffusion rate of MRI has lagged behind that of computed tomography (CT). Trends in magnet preference, siting, and ownership are evolving. While the majority of all units are located within hospitals, the diffusion of nonhospital-based MRI units is accelerating. The deployment of hospital-based units is progressing at a slower rate, largely limited to academic institutions and urban centers. Purchase of superconducting and permanent magnets is accelerating, while that of resistive units is decreasing. Likewise, there is a trend toward adoption of intermediate (0.5 T-0.6 T) and large (1.0 T or 1.5 T) magnets. Ownership arrangements are highly varied and characterized by increased efforts at risk-sharing, trends that reflect a more competitive, profit-oriented medical-care environment. An analysis of recent health-policy initiatives and evolving market factors helps to explain some of these observations. Increased cost-consciousness, prospective reimbursement systems, loopholes in current regulations, and increased competition among health-care providers are influencing the diffusion of MRI and may herald the fate of other expensive medical technologies in the near future.

Delivery of Health Care↗
PubMed2004

The use of 19F spectroscopy and diffusion-weighted MRI to evaluate differences in gene-dependent enzyme prodrug therapies.

To evaluate noninvasive measures of gene expression and tumor response in a gene-dependent enzyme prodrug therapy (GDEPT), a bifunctional fusion gene between Saccharomyces cerevisiae cytosine deaminase (CD) and Haemophilus influenzae uracil phosphoribosyltransferase (UPRT) was constructed. CD deaminates 5-fluorocytosine (5FC) to 5-fluorouracil (5FU), and UPRT subsequently converts 5FU to fluorouridine monophosphate, and both of these reactions can be monitored noninvasively in vitro and in vivo using 19F magnetic resonance spectroscopy (MRS). Following transient transfection the CD-UPRT fusion protein exhibited both UPRT and CD enzymatic activities as documented by 19F MRS. In addition, an increase in CD activity and thermal stability was witnessed for the fusion protein compared to native CD. Stable expression of CD-UPRT in 9L glioma cells increased both 5FC and 5FU sensitivity in vitro compared to CD-expressing and wild-type 9L cells. Noninvasive 19F MRS of both CD and UPRT gene function in vivo demonstrated that in animals bearing CD-expressing tumors there was limited conversion of 5FC to 5FU with no measurable accumulation of cytotoxic fluorinated nucleotides (F-nucs). In contrast, CD-UPRT-expressing tumors had increased CD gene activity with a threefold higher intratumoral accumulation of 5FU and significant generation of F-nucs. Finally, CD-UPRT yielded increased efficacy in an orthotopic animal model of high-grade glioma. More importantly, early changes in cellular water mobility, which are felt to reflect cellular death, as measured by diffusion-weighted MRI, were predictive of both durable response and increased animal survival. These results demonstrate the increased efficacy of the CD-UPRT GDEPT compared to CD alone both biochemically and in a preclinical model and validate both 19F MRS and diffusion-weighted MRI as tools to assess gene function and therapeutic efficacy.

Animals↗