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PubMedDate not supplied

Diffusion-weighted MRI features of brain abscess and cystic or necrotic brain tumors: comparison with conventional MRI.

BACKGROUND AND PURPOSE: The purpose of this study was to determine whether diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) can be used to distinguish brain abscesses from cystic or necrotic brain tumors, which are difficult to distinguish by conventional magnetic resonance imaging (MRI) techniques. METHODS: Eleven consecutive patients with brain abscesses [10 pyogenic and 1 toxoplasmosis (in an AIDS patient)] and 15 with cystic or necrotic brain gliomas or metastases were enrolled in this study. None of these lesions had apparent hemorrhage based on T1-weighted image (T1WI). The DWI was performed using a 1.5-T system, single-shot spin-echo echo-planar pulse sequence with b=1000 s/mm(2). The ADC was calculated using a two-point linear regression method at b=0 and b=1000 s/mm(2). The ratio (ADCR) of the lesion ADC to control region ADC was also measured. RESULTS: Increased signal was seen in all of the pyogenic abscess cavities to variable degrees on DWI. In vivo ADC maps showed restricted diffusion in the abscess cavity in all pyogenic abscesses [0.65+/-0.16 x 10(-3) (mean+/-S.D.) mm(2)/s, mean ADCR=0.63]. The case with multiple toxoplasmosis abscesses showed low signal intensity on DWI and high ADC values (mean 1.9 x 10(-3) mm(2)/s, ADCR=2.24). All cystic or necrotic tumors but one showed low signal intensity on DWI and their cystic or necrotic areas had high ADC values (2.70+/-0.31 x 10(-3) mm(2)/s, mean ADCR=3.42). One fibrillary low-grade astrocytoma had a high DWI signal intensity and a low ADC value in its central cystic area (0.44 x 10(-3) mm(2)/s, ADCR=0.49). Postcontrast T1WIs yielded a sensitivity of 60%, a specificity of 27.27%, a positive predictive value (PPV) of 52.94%, and a negative predictive value (NPV) of 33.33% in the diagnosis of necrotic tumors. DWI yielded a sensitivity of 93.33%, a specificity of 90.91%, a PPV of 93.33%, and a NPV of 90.91%. The area under receiver operating characteristic (ROC) curves for postcontrast T1WI was 0.44 and DWI was 0.92. Analysis of these areas under the ROC curves indicates significant difference between postcontrast T1WI and DWI (P<.001). CONCLUSION: With some exceptions, DWI is useful in providing a greater degree of confidence in distinguishing brain abscesses from cystic or necrotic brain tumors than conventional MRI and seems to be a valuable diagnostic tool.

Brain↗
PubMed2003

Diffusion tensor MRI of myocardial fibers and sheets: correspondence with visible cut-face texture.

PURPOSE: To test the hypothesis that the primary, secondary, and tertiary eigenvectors of the diffusion tensor (DT) measured with DT-MRI correspond to the fiber, sheet, and sheet normal directions, respectively, we compared DT-MRI data with the texture visible in the cut face of fresh bovine myocardium. MATERIALS AND METHODS: DT-MRI and optical images obtained under identical conditions were compared objectively. Ink prints were made of the cut tissue, and the local orientations within these images were defined by analysis of local autocorrelations for regions matching DT-MRI pixels. Deviation angles between the cleavage orientations and the diffusion eigenvectors were analyzed in eight specimens sliced in three orthogonal planes. RESULTS: Root-mean-square (RMS) angular disparity was 11 degrees between the first eigenvectors of the DT and the fiber direction, 14 degrees between the second eigenvector and the sheet direction, 14 degrees between the third eigenvector and the sheet normal direction, and 15 degrees between the tensor orientation in the imaging plane and the cleavage orientation of the cut face. CONCLUSION: The results support a parallel relationship between the eigenvectors of the DT and symmetry axes of the myocardial architecture. Specifically, the first, second and third eigenvectors correspond to the fiber, sheet, and sheet normal directions, respectively.

Animals↗
PubMed1998

Posterior leukoencephalopathy without severe hypertension: utility of diffusion-weighted MRI.

OBJECTIVE: Standard MRI confirms the diagnosis of posterior leukoencephalopathy syndrome (PLES), recently associated with an increasing number of medical conditions. In PLES, T2-weighted MRI demonstrates hyperintensity spreading out from posterior brain regions; the pathophysiology remains mysterious. In the acute setting, diffusion-weighted imaging (DWI), but not standard MR imaging, can distinguish ischemic injury from those conditions known to cause vasogenic brain edema. DWI is potentially valuable in understanding the pathophysiology of PLES and in diagnosing patients who do not have previously known risk factors. METHODS: Serial CT and MRI studies (including DWI, apparent diffusion coefficient [ADC] maps, and, in one instance, perfusion-weighted imaging) were performed in three female patients with a neurologic syndrome consistent with PLES while hospitalized for treatment of other conditions. RESULTS: None of the patients had previously described risk factors for PLES; all had only mild elevations in blood pressure. MRI showed large, abnormal, T2 hyperintense regions in the posterior cerebrum with corresponding hyperintensity on ADC maps-signal characteristics predominantly consistent with vasogenic edema. There were also smaller patchy posterior cortical regions with decreased ADC and bright DWI consistent with infarction in one, and dramatic conversion of a large region to an ischemic pattern in another. CONCLUSIONS: ADC maps and DWI can successfully differentiate PLES from early cerebral ischemia, thus playing a pivotal role in treatment decisions. PLES is associated with a wider variety of conditions than has been previously reported and is not always reversible. Hyperintense DWI signal in patients with the syndrome likely marks a tissue stage of permanent brain injury.

Adult↗
PubMedDate not supplied

Diffusion-weighted MRI in acute mutism.

Mutism defined as a complete loss of speech may be related to psychiatric or neurologic disorders. The ischemic stroke origins of mutism are often difficult to assess at the acute stage. Accordingly, the search for the underlying mechanism as the localization of the damages may be difficult by conventional radiological techniques. Diffusion-weighted (DWI) MRI may accurately identify patients with acute ischemic stroke and distinguish them from those who mimic acute stroke better than clinical and conventional neuroradiological methods. This report aims to demonstrate the utility of DWI-MRI in the diagnosis of acute mutism.

Acute Disease↗
PubMed1998

Prediction of stroke outcome with echoplanar perfusion- and diffusion-weighted MRI.

OBJECTIVES: We examined the utility of echoplanar magnetic resonance perfusion imaging and diffusion-weighted imaging (DWI) in predicting stroke evolution and outcome in 18 patients with acute hemispheric infarction. METHODS: Patients were studied within 24 hours (mean, 12.2 hours), subacutely (mean, 4.7 days), and at outcome (mean, 84 days). Comparisons were made between infarction volumes as measured on perfusion imaging (PI) and isotropic DWI maps, clinical assessment scales (Canadian Neurological Scale, Barthel Index, and Rankin Scale), and final infarct volume (T2-weighted MRI). RESULTS: Acute PI lesion volumes correlated with acute neurologic state, clinical outcome, and final infarct volume. Acute DWI lesions correlated less robustly with acute neurologic state, but correlated well with clinical outcome and final infarct volume. Three of six possible patterns of abnormalities were seen: PI lesion larger than DWI lesion (65%), PI lesion smaller than DWI lesion (12%), and DWI lesion but no PI lesion (23%). A pattern of a PI lesion larger than the DWI lesion predicted DWI expansion into surrounding hypoperfused tissue (p < 0.05). In the other two patterns, DWI lesions did not enlarge, suggesting that no significant increase in ischemic lesion size occurs in the absence of a larger perfusion deficit. CONCLUSIONS: Combined early PI and DWI can define different acute infarct patterns, which may allow the selection of rational therapeutic strategies based on the presence or absence of potentially salvageable ischemic tissue.

Adult↗
PubMed2003

Changes on diffusion-weighted MRI with focal motor status epilepticus: case report.

Transient imaging abnormalities, including changes on diffusion-weighted imaging (DWI), may be seen in focal status epilepticus. The changes on DWI provide am insight into the pathophysiology. We report a 53-year-old man with focal motor status epilepticus involving the left hand, arm and face with focal slowing on EEG. The apparent diffusion coefficients (ADC) were higher in the affected hemisphere than on the other side. At 10 days and 6 weeks after the end of the seizures, we saw normal ADCs and atrophy of the affected hemisphere. We conclude that the MRI findings indicate both cytotoxic and vasogenic oedema during seizure activity and subsequent loss of brain parenchyma.

Arm↗
PubMed2002

Combined X-ray angiography and diffusion-perfusion MRI for studying stroke evolution after rt-PA treatment in rats.

Clinical studies on rt-PA (recombinant tissue-type plasminogen activator) treatment of stroke showed a favorable outcome. However, there are reports of harmful effects of t-PA via the potentiation of excitotoxic injury. We used combined X-ray angiography and MRI imaging to study the balance between the beneficial effect of reperfusion and secondary detrimental effects of rt-PA. Therefore, rats (n=15) were assigned to three groups according to recanalization or lack thereof of the middle cerebral artery (MCA) and rt-PA or saline treatment in an embolic stroke model. Diffusion and perfusion MRI showed that animals had significantly improved perfusion values and final infarct size when recanalization was successful. However, final infarct volumes at 6 h post stroke onset were greater in the rt-PA group compared to controls at comparable perfusion values when the MCA did not recanalize after treatment (67.4+/-5.4 versus 47.7+/-17.9% of ipsilateral hemisphere, P=0.042). Our results demonstrate that the combination of angiography and MR-imaging is useful to further evaluate rt-PA treatment of thromboembolic stroke.

Animals↗
PubMed2002

In vivo diffusion-weighted MRI of the breast: potential for lesion characterization.

PURPOSE: To investigate the potential of apparent diffusion coefficients (ADCs) in characterizing breast lesions in vivo. MATERIALS AND METHODS: Two diffusion-weighted (DW) sequences were implemented on a 1.5 Tesla scanner, with low b-value orthogonal and high b-value tetrahedral sensitized sequences. The orthogonal sequence was evaluated on 16 normal volunteers and 23 patients with known lesion types (six benign and 17 malignant). The tetrahedral sequence was evaluated on a smaller number of subjects: two normal, two malignant, and two benign. RESULTS: The mean value of the ADC of the malignant tumors was reduced compared to that of the benign lesions and normal tissue. This finding was related to the increased cellularity of the malignant lesions. The ADC values were elevated for all tissue types with the low b-value sequence as compared to the high b-value sequence, indicating contributions from perfusion effects at the low b-values. CONCLUSION: The study clearly shows that DW-MRI can help characterize breast lesions in vivo.

Breast↗
PubMed2001

[Bithalamic infarcts as the etiology of acute stupor. Early diagnosis with diffusion-weighted MRI].

Fast diagnostic evaluation of somnolent or unconscious patients is a demanding task for neurologists. Apart from postictal, metabolic, and toxic causes, vascular syndromes must be rapidly identified in order to initiate a specific fibrinolytic therapy. Given its high mortality if not treated in time, this dictum holds especially true for basilar artery occlusion. However, certain ischemic lesions in the vascular territory of the basilar artery without occlusion of the basilar artery itself can also result in somnolence, sopor, or even unconsciousness. Here we report early imaging signs of bithalamic infarctions as the cause of acute sopor using diffusion-weighted (DW)-MRI, which reliably identifies acute bithalamic infarctions as a possible cause of acute consciousness disturbance, even with noncooperative patients.

Acute Disease↗
PubMed2000

A quantitative analysis of cortical spreading depression events in the feline brain characterized with diffusion-weighted MRI.

Cortical spreading depression (CSD) in the gyrencephalic cat brain was detected with diffusion-weighted echoplanar (DWEP) magnetic resonance imaging (4-8/min for 1-2 hours) using a horizontal imaging plane through the suprasylvian (SG) and marginal gyri. A t-statistic mapping technique allowed a quantitative characterization of the passage of events through single-image pixels (0.15 mm(2)), thus providing a resolution unavailable to previous studies in which time-dependent changes instead were derived from averaging data over relatively large ROIs. Using the enhanced analysis, CSD events initiated by KCl could be quantified for the first time as primary or secondary according to their spatial and temporal features. Primary events covered 26.2 +/- 9.9 mm(2)of cortical surface (mean +/- SD, n = 7 experiments) and propagated rapidly (3.5 +/- 0.65 mm * min(-1)) with a hemispherical geometry. In contrast, the subsequent secondary events were multiple, spatially restricted (covering 7.6 +/- 4.6 mm(2), P < 0.005), slower in propagation (2.6 +/- 0.41 mm * min(-1), P < 0.012), and often confined to the originating gyrus (26 out of 59 events). However, both event types were associated with significantly reduced apparent diffusion coefficients (ADCs; from 800 to approximately 660 x 10(-6) mm(2)* s(-1), P < 0.05) that were similar for both primary (21 +/- 5.1%) and secondary waves (18 +/- 7. 7%) and that had similar durations (full width at half-maximal height: 86 +/- 17 vs. 79 +/- 20 seconds, respectively). These findings associate CSD for the first time with two categories of ADC disturbance that are similar in amplitude and duration but that differ in spatial extent, velocity, and extensiveness of spread.

Animals↗
PubMed2002

Characterization of anisotropy in high angular resolution diffusion-weighted MRI.

The methods of group theory are applied to the problem of characterizing the diffusion measured in high angular resolution MR experiments. This leads to a natural representation of the local diffusion in terms of spherical harmonics. In this representation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotropic diffusion from multiple fiber directions fall into distinct and separable channels. This decomposition can be determined for any voxel without any prior information by a spherical harmonic transform, and for special cases the magnitude and orientation of the local diffusion may be determined. Moreover, non-diffusion-related asymmetries produced by experimental artifacts fall into channels distinct from the fiber channels, thereby allowing their separation and a subsequent reduction in noise from the reconstructed fibers. In the case of a single fiber, the method reduces identically to the standard diffusion tensor method. The method is applied to normal volunteer brain data collected with a stimulated echo spiral high angular resolution diffusion-weighted (HARD) acquisition.

Anisotropy↗
PubMed2003

Diffusion-weighted MRI of haemangioblastomas and other cerebellar tumours.

We examined the signal intensity on diffusion-weighted imaging and the apparent diffusion coefficients (ADC) relative to normal cerebellum of the solid portions of 10 cerebellar haemangioblastomas and 12 other cerebellar tumours: three metastases, three medulloblastomas, three malignant lymphomas, an atypical teratoid rhabdoid tumour, an ependymoma and a subependymoma. The tumours were confirmed histopathologically except for one metastasis with pathological diagnosis of the primary lesion. In nine of the haemangioblatomas, the solid and contrast-enhancing portions gave low signal on DWI, but this was not seen in the other tumours. The ADC was increased in haemangioblastomas. These findings may indicate rich vascular spaces of the haemangioblastomas. DWI may be useful for distinguishing haemangioblastomas from other enhancing cerebellar tumours.

Adult↗
PubMed1997

Prediction of delayed ischemic injury with diffusion-weighted MRI following temporary middle cerebral artery occlusion in rats.

Early reductions in the apparent diffusion coefficient of water (ADC) during focal cerebral ischemia are often reversible with reperfusion. With sustained ischemia, the magnitude of the ADC reduction generally increases with time, which could reflect increased severity of ischemic damage. Thus, a threshold in ADC reduction may exist beyond which damage can not be reversed with reperfusion. The goal of this study was to determine if such a threshold exists that is independent of the duration of ischemia in a rat model. Rats were subjected to either 30, 60, or 90 min of temporary middle cerebral artery occlusion. ADC maps acquired just before and 30 min after reperfusion were compared to histology performed after a 72 h survival period to determine the relationship between ADC reduction and final ischemic injury. Significant variability in tissue recovery was observed for the 30 min group. Regions with ADC reductions of up to 45% often recovered, while some regions not exhibiting any change in ADC during occlusion showed ischemic injury at 72 h. Similar observations were made in cortical regions of the 60 min group. In the caudate-putamen, reduced ADC was often associated with ischemic injury. For the 90 min group, results for the caudate-putamen were similar to those for the 60 min group, while reduced ADC was a much better predictor of final ischemic injury in cortical regions than it was in both the 30 and 60 min groups. Thus, no single threshold of ADC reduction that was independent of the duration of ischemia was associated with irreversible injury.

Animals↗
PubMed2002

Diffusion tensor MRI in temporal lobe epilepsy.

The purpose of this study was to investigate the diffusion characteristics of white matter in patients with focal temporal lobe epilepsy (TLE). Diffusion tensor imaging (DTI) was applied to patients and normal controls. Rotationally invariant mean diffusivity and diffusion anisotropy maps were calculated for all subjects. Comparisons between the two groups were performed for several white matter structures. Mean diffusivity and diffusion anisotropy of each selected structure were tested for correlations with age at onset and duration of epilepsy. Significantly lower diffusion anisotropy, and higher diffusivity in directions perpendicular to the axons, was detected in several white matter structures of the patients when compared to the controls. These structures were not located in the temporal lobes. No significant difference in mean diffusivity was detected between the selected structures from the two groups. Diffusion anisotropy was significantly correlated with age at onset of epilepsy in the posterior corpus callosum. Duration of epilepsy was not significantly correlated with the diffusion indices from any of the selected structures. The results of this study suggest that diffusion anisotropy may reveal abnormalities in patients with focal TLE. In addition, these abnormal changes are not necessarily restricted to the temporal lobes but might extend in other brain regions as well. Furthermore, the age at onset of epilepsy may be an important factor in determining the extent of the effect of epilepsy on white matter.

Adult↗
PubMedDate not supplied

Evaluating tumors and tumorlike lesions of the nasal cavity, the paranasal sinuses, and the adjacent skull base with diffusion-weighted MRI.

PURPOSE: The purpose of this study was to analyze the relationship of apparent diffusion coefficients (ADCs) to the malignant degree and the histopathological features of the lesions in the nasal cavity, the paranasal sinuses, and the adjacent skull base. METHOD: We evaluated the differences of the ADCs between the malignancies (n=18) and the benign lesions (n=6). The correlations between lesion ADCs and lesion cellularity, stroma, and necrosis were calculated. RESULTS: The ADCs of the malignancies were significantly lower than the benign lesions (P<0.0125). The ADCs were inversely correlated with tumor cellularity (P<0.01, r=-0.556). CONCLUSIONS: ADCs provide quantitative information that has limited utility in the differential diagnosis between malignant and benign lesions. The correlation of the histopathology of a lesion with ADCs is quite complex and affected by numerous tumor components besides cellularity including keratin, collagen, myxoid stroma, and necrosis.

Adolescent↗
PubMed2003

Remodeling of cardiac fiber structure after infarction in rats quantified with diffusion tensor MRI.

Structural remodeling of myocardium after infarction plays a critical role in functional adaptation. Diffusion tensor magnetic resonance imaging (DTMRI) provides a means for rapid and nondestructive characterization of the three-dimensional fiber architecture of cardiac tissues. In this study, microscopic structural changes caused by MI were evaluated in Fischer 344 rats 4 wk after infarct surgery. DTMRI studies were performed on 15 excised, formalin-fixed rat hearts of both infarct (left anterior descending coronary artery occlusion, n = 8) and control (sham, n = 7) rats. Infarct myocardium exhibited increased water diffusivity (41% increase in trace values) and decreased diffusion anisotropy (37% decrease in relative anisotropy index). The reduced diffusion anisotropy correlated negatively with microscopic fiber disarray determined by histological analysis (R = 0.81). Transmural courses of fiber orientation angles in infarct zones were similar to those of normal myocardium. However, regional angular deviation of the diffusion tensor increased significantly in the infarct myocardium and correlated strongly with microscopic fiber disarray (R = 0.86). These results suggest that DTMRI may provide a valuable tool for defining structural remodeling in diseased myocardium at the cellular and tissue level.

Animals↗
PubMed1999

[Echo-planar diffusion-weighted MRI in the diagnosis of acute ischemic stroke: characterisation of tissue abnormalities and limitations in the interpretation of imaging findings].

INTRODUCTION: An accurate diagnosis is frequently difficult in early stroke. Diffusion-weighted (DW) magnetic resonance imaging (MRI) allows visualization of ischemic parenchyma and quantitative assessment of tissue changes before unequivocal abnormalities appear on T(2)-weighted MRI. METHODS: We analyzed 105 MRI examinations of patients with acute stroke (<24 h) with regard to patterns of abnormalities in T(2)-weighted and DW MRI. Furthermore we assessed the influence of artifacts related to DW echo-planar single-shot MRI on image interpretation. RESULTS: Depending on the time of patient assessment there were three partly overlapping T(2)/DW patterns: (1) in the very early phase (</=1.5 h after symptom onset) there was no T(2) abnormality and no definite abnormality of diffusion; (2) no T(2) abnormality and restricted diffusion (1.5-4 h); (3) T(2) hyperintensity and restricted diffusion (>/=3 h). Typical artifacts (susceptibility distortions, N/2 artifact, chemical shift artifact and eddy currents artifact) had to be considered when interpreting images. CONCLUSIONS: Provided typical artifacts are taken into consideration, echo-planar DW MRI allows a more precise diagnostic assessment in acute stroke.

Acute Disease↗
PubMed2002

On the application of a non-CPMG single-shot fast spin-echo sequence to diffusion tensor MRI of the human brain.

The strong sensitivity of Carr-Purcell-Meiboom-Gill (CPMG) fast spin-echo (FSE) sequences, such as rapid acquisition with relaxation enhancement (RARE), to the phase of the prepared transverse magnetization means that artifact-free single-shot diffusion-weighted images can currently only be obtained with a 30-50% reduction in the signal-to-noise ratio (SNR). However, this phase sensitivity and signal loss can be addressed in FSE sequences that use quadratic phase modulation of the radiofrequency (RF) refocusing pulses to generate a sustained train of stable echoes. Here the first application of such a non-CPMG single-shot FSE (ssFSE) sequence to diffusion tensor MR imaging (DT-MRI) of the human brain is described. This approach provides high SNR diffusion-weighted images that have little or no susceptibility to poor B(0) magnetic field homogeneity and the strong eddy currents typically present in DT-MRI experiments.

Brain↗