Comparison of optimized and standard diffusion-weighted imaging at 1.5T for the detection of acute lesions in patients with transient ischemic attack

Computed diffusion-weighted imaging in patients with transient neurovascular symptoms with and without ischemic infarction

PURPOSE

Detection of ischemic lesions in patients with transient neurovascular symptoms is relevant for the estimation of the risk of a subsequent stroke and etiological classification. To improve detection rates, different technical approaches have been used, such as diffusion-weighted imaging (DWI) with high b-values or higher magnetic field strength. Here, we sought to investigate the value of computed DWI (cDWI) with high b-values in these patients.

METHODS

From an MRI report database we identified patients with transient neurovascular symptoms who underwent repeated MRI including DWI. cDWI was calculated with a monoexponential model with high b-values (2000, 3000, and 4000 s/mm2) and compared to the routinely used standard DWI with regard to presence of ischemic lesions and lesion detectability.

RESULT

Overall 33 patients with transient neurovascular symptoms (71 [IQR 57-83.5] years; 21 [63.6%] male) were included. On DWI, acute ischemic lesions were observed in 22 (78.6%). Acute ischemic lesions were observed in 17 (51.5%) patients on initial DWI, and in 26 (78.8%) patients on follow-up DWI. Lesion detectability was rated significantly better on cDWI at 2000s/mm2 compared to standard DWI. In 2 (9.1%) patients, cDWI at 2000s/mm2 revealed an acute ischemic lesion proven on follow-up standard DWI which was not detected with certainty on the initial standard DWI.

CONCLUSION

cDWI might be a valuable addition to routinely acquired standard DWI in patients with transient neurovascular symptoms since its use might result in improved ischemic lesion detection. A b-value of 2000s/mm2 seems most promising for clinical practice.

An assessment of the cost-effectiveness of magnetic resonance, including diffusion-weighted imaging, in patients with transient ischaemic attack and minor stroke: a systematic review, meta-analysis and economic evaluation

BACKGROUND

Patients with transient ischaemic attack (TIA) or minor stroke need rapid treatment of risk factors to prevent recurrent stroke. ABCD2 score or magnetic resonance diffusion-weighted brain imaging (MR DWI) may help assessment and treatment.

OBJECTIVES

Is MR with DWI cost-effective in stroke prevention compared with computed tomography (CT) brain scanning in all patients, in specific subgroups or as 'one-stop' brain-carotid imaging? What is the current UK availability of services for stroke prevention?

DATA SOURCES

Published literature; stroke registries, audit and randomised clinical trials; national databases; survey of UK clinical and imaging services for stroke; expert opinion.

REVIEW METHODS

Systematic reviews and meta-analyses of published/unpublished data. Decision-analytic model of stroke prevention including on a 20-year time horizon including nine representative imaging scenarios.

RESULTS

The pooled recurrent stroke rate after TIA (53 studies, 30,558 patients) is 5.2% [95% confidence interval (CI) 3.9% to 5.9%] by 7 days, and 6.7% (5.2% to 8.7%) at 90 days. ABCD2 score does not identify patients with key stroke causes or identify mimics: 66% of specialist-diagnosed true TIAs and 35-41% of mimics had an ABCD2 score of ≥ 4; 20% of true TIAs with ABCD2 score of < 4 had key risk factors. MR DWI (45 studies, 9078 patients) showed an acute ischaemic lesion in 34.3% (95% CI 30.5% to 38.4%) of TIA, 69% of minor stroke patients, i.e. two-thirds of TIA patients are DWI negative. TIA mimics (16 studies, 14,542 patients) make up 40-45% of patients attending clinics. UK survey (45% response) showed most secondary prevention started prior to clinic, 85% of primary brain imaging was same-day CT; 51-54% of patients had MR, mostly additional to CT, on average 1 week later; 55% omitted blood-sensitive MR sequences. Compared with 'CT scan all patients' MR was more expensive and no more cost-effective, except for patients presenting at > 1 week after symptoms to diagnose haemorrhage; strategies that triaged patients with low ABCD2 scores for slow investigation or treated DWI-negative patients as non-TIA/minor stroke prevented fewer strokes and increased costs. 'One-stop' CT/MR angiographic-plus-brain imaging was not cost-effective.

LIMITATIONS

Data on sensitivity/specificity of MR in TIA/minor stroke, stroke costs, prognosis of TIA mimics and accuracy of ABCD2 score by non-specialists are sparse or absent; all analysis had substantial heterogeneity.

CONCLUSIONS

Magnetic resonance with DWI is not cost-effective for secondary stroke prevention. MR was most helpful in patients presenting at > 1 week after symptoms if blood-sensitive sequences were used. ABCD2 score is unlikely to facilitate patient triage by non-stroke specialists. Rapid specialist assessment, CT brain scanning and identification of serious underlying stroke causes is the most cost-effective stroke prevention strategy.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Improving detection of ischemic lesions at 3 Tesla with optimized diffusion-weighted magnetic resonance imaging

BACKGROUND AND PURPOSE

This study compared three different combinations of DWI parameters: three and six diffusion imaging directions (3dir and 6dir, respectively) using b=1000 or 2000 s/mm(2) (b1000 or b2000, respectively) to improve detection of recent ischemic lesions at 3 Tesla (3 T).

MATERIALS AND METHODS

A total of 47 consecutive patients underwent three DWI scans: 3dir b1000; 6dir b1000; and 6dir b2000. Qualitative visual analysis was performed by three readers based on evaluation of the number of lesions, presence of artifacts and diagnostic confidence. Interobserver agreement, sensitivity, specificity, and positive and negative predictive values were calculated.

RESULTS

Forty-five lesions were detected by 3dir b1000, 52 by 6dir b1000 and 56 by 6dir b2000 in 30 patients. The additional lesions identified by 6dir b2000 were either small or located in the posterior fossa. Sensitivity with 6dir b2000 was significantly higher than with 3dir b1000 (98.1% vs 77.4%; P<0.05).

CONCLUSION

At 3 T, 6dir b2000 DWI detected more acute ischemic lesions than 3dir b1000, particularly small lesions and those located in the brain stem.

Tips and traps in brain MRI: applications to vascular disorders

The French Society of Radiology's guide to good use of medical imaging examinations recommends MRI as the first-line examination for exploring cerebrovascular events or disorders. This paper will discuss the main traps in the images when stroke is suspected and provide the technical tips or knowledge necessary for an optimal radiological report.

[Filter content after carotid angioplasty and stenting: relation to ischemic lesions in diffusion-weighted imaging]

OBJECTIVES

To evaluate the relation between the material retrieved from distal filters after carotid angioplasty and stenting and the development of ischemic brain lesions in diffusion-weighted imaging (DWI). To determine the influence of demographic, clinical, and procedural variables in the pathogenesis of emboli and in ischemia after carotid angioplasty and stenting.

MATERIAL AND METHODS

We submitted the contents of the filters of 76 patients (60 men; mean age, 68.39 years; range, 46-82) who had undergone angioplasty and stenting for severe stenosis of the internal carotid artery for histologic analysis evaluating volume (< 1 λ = 0.001 ml = 1 μl; 1-10 λ; and > 10 λ) and the composition of the particles. All patients underwent DWI before and 24 hours after the procedure; we recorded whether lesions appeared and their number, size, and distribution. We correlated the findings with demographic, clinical, and procedural variables.

RESULTS

Symptoms were present before the procedure in 58 (76.3%) patients. Particles were present in 49 (64.5%) of the filters; most particles (77.5%) were 1 λ with a predominance of fibrin-platelet aggregates, cell remnants, and cholesterol crystals. DWI after the procedure detected lesions in 12 (15.8%) patients. We found no statistically significant correlation between filter contents and lesion detection after the procedure or between filter contents and other variables.

CONCLUSIONS

Ischemia after carotid angioplasty and stenting does not depend solely on the embolic load and its nature. We consider that the lower prevalence of postprocedural lesions in our series compared to others suggests that appropriate patient selection and experience minimize the negative influence of some variables like age in their development.

CT and MR in non-neonatal hypoxic-ischemic encephalopathy: radiological findings with pathophysiological correlations

Non-neonatal hypoxic-ischemic encephalopathy is a clinical condition often related to cardiopulmonary arrest that demands critical management and treatment decisions. Management depends mainly on the degree of neurological impairment and prognostic considerations. Computed tomography (CT) is often used to exclude associated or mimicking pathology. If any, only nonspecific signs such as cerebral edema, sulci effacement, and decreased gray matter (GM)/white matter (WM) differentiation are evident. Pseudosubarachnoid hemorrhage, a GM/WM attenuation ratio <1.18, and inverted GM attenuation are associated with a poor prognosis. Magnetic resonance (MR) imaging is more sensitive than CT in assessing brain damage in hypoxic-ischemic encephalopathy. Some MR findings have similarities to those seen pathologically, based on spatial distribution and time scale, such as lesions distributed in watershed regions and selective injury to GM structures. In the acute phase, lesions are better depicted using diffusion-weighted imaging (DWI) because of the presence of cytotoxic edema, which, on T2-weighted images, only become apparent later in the early subacute phase. In the late subacute phase, postanoxic leukoencephalopathy and contrast enhancement could be observed. In the chronic phase, atrophic changes predominate over tissue signal changes. MR can be useful for estimating prognosis when other tests are inconclusive. Some findings, such as the extent of lesions on DWI and presence of a lactate peak and depleted N-acetyl aspartate peak on MR spectroscopy, seem to have prognostic value.

The utility of high b-value DWI in evaluation of ischemic stroke at 3T

PURPOSE

The utility of DWI with high b-value in ischemic stroke is still unsettled. The purpose of this study is to compare high b-value (3000) and standard b-value (1000) diffusion-weighted images in patients with ischemic stroke at 3T.

MATERIALS AND METHODS

27 patients with acute stroke who were admitted to the hospital during the first 24h after symptom onset were included in this study. All patients had a brain MRI study with stroke protocol including standard (b=1000) DWI and high b-value (b=3000) DWI sequences at 3T MR scanner. Number and localization of the lesions were assessed MR signal intensities (SI), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contrast ratio (CR) and apparent diffusion coefficient (ADC) values of the lesions and normal parenchyma on DWI with b=1000 and b=3000 sequences were measured.

RESULTS

All patients with acute stroke revealed hyperintense lesions due to restricted diffusion on DWI with both b-values. However, lesions of restricted diffusion were more conspicuous in b=3000 value DWI than b=1000, and additional 4 ischemic lesions were detected on b=3000 DWI. SNR, CNR, SI and also ADC values in both stroke area and normal parenchyma were lower at b=3000 than the value at b=1000. At b=3000, CR was significantly greater than b=1000 images.

CONCLUSIONS

Although quantitative analysis shows higher SI, SNR and CNR values with standard b-value (b=1000) diffusion-weighted imaging, using higher b-value may still be beneficial in detecting additional subtle lesions in patients whose clinical findings are not correlated with standard b-value DWI in stroke.

Higher lesion detection by 3.0T MRI in patient with transient global amnesia

PURPOSE

Transient global amnesia (TGA) patients were retrospectively reviewed to determine the usefulness of high-field strength MRI in detecting probable ischemic lesions in TGA.

MATERIALS AND METHODS

We investigated the lesion detection rate in patients with TGA using 1.5T and 3.0T MRI. Acute probable ischemic lesions were defined as regions of high-signal intensity in diffusion weighted image with corresponding low-signal intensity in apparent diffusion coefficient map.

RESULTS

3.0T MRI showed 11 out of 32 patients with probable ischemic lesions in the hippocampus with mean lesion size of 2.8 +/- 0.6 mm, whereas 1.5T MRI detected no lesion in any of 11 patients. There were no significant differences in clinical characteristics between the groups of 1.5 and 3.0T MRI.

CONCLUSION

High-field strength MRI has a higher detection rate of probable ischemic lesions than low-field strength MRI in patients with TGA.