ERA Collection:

Reliability of two techniques for assessing cerebral iron deposits from structural MRI

Sat, 01 Jan 2011 00:00:00 GMT

Title: Reliability of two techniques for assessing cerebral iron deposits from structural MRI Authors: Valdés Hernández, Maria C.; Jeong, Tina H.; Murray, Catherine; Bastin, Mark E.; Chappell, Francesca M.; Deary, Ian J.; Wardlw, Joanna M. Abstract: Purpose: To test the reliability of two computational methods for segmenting cerebral iron deposits (IDs) in the ageing brain, given that its measurement in MRI is challenging due to the similar effect produced by other minerals, especially calcium, on T2*-weighted sequences. Materials and Methods: T1-, T2*-weighted and FLAIR MR brain images obtained at 1.5T from 70 subjects in their early 70s who displayed a wide range of brain IDs were analyzed. The first segmentation method used a multispectral approach based on the fusion of two or more structural sequences registered and mapped in the red/green color space followed by Minimum Variance Quantization. The second method employed a combined thresholding, size and shape analysis using T2*-weighted images augmented with visual information from T1-weighted data. Results: Both segmentation techniques had high intra- and inter-observer agreement (95 % CI = ± 57 voxels in a range from 0 to 1800), which decreased in subjects with significant microbleeds and/or IDs. However, the thresholding method was more observer dependent in identifying microbleeds and IDs boundaries than the multispectral approach. Conclusion: Both techniques proved to be in agreement and have good intra- and inter-observer reliability. However, they have limitations, specifically with regard to automation and observer independence, so further work is required to develop fully user-independent methods of identifying cerebral IDs.

Retinal arteriolar geometry is associated with cerebral white matter hyperintensities on MRI

Wed, 01 Dec 2010 00:00:00 GMT

Title: Retinal arteriolar geometry is associated with cerebral white matter hyperintensities on MRI Authors: Doubal, F.N.; de Haan, R; MacGillivray, T.J.; Cohn-Hokke, P.; Dhillon, B.; Dennis, M.S.; Wardlaw, J.M. Abstract: Background. Cerebral small vessel disease (lacunar stroke and cerebral white matter hyperintensities) is caused by vessel abnormalities of unknown aetiology. Retinal vessels show developmental and pathophysiological similarities to cerebral small vessels and microvessel geometry may influence vascular efficiency. Hypothesis. We hypothesized that retinal arteriolar branching angles or co-efficients (the ratio of the sum of the cross sectional areas of the two daughter vessels to the cross sectional area of the parent vessel at an arteriolar bifurcation) may be associated with cerebral small vessel disease. Methods. We performed a cross-sectional observational study in a tertiary referral hospital, United Kingdom. An experienced stroke physician recruited consecutive patients presenting with lacunar ischaemic stroke with a control group consisting of patients with minor cortical ischaemic stroke. We performed brain magnetic resonance imaging to assess the recent infarct and periventricular and deep white matter hyperintensities. We subtyped stroke with clinical and radiological findings. We took digital retinal photography to assess retinal arteriolar branching co-efficients and branching angles using a semi-automated technique. Results. We recruited 205 patients (104 lacunar stroke, 101 cortical stroke), mean age 68 (Standard Deviation 12) years. With multivariate analysis, increased branching coefficient was associated with periventricular white matter hyperintensities (p=0.006) and ischaemic heart disease (p<0.001); decreased branching co-efficient with deep white matter hyperintensities (p=0.003) but not with lacunar stroke subtype (p=0.96). We found no associations with retinal branching angles. Conclusions. Retinal arteriolar geometry differs between cerebral small vessel phenotypes. More research is needed to ascertain the clinical significance of these findings.

A systematic review of dynamic cerebral and peripheral endothelial function in lacunar stroke versus controls

Tue, 01 Jun 2010 00:00:00 GMT

Title: A systematic review of dynamic cerebral and peripheral endothelial function in lacunar stroke versus controls Authors: Stevenson, Susan F.; Doubal, Fergus N.; Shuler, Kirsten; Wardlaw, Joanna M. Abstract: Background: The aetiology of cerebral small vessel disease is unknown. An association with endothelial dysfunction has been suggested. We systematically assessed all relevant studies of dynamic endothelial function in patients with lacunar stroke, as a marker of small vessel disease. Methods: We searched for studies of cerebral or peripheral vascular reactivity in patients with lacunar or cortical (i.e. large artery atheromatous) ischaemic stroke or non-stroke controls. We calculated standardised mean difference (SMD) in vascular reactivity, +/- 95% confidence intervals (CI) between small vessel disease and control groups. Results: Sixteen publications (974 patients) were included. In lacunar stroke: cerebrovascular reactivity (n=534) was reduced compared with age-matched normal (SMD -0.94, 95%CI -1.17, -0.70), but not age+risk factor-matched controls (SMD 0.08, 95%CI -0.36, 0.53) or cortical strokes (SMD -0.29, 95%CI -0.69, 0.11); forearm flow mediated dilatation (n=401) was reduced compared with age-matched normal controls (SMD -1.04, 95%CI -1.33, -0.75) and age+risk factor-matched controls (SMD -0.94, 95%CI -1.26, -0.61), but not cortical strokes (SMD -0.23, 95%CI -0.55, 0.08). Conclusions: Endothelial dysfunction is present in patients with lacunar stroke but may simply reflect exposure to vascular risk factors and having a stroke, as a similar degree of dysfunction is found in cortical (large artery atheromatous) stroke. Current data do not confirm that endothelial dysfunction is specific to small vessel stroke. Future studies should include controls with non-lacunar stroke.

Brain choline concentration: early quantitative marker of ischemia and infarct expansion?

Wed, 01 Sep 2010 00:00:00 GMT

Title: Brain choline concentration: early quantitative marker of ischemia and infarct expansion? Authors: Karaszewski, B.; Thomas, R.G.R.; Chappell, F.M.; Armitage, P.A.; Carpenter, T.K.; Lymer, G.K.S.; Dennis, M.S.; Marshall, I.; Wardlaw, J.M. Abstract: Objective: Better prediction of tissue prognosis in acute stroke might improve treatment decisions. We hypothesized that there are metabolic ischemic disturbances measurable non-invasively by proton MR spectroscopy (1HMRS) that occur earlier than any structural changes visible on diffusion tensor imaging (DTI), which may therefore serve for territorial identification of “tissue at risk”. Methods: We performed multi-voxel 1HMRS plus DTI within a maximum of 26 hours, and DTI at three-seven days, after ischemic stroke. We compared choline, lactate, NAA, creatine concentrations in normal-appearing voxels that became infarcted("infarct expansion”), with normal-appearing voxels around the infarct that remained “healthy”(“non-expansion”) on follow-up DTI. Each “infarct expansion” voxel was additionally classified as either “complete infarct expansion”(infarcted tissue on follow-up DTI covered ≥50% of the voxel) or “partial infarct expansion”(<50% of voxel). Results: In 31 patients (NIHSS:0–28) there were 108 infarct "non-expansion” voxels and 113 infarct "expansion” voxels (of which 80 were “complete expansion” and 33 “partial expansion” voxels). Brain choline concentration increased for each change in expansion category from "non-expansion", via "partial expansion" to "complete expansion" (2423, 3843, 4158i.u.; p<0.05). Changes in lactate, NAA and creatine concentrations in expansion category were insignificant although for lactate there was a tendency to such association. Conclusions: Choline concentration measurable with 1HMRS was elevated in peri-ischemic normal-appearing brain that became infarcted by three-seven days. The degree of elevation was associated with the amount of infarct expansion. 1HMRS might identify DTI-normal appearing tissue at risk of conversion to infarction in early stroke.