Comparison of metabolite levels and water diffusion between cortical and subcortical strokes as monitored by MRI and MRS

Hyperglycaemia in acute lacunar stroke: a Chinese hospital-based study

Admission hyperglycaemia is very common in acute ischaemic stroke (IS) patients and is associated with worse outcome in non-lacunar infarction, but its association with lacunar infarction remains controversial. We investigated the association between hyperglycaemia and clinical outcome in patients with acute lacunar stroke in a hospitalised Chinese population. Consecutive patients with acute IS were enrolled and classified into lacunar and non-lacunar stroke groups based on clinical criteria according to the Oxfordshire Community Stroke Project (OCSP) and findings on brain computed tomography (CT) or magnetic resonance imaging (MRI) scan. Hyperglycaemia was defined as blood glucose > 6.1 mmol/L. Univariate and multivariate analyses were used to examine the association between hyperglycaemia and outcomes in diabetic and non-diabetic groups. The main outcome measure was a poor outcome [defined as modified Rankin Scale (mRS) score ≥ 3] at 12 months after stroke. Of the 2020 acute ISs, 689 (34.1%) were acute lacunar strokes, of which 159 (23%) were diabetic and the other 530 (77%) were non-diabetic. In non-lacunar stroke, admission hyperglycaemia was independently associated with increased risk of poor outcome at 1 year (odds ratio (OR) = 1.782; 95% confidence interval (CI) = 1.340-2.370, p = 0.0005). In lacunar stroke, hyperglycaemia was not associated with functional outcome (OR = 1.337; 95% CI = 0.939-1.093, p = 0.086) irrespective of the diabetic status.

Glutamate level detection by magnetic resonance spectroscopy in patients with post-stroke depression

In recent studies, the glutamate (Glu) level has been quantified using the modified STEAM sequence on 3T MRI. We enrolled 15 healthy volunteers and a group of 51 patients who experienced stroke for the first time and had a good prognosis. The patients with infarction were divided into three groups according to their scores by using the DSM-IV diagnostic criteria for major depressive disorder and the 17-item Hamilton Depression Rating Scale (HDRS). We studied the association between post-stroke depression and (1)H-MRS measurements in unaffected frontal lobes. Single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) was performed to assess N-acetylaspartate/creatine (NAA)/Cr, (Glu)/Cr, choline (Cho)/Cr, and myoinositol (mI)/Cr ratios in stroke patients. The 11 patients (21.5%) who met the criteria for depression and 9 patients (17.6%) who had a high score for HDRS, (>14) but were not depressed, had a significantly higher Glu/Cr ratio than patients who scored ≤14 on HDRS and control groups (p < 0.001). No differences were found in NAA/Cr, Cho/Cr, or mI/Cr between the groups after stroke. These findings suggest that post-stroke depression is accompanied by changes in glutamate levels in the frontal lobe.

Proton magnetic resonance spectroscopy in patients with symptomatic unilateral internal carotid artery / middle cerebral artery stenosis or occlusion

PURPOSE

To explore the value of proton magnetic resonance spectroscopy imaging ((1)H-MRSI) in patients with stenosis or occlusion of the internal carotid artery (ICA) / middle cerebral artery (MCA).

MATERIALS AND METHODS

Fifty noninfarcted patients with stenosis or occlusion of unilateral ICA/MCA were included in our study. In the meantime, 25 patients with cerebral infarction and 25 healthy control subjects were enrolled. All patients and healthy control subjects underwent (1)H-MRSI. Cerebral metabolic changes were studied in the noninfarcted patients and compared with the infarcted patients as well as healthy control subjects.

RESULTS

In 50 noninfarcted patients N-acetylaspartate (NAA) decreased and choline increased in the ischemic hemisphere compared with the contralateral side and control subjects. Lactate peaks were observed in 12 patients. The metabolic changes were relatively slight but were associated with metabolic disruption in infarcted patients. There were relationships between metabolic abnormalities and neurological status of the noninfarcted patients.

CONCLUSION

(1)H-MRSI can demonstrate abnormal metabolic changes in cerebral tissues with no infarction, while with ICA/MCA may show stenosis or occlusion at an early stage, which may help guide treatment decisions and preoperative evaluation.

Neuroimaging in acute ischaemic stroke: insights into unanswered questions of pathophysiology

The treatment of acute ischaemic stroke is based on the principle that there is ischaemic but still potentially salvageable tissue that could be rescued if blood flow could be restored quickly. It is assumed that salvage might only be possible in the first few hours, and that infarct expansion is a direct result of failed recanalization of the main artery. This concept arose from experimental work in the 1970s, supported more recently by studies using imaging to identify penumbral tissue. However, although magnetic resonance diffusion and perfusion imaging is a way of imaging penumbral tissue and has been around for over a decade, it is not an easy technique to apply in practice and its use has produced conflicting results. Computed tomography perfusion, and any other tissue perfusion imaging technique, is likely to encounter the same difficulties. Indeed many factors, other than the presence of a diffusion-perfusion mismatch acutely, may determine or influence ultimate tissue fate even days after the stroke, and in turn, clinical outcome. Many of these potential influences are beginning to emerge from studies using different forms of imaging at later times after stroke. This review will explore the information now emerging from imaging studies in large artery ischaemic stroke to summarize knowledge to date and indicate unresolved issues for the future.

Associations between diffusion and perfusion parameters, N-acetyl aspartate, and lactate in acute ischemic stroke

BACKGROUND AND PURPOSE

In acute ischemic stroke, the amount of neuronal damage in hyperintense areas on MR diffusion imaging (DWI) is unclear. We used spectroscopic imaging to measure N-acetyl aspartate (NAA, a marker of normal neurons) and lactate (a marker of ischemia) to compare with diffusion and perfusion values in the diffusion lesion in acute ischemic stroke.

METHODS

We recruited patients with acute ischemic stroke prospectively and performed MR diffusion weighted (DWI), perfusion, and spectroscopic imaging. We coregistered the images, outlined the visible diffusion lesion, and extracted metabolite, perfusion, and apparent diffusion coefficient (ADC) values from the diffusion lesion.

RESULTS

42 patients were imaged, from 1.5 to 24 hours after stroke. In the DWI lesion, although NAA was reduced, there was no correlation between NAA and ADC or perfusion values. However, raised lactate correlated with reduced ADC (Spearman rho=0.32, P=0.04) and prolonged mean transit time (MTT, rho=0.31, P=0.04). Increasing DWI lesion size was associated with lower NAA and higher lactate (rho=-0.44, P=0.003; rho=0.49, P=0.001 respectively); NAA fell with increasing times to imaging (rho=-0.3, P=0.03), but lactate did not change.

CONCLUSIONS

Although larger confirmatory studies are needed, the correlation of ADC and MTT with lactate but not NAA suggests that ADC and MTT are better markers of the presence of ischemia than of cumulative neuronal loss. Further studies should define more precisely the rate of neuronal loss and relationship to diffusion and perfusion parameters with respect to the depth and duration of ischemia.

Single voxel proton magnetic resonance spectroscopy in post-stroke depression

Mood disorders are associated with structural, metabolic and spectroscopic changes in prefrontal regions. In the case of depression associated with stroke, there is little information about the biochemical profile of these regions, as assessed by proton magnetic resonance spectroscopy ((1)H-MRS). In a group of first-ever stroke patients, we studied the association between post-stroke depression and (1)H-MRS measurements in unaffected frontal lobes. Twenty-six patients with a first ischemic stroke located outside the frontal lobes were included in the study. Single voxel proton magnetic resonance spectroscopy ((1)H-MRS) was performed to assess N-acetylaspartate/creatine (NAA)/Cr, glutamate+glutamine (Glx)/Cr, choline (Cho)/Cr and myo-inositol (mI)/Cr ratios. Patients were assessed within the first 10 days after stroke and again four months later. The diagnosis of depression was made on the basis of clinical observation, interview and Hamilton Depression Rating Scale scores. In a group of 26 patients, eight (31%) met criteria for depression at the first assessment, and nine (35%) met criteria for depression at follow-up. Patients with depression in the immediate post-stroke phase had significantly higher Glx/Cr ratios in the contralesional hemisphere than non-depressive patients. No biochemical differences were found between the groups at 4-month follow-up. These findings suggest that post-stroke depression is accompanied by changes in frontal lobe glutamate/glutamine levels, perhaps reflecting abnormalities in glutamatergic transmission in the immediate post-stroke period.

Detection of acute cytotoxic changes in progressive neuronal degeneration of childhood with liver disease (Alpers-Huttenlocher syndrome) using diffusion-weighted MRI and MR spectroscopy

Alpers-Huttenlocher syndrome (AHS) is a rare mitochondrial disorder of childhood onset that is characterized by progressive encephalopathy and hepatopathy. MRI studies are rare and have not added substantial information to the pathogenesis of the encephalopathy. Diffusion-weighted MRI (DWI) and MR spectroscopy (MRS) were used in a patient with AHS during acute clinical deterioration and after improvement. DWI detected signal hyperintensity in several brain areas not restricted to any vascular territory. MRS revealed an unequivocal lactate peak and a reduced N-acetyl-aspartate-creatinine (NAA/Crea) ratio. DWI signal hyperintensity was correlated with neurologic symptoms and decreased after clinical improvement. Potentially reversible neuronal cytotoxic edema resulting from acute impairment of mitochondrial function is strongly suggested to be an important pathogenetic mechanism in AHS encephalopathy.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.