Time course of NAA T2 and ADC(w) in ischaemic stroke patients: 1H MRS imaging and diffusion-weighted MRI

Background and purpose: Proton spectroscopy and quantitative diffusion-weighted imaging (DWI) were used to investigate the pertinence of N-acetyl aspartate (NAA) as a reliable marker of neuronal density in human stroke. Methods: The time courses of tissue water apparent diffusion coefficient (ADC_w) and metabolite T2 were investigated on a plane corresponding to the largest area of cerebral infarction, within and outside the site of infarction in 71 patients with a large cortical middle cerebral artery territory infarction. Results: Significant reductions are seen in NAA T2 deep within the infarction during the period comprised between 5 and 20 days postinfarction; the relaxation times appearing to normalise several months after stroke. After an acute reduction in ADC_w, the pseudonormalisation of ADC_w occurs at 8–12 days after the ischaemic insult. The minimum in N-acetyl aspartate T2 relaxation times and the pseudonormalisation of ADC_w appear to coincide. Conclusions: The data suggest that modifications in the behaviour of the observed proton metabolites occur during the period when the vasogenic oedema is formed and cell membrane integrity is lost. For this reason, NAA may not be a reliable marker of neuronal density during this period.     

Natural history of Canavan disease revealed by proton magnetic resonance spectroscopy (1H-MRS) and diffusion-weighted MRI

Canavan disease is a childhood leukodystrophy caused by mutations in the gene for human aspartoacylase ( ASPA), which leads to an abnormal accumulation of the substrate molecule N-acetyl-aspartate (NAA) in the brain. This study was designed to model the natural history of Canavan disease using MRI and proton magnetic resonance spectroscopy ( (1)H-MRS). NAA and various indices of brain structure (morphology, quantitative T1, fractional anisotropy, apparent diffusion coefficient) were measured in white and gray matter regions during the progression of Canavan disease. A mixed-effects statistical model was used to fit all outcome measures. Longitudinal data from 28 Canavan patients were directly compared in each brain region with reference data obtained from normal, age-matched pediatric subjects. The resultant model can be used to non-invasively monitor the natural history of Canavan disease or related leukodystrophies in future studies involving drug, gene therapy, or stem cell treatments.     

Comparison of diffusion-weighted MRI and CT in acute stroke

OBJECTIVE: To compare diffusion-weighted MRI (DWI) and CT with respect to accuracy of localizing acute cerebral infarction; sensitivity, specificity, and interrater reliability for identifying more than one-third middle cerebral artery (MCA) territory involvement; and correlation of acute lesion volume with final infarct volume. METHOD: Nineteen consecutive stroke patients underwent CT and DWI within 7 hours of stroke onset and a follow-up DWI examination 36 hours after symptom onset, which served as the "gold standard" for lesion location and extent of MCA involvement. Each scan was evaluated for acute ischemic lesions by two experienced observers. After 30 days, T2-weighted MRI was obtained for assessment of the final infarct volume. RESULTS: The acute CT and DWI scans were obtained on average 2.6 and 5.1 hours after symptom onset. On DWI the acute lesion was identified correctly in all instances and on CT it was identified correctly in 42 to 63% of patients. Sensitivity for detection of more than 33% MCA involvement was better for DWI (57 to 86%) than for CT (14 to 43%), whereas specificity was excellent for both. Interrater reliability was moderately good for both (kappa, 0.6 for DWI; 0.5 for CT). A positive correlation (r = 0.79; p = 0.001) existed between lesion volume on acute DWI and final infarct volume, whereas no correlation was found between CT volume and final infarct volume. CONCLUSION: When compared with CT, DWI was more accurate for identifying acute infarction and more sensitive for detection of more than 33% MCA involvement. In addition, lesion volume on acute DWI, but not on acute CT, correlated strongly with final infarct volume. Additional studies are required to demonstrate whether these advantages of DWI are clinically relevant in the management of patients with acute stroke.     

In vivo 1H magnetic resonance spectroscopy, T2-weighted and diffusion-weighted MRI during lithium-pilocarpine-induced status epilepticus in the rat

Temporal lobe epilepsy (TLE) is associated with febrile convulsions and childhood status epilepticus (SE). Since the initial precipitating injury, triggering epileptogenesis, occurs during this SE, we aimed to examine the metabolic and morphological cerebral changes during the acute phase of experimental SE noninvasively. In the rat lithium-pilocarpine model of SE, we performed quantified T(2)- and isotropic-diffusion-weighted (DW) magnetic resonance imaging (MRI) at 3 and 5 h of SE and acquired single-voxel (1)H MR spectra at 2, 4 and 6 h of SE. T(2) was globally decreased, most pronounced in the amygdala (Am) and piriformic cortex (Pi), in which also a significant decrease in apparent diffusion coefficient (ADC) was found. In contrast, ADC values increased transiently in the hippocampus (HC) and thalamus (Th). MR spectra showed a decrease in N-acetylaspartate (NAA) and choline (Cho) and an increase of lactate in a hippocampal voxel. The T(2) decrease, attributed to raised deoxyhemoglobin, and the presence of lactate both indicate a mismatch between oxygen demand and delivery. The ADC decrease, indicative of excitotoxicity, confirms that the amygdala and piriformic cortex are particularly vulnerable to lithium-pilocarpine-induced seizures. The transient ADC increase in the thalamus may reflect the breakdown of the blood-brain barrier (BBB), which is shown to occur in this region at these time points. Neuronal damage and failure of energy-dependent formation of NAA are likely causes of an observed decrease in NAA, while the decrease in Cho is possibly due to depletion of the cholinergic system. This study illustrates that relative hypoxia, excitotoxicity and concomitant neuronal damage associated with SE can be probed noninvasively with MR. These pathological phenomena are the first to contribute to the pathophysiology of spontaneous recurrent seizures in a later stage in this animal model.     

Valproate-induced encephalopathy: assessment with MR imaging and 1H MR spectroscopy

The anticonvulsant agent valproate (VPA) may cause hyperammonemic encephalopathy. Magnetic resonance imaging (MRI) and proton MR spectroscopic (MRS) findings in a patient with VPA-induced hyperammonemic encephalopathy are described. MRI showed a metabolic-toxic lesion pattern with bilateral T2-hyperintense lesions in the cerebellar white matter and in the globus pallidus. MR spectroscopic findings were indistinguishable from hepatic encephalopathy with severe depletion of myoinositol and choline and with glutamine excess. N-Acetylaspartate levels were moderately decreased. Quantitative MRS gave detailed insight into alterations of brain metabolism in VPA-induced encephalopathy.     

Pregabalin suppresses calcium-mediated proteolysis and improves stroke outcome

Pregabalin, a Ca(2+) channel α(2)δ-subunit antagonist with analgesic and antiepileptic activity, reduced neuronal loss and improved functional outcome in a mouse model of focal ischemic stroke. Pregabalin administration (5-10mg/kg, i.p.) 30-90 min after transient middle cerebral artery occlusion/reperfusion reduced infarct volume, neuronal death in the ischemic penumbra and neurological deficits at 24h post-stroke. Pregabalin significantly decreased the amount of Ca(2+)/calpain-mediated α-spectrin proteolysis in the cerebral cortex measured at 6h post-stroke. Together with the extensive clinical experience with pregabalin for other neurological indications, our findings suggest the potential for a therapeutic benefit of pregabalin in stroke patients.     

Microembolic signals within 24 hours of stroke onset and diffusion-weighted MRI abnormalities

BACKGROUND: The clinical relevance of the microembolic signals (MES) detected by transcranial Doppler sonography (TCD) in acute stroke remains unclear. In a prospective study the authors analyzed the relationship between MES and the findings on diffusion-weighted magnetic resonance imaging (DWI) in acute stroke patients. METHODS: We performed TCD for a period of 30 min to detect MES in patients within 24 h of stroke onset, and DWI was done within the initial 7 days. MES were assessed from Doppler waves obtained from the middle cerebral artery contralateral to the side of the neurological deficits. The acute ischemic lesions observed on DWI were classified by their diameter (small, medium or large) and by their site (cortical, superficial perforator territory, internal borderzone or deep perforator territory). RESULTS: We obtained Doppler waves from 39 vessels in 37 patients; 2 patients had bilateral deficits. MES were detected in 12 vessels (MES-positive group) and not detected in 27 vessels (MES-negative group). No significant differences in clinical features were observed between the 2 groups. The number of small lesions was significantly higher in the MES-positive group than in the MES-negative group (p = 0.02). The numbers of cortical and superficial perforator infarcts were significantly higher in the MES-positive group than in the MES-negative group (p = 0.002 and 0.02, respectively). CONCLUSION: In acute ischemic stroke, MES detected by TCD in the acute phase may produce small cortical and subcortical lesions found on DWI.     

Proton MR spectroscopy and diffusion-weighted MR imaging for the diagnosis of intracranial tuberculomas. Report of two cases

With the current prevalence of tuberculosis, the incidence of intracranial tuberculoma may be on the rise in industrialized nations. However, clinical findings suggestive of systemic tuberculosis are frequently subtle or absent in patients with intracranial tuberculoma, and no specific neuroradiologic characteristics of tuberculoma have been defined as yet. We report two cases of ring-enhanced intracranial tuberculoma in which magnetic resonance (MR) proton spectroscopy and diffusion-weighted (DW) imaging were useful in the differential diagnosis between tuberculoma and other ring-enhanced mass lesions. Pulmonary tuberculosis had been diagnosed in one patient, but radiologic lung study and tuberculin skin test were negative in the other. DW imaging showed bright signal intensity in the core of all lesions in both patients. Malignant gliomas and metastatic brain tumors do not have this characteristic. Proton MR spectroscopy of lesion cores showed lipid peaks and a choline peak in one, and a lipid/lactate mixture pattern in the other, which differed distinctively from those of the pyogenic brain abscess. in each case, one lesion was surgically removed. Antituberculosis drugs were started before surgery for one patient and after surgery for the other. In both, the remaining lesions were reduced significantly in size. We discuss the diagnostic potential of these MR techniques and management options of intracranial tuberculoma.     

Proton MR spectroscopy and diffusion-weighted MR imaging for the diagnosis of intracranial tuberculomas. Report of two cases

Abstract

With the current prevalence of tuberculosis, the incidence of intracranial tuberculoma may be on the rise in industrialized nations. However, clinical findings suggestive of systemic tuberculosis are frequently subtle or absent in patients with intracranial tuberculoma, and no specific neuroradiologic characteristics of tuberculoma have been defined as yet. We report two cases of ring-enhanced intracranial tuberculoma in which magnetic resonance (MR) proton spectroscopy and diffusion-weighted (DW) imaging were useful in the differential diagnosis between tuberculoma and other ring-enhanced mass lesions. Pulmonary tuberculosis had been diagnosed in one patient, but radiologic lung study and tuberculin skin test were negative in the other. DW imaging showed bright signal intensity in the core of all lesions in both patients. Malignant gliomas and metastatic brain tumors do not have this characteristic. Proton MR spectroscopy of lesion cores showed lipid peaks and a choline peak in one, and a lipid/lactate mixture pattern in the other, which differed distinctively from those of the pyogenic brain abscess. In each case, one lesion was surgically removed. Antituberculosis drugs were started before surgery for one patient and after surgery for the other. In both, the remaining lesions were reduced significantly in size. We discuss the diagnostic potential of these MR techniques and management options of intracranial tuberculoma. [Neurol Res 2002; 24: 537-543]     

A review of 1H MR spectroscopy findings in Alzheimer's disease

Hydrogen-1 MR spectroscopy (MRS) studies demonstrate metabolic differences between patients who have Alzheimer's disease (AD) and cognitive normal age-matched controls. Clinical MRS also shows regional variations in metabolites between patients who have AD and those who have other dementias. Single-voxel and volumetric standard MRS techniques and automated data processing software are available for clinical MR scanners. Improvements in specificity and sensitivity of AD diagnosis, using MRS techniques as an adjunct to clinical imaging, are under evaluation. Multiparametric data analyses show, however, that metabolite changes correlate with in-vitro, postmortem, and metabolic changes and to changes in or predictions of cognitive scores.     

MR imaging, diffusion-weighted imaging and MR spectroscopy findings in acute rapidly progressive subacute sclerosing panencephalitis

We are presenting two cases with subacute sclerosing panencephalitis of acute and rapid form, which were initially diagnosed as acute viral encephalitis. We obtained both diffusion-weighted imaging and magnetic resonance spectroscopy, whose findings suggested the presence of acute inflammatory and metabolic changes with peculiar distribution, which were not observed on conventional MR imaging. These techniques might help to demonstrate the extent and progression of the panencephalitis.     

Quantitative 1H magnetic resonance spectroscopy and MRI of Parkinson's disease.

Magnetic resonance imaging (MRI) and (1)H magnetic resonance spectroscopy (MRS) of the substantia nigra, basal ganglia, and cerebral cortex were performed on 10 patients with Parkinson's disease (PD) and 13 age-matched, healthy control subjects. Compared to controls, PD patients had approximately 24% lower creatine in the region of the substantia nigra and smaller volumes of the putamen (11%), globus pallidus (16%), and prefrontal cortex (6%; all P < 0.05). No other significant between-group differences were found in nine regions examined. Thus, quantitative MRI may show regional neurodegenerative changes outside the substantia nigra in PD but PD-linked extranigral metabolic abnormalities, if they exist, may be difficult to detect with current (1)H MRS methods. In additional, exploratory tests, volumes of the caudate (r = -0.56), putamen (r = -0.66), and globus pallidus (r = -0.60; all P < 0.05) were negatively correlated with the volume of the substantia nigra pars compacta in controls. In PD these correlations did not hold. Instead, pallidal volume in PD was positively correlated with compacta volume (r = 0.64; P < 0.05). This relationship suggests that basal ganglia volumes may be influenced by dopaminergic innervation from the substantia nigra in normal and PD subjects.     

(1)H magnetic resonance spectroscopy of autosomal ataxias

Multiple forms of autosomal ataxia exist which can be identified by genetic testing. Due to their wide variety, the identification of the appropriate genetic test is difficult but could be aided by magnetic resonance data. In this study, magnetic resonance spectroscopy (MRS) and imaging (MRI) data were recorded for 20 ataxia patients of six different types and compared to 20 normal subjects. Spectra were acquired in the pons, left frontal lobe, left basal ganglia, left cerebellar hemisphere and vermis. Both metabolite spectra and absolute metabolite concentrations were determined. Differences in metabolite levels were observed between ataxia patients and control subjects and between ataxia patients of different types. A number of correlations were found between metabolite ratios, atrophy levels, number of repeats on the small and large allele, age at examination, symptoms duration and age at symptoms onset for ataxia patients. These MR characteristics are expected to be useful for the identification of the ataxia type.     

Assessing the outcome of stroke: a comparison between MRI and clinical stroke scales

OBJECTIVES: To assess the correlation of diffusion-weighted (DWI) and perfusion-weighted imaging (PWI) findings with the severity of acute neurologic deficit and their ability to predict short and long-term clinical outcomes of stroke. The ability of DWI and PWI to predict the outcome was compared with the ability of clinical stroke scales to predict the outcome. METHODS: Forty-eight patients with acute stroke underwent diffusion DWI and PWI on the first and eighth day after the ictus. Clinical and functional scales were carried out before each scan and 3 months after the stroke. RESULTS: The volumes of both the DWI and the PWI lesions correlated well with the acute neurologic deficit and the final outcome. The first day PWI (r = 0.64) and the National Institutes of Health Stroke Scale (NIHSS) scores (r = 0.70) correlated well with the final outcome. However, in logistic regression analysis, only the NIHSS score at the acute stage was the only independent predictor of the long-term clinical outcome. CONCLUSION: While the PWI and DWI lesion volumes correlated well with the outcome of the stroke, the imaging measurements did not improve the prognostic power over plain clinical stroke scale scores.     

质子磁共振波谱在胶质瘤诊断中的应用

目的 研究质子磁共振波谱（1H Magnetic Resonance Spectroscopy,1HMRS）在胶质瘤诊断及分级中的应用。方法搜集行1HMRS检查并经病理证实的36例胶质瘤患者,其中A组星形胶质细胞瘤Ⅰ～Ⅱ级21例,B组星形胶质细胞瘤Ⅲ～Ⅳ级和多形性胶质母细胞瘤15例。对侧部位的结果作内对照组。观察氮乙酰门氡氨酸（N—acetylaspartate,NAA）、胆碱（choline,Cho）、肌酸（creatine,Cr）、肌醇（Ins）的共振峰及比值。结果A组同对照组间NAA／Cr、NAA／Cho、Cho／Cr差异有统计意义（P〈0．05）。B组同对照组间NAA／Cr、NAA／Cho、Cho／Cr差异有统计意义（P％0．05）。A组与B组间NAA／Cr和NAA／Cho差异有统计意义（P〈0．05）。结论 1HMRS可提高对胶质瘤诊断和分级的准确性。