Increased T2 Relaxation Time Research Articles

Language ability and hippocampal integrity

Studies of patients with temporal lobe epilepsy (TLE) have shown that aspects of language ability degeneration are associated with left hippocampal abnormalities[l], and in vivo studies of the normal human brain have demonstrated that the left hippocampus is active in some aspects of linguistic processing[2]. The aim of the present study was to investigate the relationship between performance on a battery of language tests involving object and word recognition and matching and hippocampal integrity as measured by T2 mapping in a cohort of patients with intractable TLE. Methods Forty three patients with TLE were divided into three groups according to hippocampal volume estimates obtained by using the Calvalieri method in combination with point counting on 3D Tl-weighted MR images. The 95th centiles of hippocampal volumes obtained by an identical approach in 35 controls provided normal limits for detection of medial temporal sclerosis (MTS). By this criterion, 15, 9, and 19 patients were assigned to left MTS, right MTS and no MTS respectively. T2 mapping of the anterior hippocampus was performed on all patients as a measure of hippocampal gliosis. A battery of computerised object matching, semantic matching and word-object matching tasks was used to assess specific aspects of language ability. The tasks required patients to match one of two source items with a target item based on object orientation, context and meaning. The computer automatically recorded accuracy and reaction times (RT). Results There were no overall differences between groups of patients on any of the language tasks. There were, however, significant correlations between anterior hippocampal T2 and aspects of language performance for the non MTS, but not the left and right MTS groups. In particular, for the no MTS group, there were significant positive correlations between left hippocampal T2 and mean RT on tests of object (.673, p=O.O02) and semantic matching (.496, p=O.O3), and corresponding correlations for sub-components of the word-object recognition test ranged from ,483 (p=O.O4) to ,676 (p=O.O03). Also, there was a significant negative correlation between right anterior hippocampal T2, (-531, p=O.O2; -.501, p=O.O4) and word-object matching. Discussion The results indicate that increased T2 relaxation time of left hippocampal tissue is related to language ability degeneration in the no MTS group. This concurs with the lateralisation evidence indicating that left hemispheric structures mediate linguistic processing, and that the hippocampus plays a role in this. The finding that these associations emerged only for the no MTS group may reflect the fact that T2 relaxation time is a reliable indicator of cognitive ability only for non-atrophied hippocampal tissue.

Secondary reduction in the apparent diffusion coefficient of water, increase in cerebral blood volume, and delayed neuronal death after middle cerebral artery occlusion and early reperfusion in the rat.

It has been reported recently that very delayed damage can occur as a result of focal cerebral ischemia induced by vascular occlusion of short duration. With use of diffusion-, T2-, and contrast-enhanced dynamic magnetic resonance imaging (MRI) techniques, the occlusion time dependence together with the temporal profile for this delayed response in a rat model of transient focal cortical ischemia have been established. The distal branch of the middle cerebral artery was occluded for 20, 30, 45, or 90 minutes. Twenty minutes of vascular occlusion with reperfusion exhibited no significant mean change in either the apparent diffusion coefficient of water (ADC) or the T2 relaxation time at 6, 24, 48, or 72 hours after reperfusion (P = 0.97 and 0.70, respectively). Ninety minutes of ischemia caused dramatic tissue injury at 6 hours, as indicated by an increase in T2 relaxation times to 135% of the contralateral values (P < 0.01). However, at intermediate periods of ischemia (30 to 45 minutes), complete reversal of the ADC was seen at 6 hours after reperfusion but was followed by a secondary decline over time, such that a 25% reduction in tissue ADC was seen at 24 as compared with 6 hours (P < 0.02). This secondary response was accompanied by an increase in cerebral blood volume (CBV), as shown by contrast-enhanced dynamic MRI (120% of contralateral values; P < 0.001), an increase in T2 relaxation time (132%; P < 0.01), together with clear morphological signs of cell death. By day 18, the mean volume of missing cortical tissue measured with high-resolution MRI in animals occluded for 30 and 45 minutes was 50% smaller than that in 90-minute occluded animals (P < 0.005). These data show that ultimate infarct size is reduced after early reperfusion and is occlusion time dependent. The early tissue recovery that is seen with intermediate occlusion times can be followed by cell death, which has a delayed onset and is accompanied by an increase in CBV.

Combined measurements of hippocampal N-acetyl-aspartate and T2 relaxation time in the evaluation of mesial temporal lobe epilepsy: correlation with clinical severity and memory performances.

In this study we tried to find a correlation between the clinical severity and memory performances, by comparing proton magnetic resonance (MR) spectroscopy and T2 relaxation time measurements in the hippocampi, in a homogeneous group of 27 patients with unilateral mesial temporal lobe epilepsy with ipsilateral hippocampal sclerosis on MR imaging, with a view to answer the following questions: (a) how sensitive is this approach for the assessment of the apparently normal contralateral hippocampus, (b) do the results relate to the clinical severity, and (c) does it allow evaluation of the degree of hippocampal dysfunction. Volume-selective proton MR spectroscopy of the head of both hippocampi was performed at 3 T, by using the PRESS sequence, with an echo time of 135 ms, to estimate NAA/(Cho + Cr) ratios. The relaxation times were measured at 0.28 T, by using a conventional Carr-Purcell-Meiboom-Gill sequence, with a repetition time of 2,000 ms, an echo time of 15 ms, and 48 echoes. The combination of NAA/(Cho + Cr) ratio and T2 relaxation time values was allowed to classify contralateral hippocampus abnormalities in two groups: first, decreased NAA/(Cho + Cr) ratio with strongly increased T2 relaxation time values corresponding to abnormalities observed in sclerotic ipsilateral hippocampi; and second, decreased NAA/(Cho + Cr) ratio with normal or slightly increased T2 relaxation time values. Whereas the NAA/(Cho + Cr) ratio or T2 relaxation time value alone was not correlated with memory performances, their association shows that left hippocampal injury evaluated both by NAA and T2 relaxation time measurements was clearly correlated with verbal memory scores, and right hippocampal injury, with visual memory scores. On the other hand, the maximal seizure frequency reported by the patients was correlated with ipsilateral NAA/(Cho + Cr) ratio and T2 relaxation time values but not with contralateral results. We showed that the combination of NAA and T2 relaxation time measurements can be used to examine the degree of ipsi- and contralateral hippocampal dysfunction or injuries and their relations with memory performances in the presurgical evaluation of patients.

Biophysical Linkage between MRI and EEG Coherence in Closed Head Injury

Using conventional MRI procedures, nuclear magnetic resonance (NMR) of brain water proton (1H)T2 relaxation times and EEG coherence were obtained from two independent groups of closed head injured (CHI) patients and a group of normal control subjects. Statistically significant intercorrelations were observed between1HT2 relaxation times of the cortical gray and white matter and EEG coherence. The analyses showed that lengthened1HT2 relaxation times of the cortical gray and white matter were related to: (1) decreased EEG coherence between short interelectrode distances (e.g., 7 cm) and increased EEG coherence between long interelectrode distances (e.g., 28 cm), (2) differences in EEG frequency in whichT2 relaxation time was most strongly related to the gray matter in the delta and theta frequencies in CHI patients, and (3) increasedT2 relaxation time and decreased short-distance EEG coherence were related to reduced cognitive function. The results were interpreted in terms of reduced integrity of protein/lipid neural membranes and the efficiency and effectiveness of short- and long-distance neural synchronization following traumatic brain injury.

Time and temperature dependence of MR parameters during thermal coagulation of ex vivo rabbit muscle.

Detailed measurements of the T1-weighted, T2-weighted, and MT-weighted signal were performed for ex vivo muscle samples heated to various temperatures for different times. Consistent, monotonic increases in signal intensity were observed with progressive thermal coagulation, corresponding to an increase in T2 relaxation time and an increase in MT-weighted signal for temperatures above 60 degrees C. The relationship for T1 relaxation was more complex, showing a decrease in T1 relaxation from 40 to 60 degrees C and an increase above 60 degrees C. These techniques provide a more direct measure of tissue thermal coagulation than that provided by MR thermometry and suggest MR imaging strategies for the optimization and monitoring of thermal coagulation therapy protocols that create thermal damage in target tissues.

Magnetic resonance imaging of isolated skeletal muscles. Osmotic influence.

The authors evaluate the contribution of intracellular water to the change of T2 relaxation time. Magnetic resonance images of frog muscles (n = 16) were obtained in hypotonic, isotonic, and hypertonic solutions, and their leg weights and T2 relaxation times were measured. Likewise, these values were measured after electric stimulation for 2 to 10 minutes in isotonic solution (n = 5). The muscle weights increased in the hypotonic solutions, whereas they showed no change in isotonic solution. T2 relaxation times, however, showed little change in either isotonic or hypotonic solutions. In electrically stimulated muscles, T2 relaxation times increased, accompanying the increase in muscle weight in isotonic solutions. Muscle contraction results in increased T2 relaxation time, but intracellular water hardly contributes to the increase in this value. Therefore, an increase in extracellular water may be the main cause of the increase in T2 relaxation time seen in exercised muscles.

Magnetic Resonance Imaging Evidence of Decreased Putamenal Iron Content in Idiopathic Parkinson's Disease

To determine the changes in basal ganglia iron content associated with various stages of idiopathic Parkinson's disease. Prospective magnetic resonance imaging study using a 2-T magnet. Ambulatory care referral center. Forty-five patients suffering from levodopa-responsive Parkinson's disease and 45 age-matched controls. The T2 relaxation time calculated in various regions of the basal ganglia, the duration of Parkinson's disease, and the age of subjects. Patients with Parkinson's disease exhibited significantly decreased T2 relaxation time in the pars compacta of the substantia nigra compared with controls (P < .01), regardless of disease duration. Patients with a duration of illness above 10 years (n = 12) exhibited significantly increased T2 relaxation time in the anterior and posterior putamen (P < .005 and P < .01, respectively) and in the pallidum (P < .05) compared with age-matched controls. Putamental T2 relaxation time positively correlated with disease duration (P < .05). These results suggest that more complex brain iron changes than those previously reported are associated with idiopathic Parkinson's disease, including increased nigral iron content and decreased putamenal and pallidal iron concentration in patients with a duration of illness above 10 years.

Vigabatrin-induced lesions in the rat brain demonstrated by quantitative magnetic resonance imaging

Rats treated with 250 mg/kg/day vigabatrin showed lesions detected by magnetic resonance imaging (MRI) in the cerebellar white matter in vivo. No lesions were seen in any control animal. As well as these visually apparent lesions, quantitative T2 relaxation time measurements showed a 12 ms increase in cerebellar white matter from 66 ± 4 ms (SD, n = 5) to 78 ± 2 ms (SD, n = 7). This region, as expected from previous studies, showed microvacuolation on postmortem pathology. Additionally, significant increases in T2 relaxation times of 4–9 ms were found in the cerebral cortex, thalamus and hippocampus. Microvacuolation was not detected by post-mortem histopathology in the cerebral cortex or hippocampus, however, immunohistochemical staining for glial fibrillary acidic protein and for macrophages (EDI) showed reactive astrocytes (gliosis) and in more severe cases, microglial proliferation in these regions; such changes were also seen in association with the microvacuoles. No T2 increase was found in the cerebellar grey matter or olfactory bulbs. MRI techniques, including T2 relaxometry, are therefore sensitive for detecting vigabatrin-induced changes, including reactive astrocytosis, microglial proliferation and vacuolation in the rat brain. These results suggest that quantitative MRI should be a useful method for evaluating whether vigabatrin has neuropathological effects when given to patients.

Microneurosurgical treatment of intracranial dermoid and epidermoid tumors.

Forty-three patients with intracranial, intradural dermoid (8) and epidermoid (35) tumors underwent radical surgical resection utilizing strict microneurosurgical technique. The average age was 37.3 years for the patients with epidermoid tumors and 36.2 years for the patients with dermoid tumors. The male to female ratio was 3:2 for the epidermoid group and 3:1 for the dermoid group. Common clinical presentations included cerebellar dysfunction, cranial nerve impairment, and seizures. Typically, computed tomography scans revealed the epidermoid tumors (30 cases studied) as nonhomogeneous hypodense lesions with irregular borders and without contrast enhancement. The dermoid tumors (7 cases studied) had a similar appearance, but with a wider range of attenuation values. Magnetic resonance imaging findings for the epidermoid tumors (6 cases studied) consisted of increased T1 and increased T2 relaxation times. Supratentorial tumors were excised by the pterional (frontosphenotemporal) approach, mesencephalic tumors by either a supratentorial posterior interhemispheric transtentorial approach or an infratentorial/supracerebellar method, and posterior fossa tumors by either a medially or laterally positioned suboccipital osteoplastic craniotomy. One epidermoid tumor and one dermoid tumor were considered to be subtotally resected because of dense adherences left attached to vital structures; the remaining 41 tumors were completely excised. The most frequent complications were aseptic/chemical meningitis and transient cranial nerve palsies. There were no perioperative deaths. Mean follow-up was 5.2 years. Eighty-six percent of patients reported good to excellent results. No patient had experienced symptomatic or radiographic evidence of recurrence.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear magnetic resonance imaging of acute myocardial infarction in dogs: Alterations in magnetic relaxation times

Nuclear magnetic resonance (NMR) imaging was used to study 24-hour-old acute myocardial infarctions in 8 dogs. Images and measurements of excised hearts were obtained in a 6.5 ml bore-resistive NMR imager (0.35 Tesla). Spin echo NMR imaging in each instance demonstrated the area of infarction as a region of increased signal intensity compared with that in normal myocardium. The T1 and T2 values of the area of infarction were greater than those of normal myocardium in all dogs. For each dog the T1 value was greater for the infarct region; however, the group mean value for T1 (ms) of the infarct region (728 ± 94) was not significantly greater than that for the normal region (650 ± 87). The T2 value (ms) was discriminate for all dogs, and the mean value for the infarct region (48 ± 2) was significantly different (p < 0.01) from the value for normal myocardium (42 ±1). The percent water content of the infarct (79 ± 1%) was significantly greater (p < 0.01) than that of normal regions (76 ± 1 %). The linear relationship between T2 value and percent water content showed a good correlation coefficient (r = 0.90; p < 0.01). NMR imaging detects acute myocardial infarction as a positive image without contrast media. Increased signal intensity of the infarct is related to increased hydrogen density and increased T2 relaxation time.