Functional Reorganization Associated with Semantic Language Processing in Temporal Lobe Epilepsy Patients after Anterior Temporal Lobectomy : A Longitudinal Functional Magnetic Resonance Image Study

OBJECTIVE: The focus of this study is brain plasticity associated with semantic aspects of language function in patients with medial temporal lobe epilepsy (mTLE). METHODS: Using longitudinal functional magnetic resonance imaging (fMRI), patterns of brain activation were observed in twelve left and seven right unilateral mTLE patients during a word-generation task relative to a pseudo-word reading task before and after anterior temporal section surgery. RESULTS: No differences were observed in precentral activations in patients relative to normal controls (n = 12), and surgery did not alter the phonological-associated activations. The two mTLE patient groups showed left inferior prefrontal activations associated with semantic processing (word-generation > pseudo-word reading), as did control subjects. The amount of semantic-associated activation in the left inferior prefrontal region was negatively correlated with epilepsy duration in both patient groups. Following temporal resection, semantic-specific activations in inferior prefrontal region became more bilateral in left mTLE patients, but more left-lateralized in right mTLE patients. The longer the duration of epilepsy in the patients, the larger the increase in the left inferior prefrontal semantic-associated activation after surgery in both patient groups. Semantic activation of the intact hippocampus, which had been negatively correlated with seizure frequency, normalized after the epileptic side was removed. CONCLUSION: These results indicate alternation of semantic language network related to recruitment of left inferior prefrontal cortex and functional recovery of the hippocampus contralateral to the epileptogenic side, suggesting an intra- and inter-hemispheric reorganization following surgery.

Principle and Recent Advances of Neuroactivation Study / 핵의학분자영상

Among the nuclear medicine imaging methods available today, H215O-PET is most widely used by cognitive neuroscientists to examine regional brain function via the measurement of regional cerebral blood flow (rCBF). The short half-life of the radioactively labeled probe, 15O, often allows repeated measures from the same subjects in many different task conditions. H215O-PET, however, has technical limitations relative to other methods of functional neuroimaging, e.g., fMRI, including relatively poor time and spatial resolutions, and, frequently, insufficient statistical power for analysis of individual subjects. However, recent technical developments, such as the 3-D acquisition method provide relatively good image quality with a smaller radioactive dosage, which in turn results in more PET scans from each individual, thus providing sufficient statistical power for the analysis of individual subject's data. Furthermore, the noise free scanner environment H215O PET, along with discrete acquisition of data for each task condition, are important advantages of PET over other functional imaging methods regarding studying state-dependent changes in brain activity. This review presents both the limitations and advantages of 15O-PET, and outlines the design of efficient PET protocols, using examples of recent PET studies both in the normal healthy population, and in the clinical population.

Functional MRI Study for Phonological and Semantic Language Processing in Strongly Right-Handed Korean Twenty Year Olds / 대한간질학회지

OBJECTIVE: Using functional magnetic resonance imaging, cerebral language areas were determined during a series of language tasks in normal strong right-handed subjects. METHODS: Twelve normal right-handed volunteers were examined on a 1.5T MR unit. Language task paradigms included two phonological tasks involving meaningless letters and sentences, and four semantic tasks using different types of words. Each language task was examined using a separate scan consisted of three blocks separated by rest periods. BOLD (blood oxygenation level dependent) signals during language tasks were compared using 24 sec alternating rest periods during which subjects concentrated on a plus symbol. After preprocessing and statistically analyzing individual data, group analysis (p<0.001, k=50) was performed using SPM99 software. RESULTS: Meaningless letter reading was more efficient than sentence reading, in terms of delineating brain regions related to phonological processing, we found significant regions in the left inferior frontal gyrus (IFG), left thalamus, bilateral cingulate gyri, right anterior superior temporal gyrus (STG), right IFG, and left inferior parietal lobule (IPL). During semantic tasks, left IFG, left posterior middle temporal gyrus, left IPL, bilateral medial frontal gyrus, right posterior STG, right parahippocampal, and fusiform gyri were found to be activated. CONCLUSION: During the two phonological tasks, normal strongly right-handed people more actively used the left IFG, right anterior temporal lobe, and right IFG than during semantic processing, whereas during the four semantic tasks, these subjects more actively used the bilateral posterior temporal and right medial temporal lobes.

Effects of Motion Correction for Dynamic 11CRaclopride Brain PET Data on the Evaluation of Endogenous Dopamine Release in Striatum / 대한핵의학회잡지

PURPOSE: Neuroreceptor PET studies require 60-120 minutes to complete and head motion of the subject during the PET scan increases the uncertainty in measured activity. In this study, we investigated the effects of the data-driven head motion correction on the evaluation of endogenous dopamine release (DAR) in the striatum during the motor task which might have caused significant head motion artifact. MATERIALS AND METHODS: [11C]raclopride PET scans on 4 normal volunteers acquired with bolus plus constant infusion protocol were retrospectively analyzed. Following the 50 min resting period, the participants played a video game with a monetary reward for 40 min. Dynamic frames acquired during the equilibrium condition (pre-task: 30-50 min, task: 70-90 min, post-task: 110-120 min) were realigned to the first frame in pre-task condition. Intra-condition registrations between the frames were performed, and average image for each condition was created and registered to the pre-task image (inter-condition registration). Pre-task PET image was then co-registered to own MRI of each participant and transformation parameters were reapplied to the others. Volumes of interest (VOI) for dorsal putamen (PU) and caudate (CA), ventral striatum (VS), and cerebellum were defined on the MRI. Binding potential (BP) was measured and DAR was calculated as the percent change of BP during and after the task. SPM analyses on the BP parametric images were also performed to explore the regional difference in the effects of head motion on BP and DAR estimation. RESULTS: Changes in position and orientation of the striatum during the PET scans were observed before the head motion correction. BP values at pre-task condition were not changed significantly after the intra-condition registration. However, the BP values during and after the task and DAR were significantly changed after the correction. SPM analysis also showed that the extent and significance of the BP differences were significantly changed by the head motion correction and such changes were prominent in periphery of the striatum. CONCLUSION: The results suggest that misalignment of MRI-based VOI and the striatum in PET images and incorrect DAR estimation due to the head motion during the PET activation study were significant, but could be remedied by the data-driven head motion correction.

Development of Korean Standard Brain Templates

We developed age, gender and ethnic specific brain templates based on MR and Positron-Emission Tomography (PET) images of Korean normal volunteers. Seventy-eight normal right-handed volunteers (M/F=49/29) underwent 3D T1-weighted SPGR MR and F-18-FDG PET scans. For the generation of standard templates, an optimal target brain that has the average global hemispheric shape was selected for each gender. MR images were then spatially normalized by linear transformation to the target brains, and normalization parameters were reapplied to PET images. Subjects were subdivided into 2 groups for each gender: the young/midlife (<55 yr) and the elderly groups. Young and elderly MRI/PET templates were composed by averaging the spatially normalized images. Korean templates showed different shapes and sizes (mean length, width, and height of the brains were 16.5, 14.3 and 12.1 cm for man, and 15.6, 13.5 and 11.4 cm for woman) from the template based on Caucasian (18.3, 14.2, and 13.3 cm). MRI and PET templates developed in this study will provide the framework for more accurate stereotactic standardization and anatomical localization.

Voxel-based Morphometry (VBM) Based Assessment of Gray Matter Loss in Medial Temporal Lobe Epilepsy: Comparison with FDG PET / 대한핵의학회잡지

PURPOSE: The aims of this study were to find brain regions in which gray matter volume was reduced and to show the capability of voxel-based morphometry (VBM) analysis for lateralizing epileptogenic zones in medial temporal lobe epilepsy (mTLE). The findings were compared with fluorodeoxyglucose positron emission tomography (FDG PET). MATERIALS AND METHODS: MR T1-weighted images of 12 left mTLE and 11 right mTLE patients were compared with those of 37 normal controls. Images were transformed to standard MNI space and averaged in order to create study-specific brain template. Each image was normalized to this local template and brain tissues were segmented. Modulation VBM analysis was performed in order to observe gray matter volume change. Gray matter was smoothed with a Gaussian kernel. After these preprocessing, statistical analysis was performed using statistical parametric mapping software (SPM99). FDG PET images were compared with those of 22 normal controls using SPM. RESULTS: Gray matter volume was significantly reduced in the left amygdala and hippocampus in left mTLE. In addition, volume of cerebellum, anterior cingulate, and fusiform gyrus in both sides and left insula was reduced. In right mTLE, volume was reduced significantly in right hippocampus. In contrast, FDG uptake was decreased in broad areas of left or right temporal lobes in left TLE and right TLE, respectively. CONCLUSIONS: Gray matter loss was found in the ipsilateral hippocampus by modulation VBM analysis in medial temporal lobe epilepsy. This VBM analysis might be useful in lateralizing the epileptogenic zones in medial temporal lobe epilepsy, while SPM analysis of FDG PET disclosed hypometabolic epileptogenic zones.

Quantification of Brain Images Using Korean Standard Templates and Structural and Cytoarchitectonic Probabilistic Maps / 대한핵의학회잡지

PURPOSE: Population based structural and functional maps of the brain provide effective tools for the analysis and interpretation of complex and individually variable brain data. Brain MRI and PET standard templates and statistical probabilistic maps based on image data of Korean normal volunteers have been developed and probabilistic maps based on cytoarchitectonic data have been introduced. A quantification method using these data was developed for the objective assessment of regional intensity in the brain images. Materials and METHODS: Age, gender and ethnic specific anatomical and functional brain templates based on MR and PET images of Korean normal volunteers were developed. Korean structural probabilistic maps for 89 brain regions and cytoarchitectonic probabilistic maps for 13 Brodmann areas were transformed onto the standard templates. Brain FDG PET and SPGR MR images of normal volunteers were spatially normalized onto the template of each modality and gender. Regional uptake of radiotracers in PET and gray matter concentration in MR images were then quantified by averaging (or summing) regional intensities weighted using the probabilistic maps of brain regions. Regionally specific effects of aging on glucose metabolism in cingulate cortex were also examined. RESULTS: Quantification program could generate quantification results for single spatially normalized images per 20 seconds. Glucose metabolism change in cingulate gyrus was regionally specific: ratios of glucose metabolism in the rostral anterior cingulate vs. posterior cingulate and the caudal anterior cingulate vs. posterior cingulate were significantly decreased as the age increased. 'Rostral anterior'/ 'posterior' was decreased by 3.1% per decade of age (P< 10 (-11), r=0.81) and 'caudal anterior'/ 'posterior' was decreased by 1.7% (P< 10 (-8), r=0.72). CONCLUSION: Ethnic specific standard templates and probabilistic maps and quantification program developed in this study will be useful for the analysis of brain image of Korean people since the difference in shape of the hemispheres and the sulcal pattern of brain relative to age, gender, races, and diseases cannot be fully overcome by the nonlinear spatial normalization techniques.

Application of False Discovery Rate Control in the Assessment of Decrease of FDG Uptake in Early Alzheimer Dementia / 대한핵의학회잡지

PURPOSE: Determining an appropriate thresholding is crucial for PDG PET analysis since strong control of Type I error could fail to find pathological differences between early Alzheimer' disease (AD) patients and healthy normal controls. We compared the SPM results on FDG PET imaging of early AD using uncorrected p-value, random-field based corrected p-value and false discovery rate (FDR) control. MATERIALS AND METHODS: Twenty-eight patients (66+/-7 years old) with early AD and 18 age-matched normal controls (68+/-6 years old) underwent FDG brain PET. To identify brain regions with hypo-metabolism in group or individual patient compared to normal controls, group images or each patient's image was compared with normal controls using the same fixed p-value of 0.001 on uncorrected thresholding, random-field based corrected thresholding and FDR control. RESULTS: The number of hypo-metabolic voxels was smallest in corrected p-value method, largest in uncorrected p-value method and intermediate in FDG thresholding in group analysis. Three types of result pattern were found. The first was that corrected p-value did not yield any voxel positive but FDR gave a few significantly hypometabolic voxels (8/28, 29%). The second was that both corrected p-value and FDR did not yield any positive region but numerous positive voxels were found with the threshold of uncorrected p-values (6/28, 21%). The last was that FDR was detected as many positive voxels as uncorrected p-value method (14/28, 50%). CONCLUSIONS: FDR control could identify hypo-metabolic areas in group or individual patients with early AD. We recommend FDR control instead of uncorrected or random-field corrected thresholding method to find the areas showing hypometabolism especially in small group or individual analysis of FDG PET.