A Study of Optimal SOAmin for Motor and Language Tasks in Event-related fMRl using Stochastic Design

PURPOSE: The minimum stimulus onset asynchronoy(SOAmin) is one of important experimental parameters for an event-related fMRl experiment designed with the stochastic stimulus. In this study, the most efficient SOAmin is explored for the stronger activation in motor and language tasks with the stimulus designed stochastically. MATERIALS AND METHODS: The event-related fMRl during motor and language tasks were obtained in four normal right-handed subjects. EPI-BOLD sequence is used at 1.5 Tesla MR system for the acquisition of event-related fMRl. For each task the subjects are responded for the stimulus' with 2, 3, 4, and 6 seconds SOAmin. The obtained images are processed with SPM99, and the p value is set as 0.05 for the significant activation detection. The Z value and the number of activated pixels are compared for each task. RESULTS: For the motor task, the primary and supplementary motor areas are activated, and for the language task the consistent activated signals are detected in the Broca's. The activated signal is to be stronger for the shorter SOAmin for both motor and language tasks. At primary motor area, the activated signals is the strongest for 3 seconds SOAmin and for the supplementary motor area the result with 2 seconds SOAmin shows the strongest activation. And the result of language task shows the strongest activation at the 2 seconds SOAmin. CONCLUSION: In the event-related fMRl of motor and language tasks with the stochastically designed stimulus, the 2 or 3 seconds SOAmin is efficient for more activated and clustered activation.

Multiphasic Perfusion CT in Acute Middle Cerebral Artery Ischemic Stroke: Prediction of Final Infarct Volume and Correlation with Clinical Outcome

OBJECTIVE: To assess the utility of multiphasic perfusion CT in the prediction of final infarct volume, and the relationship between lesion volume revealed by CT imaging and clinical outcome in acute ischemic stroke patients who have not undergone thrombolytic therapy. MATERIALS AND METHODS: Thirty-five patients underwent multiphasic perfusion CT within six hours of stroke onset. After baseline unenhanced helical CT scanning, contrast-enhanced CT scans were obtained 20, 34, 48, and 62 secs after the injection of 90 mL contrast medium at a rate of 3 mL/sec. CT peak and total perfusion maps were obtained from serial CT images, and the initial lesion volumes revealed by CT were compared with final infarct volumes and clinical scores. RESULTS: Overall, the lesion volumes seen on CT peak perfusion maps correlated most strongly with final infarct volumes (R2=0.819, p<0.001, slope of regression line=1.016), but individual data showed that they were less than final infarct volume in 31.4% of patients. In those who showed early clinical improvement (n=6), final infarct volume tended to be overestimated by CT peak perfusion mapping and only on total perfusion maps was there significant correlation between lesion volume and final infarct volume (R2=0.854, p=0.008). The lesion volumes depicted by CT maps showed moderate correlation with baseline clinical scores and clinical outcomes (R=0.445-0.706, p<=0.007). CONCLUSION: CT peak perfusion maps demonstrate strong correlation between lesion volume and final infarct volume, and accurately predict final infarct volume in about two-thirds of the 35 patients. The lesion volume seen on CT maps shows moderate correlation with clinical outcome.

Perfusion MR Imaging: Clinical Utility for the Differential Diagnosis of Various Brain Tumors

OBJECTIVE: To determine the utility of perfusion MR imaging in the differential diagnosis of brain tumors. MATERIALS AND METHODS: Fifty-seven patients with pathologically proven brain tumors (21 high-grade gliomas, 8 low-grade gliomas, 8 lymphomas, 6 hemangioblastomas, 7 metastases, and 7 various other tumors) were included in this study. Relative cerebral blood volume (rCBV) and time-to-peak (TTP) ratios were quantitatively analyzed and the rCBV grade of each tumor was also visually assessed on an rCBV map. RESULTS: The highest rCBV ratios were seen in hemangioblastomas, followed by high-grade gliomas, metastases, low-grade gliomas, and lymphomas. There was no significant difference in TTP ratios between each tumor group (p<0.05). At visual assessment, rCBV was high in 17 (81%) of 21 high-grade gliomas and in 4 (50%) of 8 low-grade gliomas. Hemangioblastomas showed the highest rCBV and lymphomas the lowest. CONCLUSION: Perfusion MR imaging may be helpful in the differentiation of thevarious solid tumors found in the brain, and in assessing the grade of the various glial tumors occurring there.

Language Lateralization by Functional MRI: A Comparison with Wada Test-preliminary Results

PURPOSE: To evaluate the usefulness of functional MR imaging (fMRI) for the determination of languagedomi-nance and to assess differences in language lateralization according to activation task or activated area. MATERIALS AND METHODS: Functional maps of the language area were obtained during word generation tasks (noun andverb) and a reading task in ten patients (9 right handed, 1 left handed) who had undergone the Wada test. MRexaminations were performed using a 1.5T scanner and the EPI BOLD technique. The SPM program was employed for thepostprocessing of images and the threshold for significance was set at p<0.001 or p<0.01. A lateralization indexwas calculated from the number of activated pixels in three hemispheric re-gions (whole hemisphere, frontal lobe,and temporoparietal lobe), and the results were compared with those of Wada tests. The results for lateralizationof language area were compared among stimulation tasks and regions and used for calculation of lateralizationindices. RESULTS: During the Wada test, nine patients were left dominant and one patient was right dominant forlan-guage. Language dominance based on activated signals in each hemisphere was consistent with the results of theWada test in 87.5% (verb and noun generation tasks) and 90% (reading task) of patients. Language domi-nancedetermined by activated signals in the frontal lobe was consistent in 87.5%, 75%, and 80% of patients in eachstimulation task (verb generation, noun generation, and reading), respectively. The consistency rate of ac-tivatedsignals in the temporoparietal lobe was 87.5%, 87.5% and 80% of patients in each task. The mean val-ue of thelateralization index, calculated on the basis of activated signals in the temporoparietal lobe was higher thanthat in the hemisphere or frontal lobe. The verb generation task showed a higher lateralization index than thenoun generation or reading task. CONCLUSION: The lateralization index was higher in the verb generation task andin the region of the tem-poroparietal lobe than in other stimulation tasks or regions. fMRI is a potentiallyuseful non-invasive method for the determination of language dominance.

functional MRI of Language Area

PURPOSE: To evaluate the usefulness of functional MR imaging(fMRI) for language mapping and determination of language lateralization. MATERIALS AND METHODS: Functional maps of the language area were obtained during word generation tasks and decision task in ten volunteers(7 right handed, 3 left-handed). MR examination were performed at 1.5T scanner with EPI BOLD technique. Each task consisted of three resting periods and two activation periods with each period of 30 seconds. Total acquisition time was 162sec. SPM program was used for the postprocessing of images. Statistical comparisons were performed by using t-statistics on a pixel-by-pixel basis after global normalization by ANCOVA. Activation areas were topographically analyzed(p<0.001) and activated pixels in each hemisphere were compared quantitatively by lateralization index. RESULTS: Significant activation signals were demonstrated in 9 of 10 volunteers. Activation signals were found in the premotor and motor cortices, the inferior frontal, inferior parietal, and mid-temporal lobes during stimulation tasks. In the right handed seven volunteers, activation of language areas was lateralized to the left side. Verb generation task produced stronger activation in the language areas and higher value of lateralization index than noun generation task or decision task. CONCLUSION: fMRI could be a useful non-invasive method for language mapping and determination of language dominance.

Analysis of fMRI Signal Using Independent Component Analysis

The fMRI signals are composed of many various signals. It is very difficult to find the accurate parameter for the model of fMRI signal containing only neural activity, though we may estimating the signal patterns by the modeling of several signal components. Besides the nose by the physiologic motion, the motion of object and noise of MR instruments make it more difficult to analyze signals of fMRI. Therefore, it is not easy to select an accurate reference data that can accurately reflect neural activity, and the method of an analysis of various signal patterns containing the information of neural activity is an issue of the post-processing methods for fMRI. In the present study, fMRI data was analyzed with the Independent Component Analysis(ICA) method that doesn't need a priori-knowledge or reference data. ICA can be more effective over the analytic method using cross-correlation analysis and can separate the signal patterns of the signals with delayed response or motion related components. The Principal Component Analysis (PCA) threshold, wavelet spatial filtering and analysis of a part of whole images can be used for the reduction of the freedom of data before ICA analysis, and these preceding analyses may be useful for a more effective analysis. As a result, ICA method will be effective for the analysis of signal patterns in fMRI and the pre-filtering may be necessary for the reduction of the degree of freedom of the data.

A Functional MR Imaging Study of Reading

PURPOSE: To evaluate the language areas activated by fMRI during different reading tasks and to assess the difference of activated areas according to each reading task MATERIALS AND METHODS: Functional maps of the language area were obtained during three reading tasks(Korean consonant letter, pseudoword, and word) in nine right-handed volunteers(7 males, 2 females). MR examinations were performed at 1.5T scanner with EPI BOLD technique(gradient echo shot EPI, TR/TE 3000/60, flip angle 90, matrix64 64, 5mm thickness, no slice gap). Each task consisted of three resting periods and two activation periods and each period lasted 30 seconds. We used SPM program for the postprocessing of images and siginficance level was set at p<0.01. Activated areas were topographically analyzed in each stimulus. RESULTS: Significant activated signals were demonstrated in all volunteers. Activated signals were seen in the frontal, temporal, parietal and occipital lobes during reading tasks and they were lateralized to the left hemisphere except occipital lobe. Letter and pseudoword produced stronger activated signals than word, and the activated signals were more lateralized to the left hemisphere in pseudoword reading than in letter reading. CONCLUSION: Activated signals were induced in the language areas by reading task of letter or wordform. Greater activation of language areas was induced when letter or pseuowords were presented than familiar words.