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Functional Co-integration of PET and ERP LORETA image during Working Memory Tasks
Neurolmage
13, Number
6, 2001,
Part 2 of 2 Parts 1 D E C;[@
METHODS
- ANALYSIS
Functional Co-integration of PET and ERP LORETA during Working Memory Tasks
image
Hae-Jeong Park*, Bo Reom Lee?, Sang-Soo ChoS, Jae-Jin Kim+, Myung-Sun Kim+, Jun Soo Kwon$ *Institute of Biomedical Engineering TDept. of Biomedical Engineering $Dept. of Psychiatry, Seoul National University, College of Medicine, KOREA INTRODUCTION PET and ERP are different modalities to show functional brain activities. PET image gives no precise temporal information of brain activity. Therefore, integrating PET with the high time resolution ERP is expected to provide more information on the cognitive study. LORETA (Low Resolution Electromagnetic Tomography) makes it possible to reconstruct the 3-D brain electrical activity. Previous ERP and PET co-registration were mainly restricted to the several equivalent dipole sources and not three-dimensional current densities. In this study, we integrated current density maps derived from 12%channel ERP and PET images of each subject during working memory task with the reference of his/her MRI. By this technique, we could investigate the brain substrate of working memory with time. MATERIALS
AND
METHODS
Five healthy right-handed Koreans were studied. The experimental tasks were several variants of a sequential object task with 2-back condition where stimuli consisted of visually presented simple pictures and Korean words. Subjects were instructed to keep in mind both the identity and order of the two previous objects and to continuously update the mental record with each subsequently presented stimulus. The control task was to pay focused attention to only a circle on a list of simple pictures. Three-dimensional Tl -weighted MR images were acquired on a 1.5-T GE SIGNA Scanner with a voxel size of 0.94 x 0.94 x 1.5 mm. 123 channel ERP data were recorded with the Neuroscan 4.0. [‘SO]H20 PET (Siemens-CTI, USA) images were measured with a 128 x 128 x 47 matrix, with a voxel size of 2.1 x2.1x3.4 mm. From the preprocessed 123-channel ERP data of each subject, we performed the LORETA using CURRY 4.0. MR images of each subject were used for establishing a realistic head model and for BEM. Current densities at 37158 previously assigned grid points based on Talairach coordinates were estimated during the tasks between 300 ms and 900 ms with the interval of 10 ms. Smoothed experimental images were subtracted by control PET images and were coregistered into MRI using SPM99 using template-based affine transformation. Because both PET and ERP were coregistered to a referenced MRI, ERP could be superimposed to PET-MRI registered images without any transformation on MATLAB. The time courses of ERP activities are displayed on PET-MRI images. RESULTS The results of LORETA were similar to those of PET study. PET study shows significant activations on the right prefrontal area. In the ERP current density map, the right prefrontal activation is detected concurrently with the PET result. Also, activations on left parietal areas during 300 to 500 ms and occipital activations after 800 ms are detected. We found the possibility of investigating temporal processes of brain activity by integrating current density maps of ERP into PET. Further application to more cases will be required to validate the usefulness of our co-registration techniques.
S216
13, Number
6, 2001,
Part 2 of 2 Parts 1 D E C;[@
METHODS
- ANALYSIS
Functional Co-integration of PET and ERP LORETA during Working Memory Tasks
image
Hae-Jeong Park*, Bo Reom Lee?, Sang-Soo ChoS, Jae-Jin Kim+, Myung-Sun Kim+, Jun Soo Kwon$ *Institute of Biomedical Engineering TDept. of Biomedical Engineering $Dept. of Psychiatry, Seoul National University, College of Medicine, KOREA INTRODUCTION PET and ERP are different modalities to show functional brain activities. PET image gives no precise temporal information of brain activity. Therefore, integrating PET with the high time resolution ERP is expected to provide more information on the cognitive study. LORETA (Low Resolution Electromagnetic Tomography) makes it possible to reconstruct the 3-D brain electrical activity. Previous ERP and PET co-registration were mainly restricted to the several equivalent dipole sources and not three-dimensional current densities. In this study, we integrated current density maps derived from 12%channel ERP and PET images of each subject during working memory task with the reference of his/her MRI. By this technique, we could investigate the brain substrate of working memory with time. MATERIALS
AND
METHODS
Five healthy right-handed Koreans were studied. The experimental tasks were several variants of a sequential object task with 2-back condition where stimuli consisted of visually presented simple pictures and Korean words. Subjects were instructed to keep in mind both the identity and order of the two previous objects and to continuously update the mental record with each subsequently presented stimulus. The control task was to pay focused attention to only a circle on a list of simple pictures. Three-dimensional Tl -weighted MR images were acquired on a 1.5-T GE SIGNA Scanner with a voxel size of 0.94 x 0.94 x 1.5 mm. 123 channel ERP data were recorded with the Neuroscan 4.0. [‘SO]H20 PET (Siemens-CTI, USA) images were measured with a 128 x 128 x 47 matrix, with a voxel size of 2.1 x2.1x3.4 mm. From the preprocessed 123-channel ERP data of each subject, we performed the LORETA using CURRY 4.0. MR images of each subject were used for establishing a realistic head model and for BEM. Current densities at 37158 previously assigned grid points based on Talairach coordinates were estimated during the tasks between 300 ms and 900 ms with the interval of 10 ms. Smoothed experimental images were subtracted by control PET images and were coregistered into MRI using SPM99 using template-based affine transformation. Because both PET and ERP were coregistered to a referenced MRI, ERP could be superimposed to PET-MRI registered images without any transformation on MATLAB. The time courses of ERP activities are displayed on PET-MRI images. RESULTS The results of LORETA were similar to those of PET study. PET study shows significant activations on the right prefrontal area. In the ERP current density map, the right prefrontal activation is detected concurrently with the PET result. Also, activations on left parietal areas during 300 to 500 ms and occipital activations after 800 ms are detected. We found the possibility of investigating temporal processes of brain activity by integrating current density maps of ERP into PET. Further application to more cases will be required to validate the usefulness of our co-registration techniques.
S216