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Dopamine transporter binding corrected for tissue heterogeneity and partial volume effect using [11C]PE2I and PET
Poster Presentations / NeuroImage 31 (2006) T44 – T186
T87
Poster Presentation No.: 041
Dopamine transporter binding corrected for tissue heterogeneity and partial volume effect using [11C]PE2I and PET Ikuo Odano, A. Jucaite, H. Olsson, P. Karlsson, S. Pauli, C. Halldin, L. Farde Karolinska Institute, Sweden
Objectives: Accuracy in in vivo quantification of brain function with positron emission tomography (PET) has often been limited by the tissue heterogeneity (TH) and partial volume effect (PVE). We have presented quantitative analysis of dopamine transporter binding using [11C]PE2I and PET in normal human brain (Jucaite et al., 2006), in which we applied kinetic analysis and reference tissue models using cerebellum as a reference region. However, the tracer activity may be underestimated in the striatum mainly caused by TH and in the cerebellum caused by both TH and PVE. The purpose of the study is to propose a new modified algorithm of TH and PVE correction and to quantify receptor binding parameters in human brain. Methods: The brain structure consists of gray matter, white matter and extracerebral space, and the fraction of each component and tracer concentration is defined as PG, PW and PEXT, and CG, CW and CEXT, respectively. The tracer concentration of gray matter corrected for TH and/or PVE, CG(t), is described as follows: CG(t) = CROI(t) / PG a * PW/PG) * CsubW(t), where CROI(t) is the concentration of the ROI. CsubW(t) is the substitution of white matter of the ROI, which is obtained from other white matter. a is the transfer constant, which makes correlation between CW(t) and CsubW(t). [11C]PE2I and PET studies were performed on eight normal volunteers, and metabolitecorrected arterial plasma input function was obtained. After co-registering MRI and PET images and placing ROIs on the cerebellum, cerebellar white matter and peduncle, putamen and centrum semiovale, we performed segmentation procedures using SPM and calculated the segmentation fraction ratios. The data were analyzed using the two- and three-compartment models (2CPM and 3CPM), linear graphical analysis and simplified reference tissue model. The binding parameters were compared before and after correction. Results: Distribution volume of the cerebellum and putamen increased by approximately 10% after correction. Binding potential of the putamen increased by approximately 5% after correction. The total concentration for CG(t) increased after correction, and the fraction increased was mainly caused by the increase of specific binding not by the free ligand. The statistical significance for curve fitting with 2CPM and 3CPM did not change. Conclusion: The heterogeneity and partial volume correction using MRI segmentation model is useful to obtain reliable values of binding parameters for receptor mapping studies. Reference: Jucaite, A., et al., 2006(Mar 3). Eur. J. Nuclear Med. Mol. Imaging; Epub ahead of print. doi:10.1016/j.neuroimage.2006.04.075
T87
Poster Presentation No.: 041
Dopamine transporter binding corrected for tissue heterogeneity and partial volume effect using [11C]PE2I and PET Ikuo Odano, A. Jucaite, H. Olsson, P. Karlsson, S. Pauli, C. Halldin, L. Farde Karolinska Institute, Sweden
Objectives: Accuracy in in vivo quantification of brain function with positron emission tomography (PET) has often been limited by the tissue heterogeneity (TH) and partial volume effect (PVE). We have presented quantitative analysis of dopamine transporter binding using [11C]PE2I and PET in normal human brain (Jucaite et al., 2006), in which we applied kinetic analysis and reference tissue models using cerebellum as a reference region. However, the tracer activity may be underestimated in the striatum mainly caused by TH and in the cerebellum caused by both TH and PVE. The purpose of the study is to propose a new modified algorithm of TH and PVE correction and to quantify receptor binding parameters in human brain. Methods: The brain structure consists of gray matter, white matter and extracerebral space, and the fraction of each component and tracer concentration is defined as PG, PW and PEXT, and CG, CW and CEXT, respectively. The tracer concentration of gray matter corrected for TH and/or PVE, CG(t), is described as follows: CG(t) = CROI(t) / PG a * PW/PG) * CsubW(t), where CROI(t) is the concentration of the ROI. CsubW(t) is the substitution of white matter of the ROI, which is obtained from other white matter. a is the transfer constant, which makes correlation between CW(t) and CsubW(t). [11C]PE2I and PET studies were performed on eight normal volunteers, and metabolitecorrected arterial plasma input function was obtained. After co-registering MRI and PET images and placing ROIs on the cerebellum, cerebellar white matter and peduncle, putamen and centrum semiovale, we performed segmentation procedures using SPM and calculated the segmentation fraction ratios. The data were analyzed using the two- and three-compartment models (2CPM and 3CPM), linear graphical analysis and simplified reference tissue model. The binding parameters were compared before and after correction. Results: Distribution volume of the cerebellum and putamen increased by approximately 10% after correction. Binding potential of the putamen increased by approximately 5% after correction. The total concentration for CG(t) increased after correction, and the fraction increased was mainly caused by the increase of specific binding not by the free ligand. The statistical significance for curve fitting with 2CPM and 3CPM did not change. Conclusion: The heterogeneity and partial volume correction using MRI segmentation model is useful to obtain reliable values of binding parameters for receptor mapping studies. Reference: Jucaite, A., et al., 2006(Mar 3). Eur. J. Nuclear Med. Mol. Imaging; Epub ahead of print. doi:10.1016/j.neuroimage.2006.04.075