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Feasibility of Computed Tomography-Guided Methods for Spatial Normalization of Dopamine Transporter Positron Emission Tomography Image.

Kim JS, Cho H, Choi JY, Lee SH, Ryu YH, Lyoo CH, Lee MS - PLoS ONE (2015)

Bottom Line: The CT images were modified in two ways, skull-stripping (ssCT) and intensity transformation (itCT).The SUVR values measured with FreeSurfer-generated VOIs (FSVOI) overlaid on original PET images were also used as a gold standard for comparison.Putaminal SUVR values were highly effective for discriminating PD patients from controls.

View Article: PubMed Central - PubMed

Affiliation: Molecular Imaging Research Center, Korea Institute Radiological and Medical Sciences, Seoul, South Korea.

ABSTRACT

Background: Spatial normalization is a prerequisite step for analyzing positron emission tomography (PET) images both by using volume-of-interest (VOI) template and voxel-based analysis. Magnetic resonance (MR) or ligand-specific PET templates are currently used for spatial normalization of PET images. We used computed tomography (CT) images acquired with PET/CT scanner for the spatial normalization for [18F]-N-3-fluoropropyl-2-betacarboxymethoxy-3-beta-(4-iodophenyl) nortropane (FP-CIT) PET images and compared target-to-cerebellar standardized uptake value ratio (SUVR) values with those obtained from MR- or PET-guided spatial normalization method in healthy controls and patients with Parkinson's disease (PD).

Methods: We included 71 healthy controls and 56 patients with PD who underwent [18F]-FP-CIT PET scans with a PET/CT scanner and T1-weighted MR scans. Spatial normalization of MR images was done with a conventional spatial normalization tool (cvMR) and with DARTEL toolbox (dtMR) in statistical parametric mapping software. The CT images were modified in two ways, skull-stripping (ssCT) and intensity transformation (itCT). We normalized PET images with cvMR-, dtMR-, ssCT-, itCT-, and PET-guided methods by using specific templates for each modality and measured striatal SUVR with a VOI template. The SUVR values measured with FreeSurfer-generated VOIs (FSVOI) overlaid on original PET images were also used as a gold standard for comparison.

Results: The SUVR values derived from all four structure-guided spatial normalization methods were highly correlated with those measured with FSVOI (P < 0.0001). Putaminal SUVR values were highly effective for discriminating PD patients from controls. However, the PET-guided method excessively overestimated striatal SUVR values in the PD patients by more than 30% in caudate and putamen, and thereby spoiled the linearity between the striatal SUVR values in all subjects and showed lower disease discrimination ability. Two CT-guided methods showed comparable capability with the MR-guided methods in separating PD patients from controls and showed better correlation between putaminal SUVR values and the parkinsonian motor severity than the PET-guided method.

Conclusion: CT-guided spatial normalization methods provided reliable striatal SUVR values comparable to those obtained with MR-guided methods. CT-guided methods can be useful for analyzing dopamine transporter PET images when MR images are unavailable.

No MeSH data available.


Related in: MedlinePlus

Mean and standard deviation (SD) images of each spatial normalization method and the results of voxel-based comparison between the healthy controls (HC) and Parkinson’s disease (PD) patients.For PD patients images were flipped to locate more affected side (contralateral to the clinically worse side; W) on the left (L) and the less affected side (contralateral to the clinically better side; B) on the right (R). The mean images of controls and PD patients derived from four structure-guided spatial normalization methods are similar. However, the caudate and anterior part of the putamen of PD patients were overestimated, and thereby, the mean image of PD patients derived from the PET-guided method shows higher uptake and in those regions. In contrast to the tendency shown in the mean images, the SD images of two CT-guided methods show higher SD values around the striatum, suggesting higher spatial variability. Voxel-based comparison between the controls and PD patients (family-wise error corrected) show the highest significance with the dtMR-guided method, and two CT-guided methods were inferior to the MR-guided methods. Color bars for mean and SD images represent standardized uptake value ratio (SUVR), and that for the voxel-based comparison images represents T-value for the comparison. Abbreviations: cvMR = MR-guided spatial normalization with conventional normalization tool, dtMR = MR-guided spatial normalization with DARTEL toolbox, ssCT = skull-stripped CT-guided spatial normalization, itCT = intensity transformed CT-guided spatial normalization, PET = PET-guided spatial normalization.
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pone.0132585.g006: Mean and standard deviation (SD) images of each spatial normalization method and the results of voxel-based comparison between the healthy controls (HC) and Parkinson’s disease (PD) patients.For PD patients images were flipped to locate more affected side (contralateral to the clinically worse side; W) on the left (L) and the less affected side (contralateral to the clinically better side; B) on the right (R). The mean images of controls and PD patients derived from four structure-guided spatial normalization methods are similar. However, the caudate and anterior part of the putamen of PD patients were overestimated, and thereby, the mean image of PD patients derived from the PET-guided method shows higher uptake and in those regions. In contrast to the tendency shown in the mean images, the SD images of two CT-guided methods show higher SD values around the striatum, suggesting higher spatial variability. Voxel-based comparison between the controls and PD patients (family-wise error corrected) show the highest significance with the dtMR-guided method, and two CT-guided methods were inferior to the MR-guided methods. Color bars for mean and SD images represent standardized uptake value ratio (SUVR), and that for the voxel-based comparison images represents T-value for the comparison. Abbreviations: cvMR = MR-guided spatial normalization with conventional normalization tool, dtMR = MR-guided spatial normalization with DARTEL toolbox, ssCT = skull-stripped CT-guided spatial normalization, itCT = intensity transformed CT-guided spatial normalization, PET = PET-guided spatial normalization.

Mentions: Mean SUVR images of the control subjects were similar across different spatial normalization methods. However, the mean SUVR image of the PET-guided method showed erroneous overestimation of the caudate and anterior putaminal uptake and lower contrast of asymmetry of putaminal uptake. Standard deviation (SD) images of dtMR- and PET-guided method in control subjects showed very low and rather homogeneous SD values in the entire striatum, whereas the SD images of the cvMR-guided and the two CT-guided methods showed higher SD values around the striatal border, suggesting greater spatial variability. As expected, the voxel-based comparison between the controls and PD patients showed the greatest differences in dtMR- and cvMR-guided methods (family-wise error corrected P < 0.001). Two CT-guided methods also showed highly significant differences across the entire putamen. Nevertheless, the level of significance for the anterior putamen was lowest for the PET-guided method (Fig 6).


Feasibility of Computed Tomography-Guided Methods for Spatial Normalization of Dopamine Transporter Positron Emission Tomography Image.

Kim JS, Cho H, Choi JY, Lee SH, Ryu YH, Lyoo CH, Lee MS - PLoS ONE (2015)

Mean and standard deviation (SD) images of each spatial normalization method and the results of voxel-based comparison between the healthy controls (HC) and Parkinson’s disease (PD) patients.For PD patients images were flipped to locate more affected side (contralateral to the clinically worse side; W) on the left (L) and the less affected side (contralateral to the clinically better side; B) on the right (R). The mean images of controls and PD patients derived from four structure-guided spatial normalization methods are similar. However, the caudate and anterior part of the putamen of PD patients were overestimated, and thereby, the mean image of PD patients derived from the PET-guided method shows higher uptake and in those regions. In contrast to the tendency shown in the mean images, the SD images of two CT-guided methods show higher SD values around the striatum, suggesting higher spatial variability. Voxel-based comparison between the controls and PD patients (family-wise error corrected) show the highest significance with the dtMR-guided method, and two CT-guided methods were inferior to the MR-guided methods. Color bars for mean and SD images represent standardized uptake value ratio (SUVR), and that for the voxel-based comparison images represents T-value for the comparison. Abbreviations: cvMR = MR-guided spatial normalization with conventional normalization tool, dtMR = MR-guided spatial normalization with DARTEL toolbox, ssCT = skull-stripped CT-guided spatial normalization, itCT = intensity transformed CT-guided spatial normalization, PET = PET-guided spatial normalization.
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pone.0132585.g006: Mean and standard deviation (SD) images of each spatial normalization method and the results of voxel-based comparison between the healthy controls (HC) and Parkinson’s disease (PD) patients.For PD patients images were flipped to locate more affected side (contralateral to the clinically worse side; W) on the left (L) and the less affected side (contralateral to the clinically better side; B) on the right (R). The mean images of controls and PD patients derived from four structure-guided spatial normalization methods are similar. However, the caudate and anterior part of the putamen of PD patients were overestimated, and thereby, the mean image of PD patients derived from the PET-guided method shows higher uptake and in those regions. In contrast to the tendency shown in the mean images, the SD images of two CT-guided methods show higher SD values around the striatum, suggesting higher spatial variability. Voxel-based comparison between the controls and PD patients (family-wise error corrected) show the highest significance with the dtMR-guided method, and two CT-guided methods were inferior to the MR-guided methods. Color bars for mean and SD images represent standardized uptake value ratio (SUVR), and that for the voxel-based comparison images represents T-value for the comparison. Abbreviations: cvMR = MR-guided spatial normalization with conventional normalization tool, dtMR = MR-guided spatial normalization with DARTEL toolbox, ssCT = skull-stripped CT-guided spatial normalization, itCT = intensity transformed CT-guided spatial normalization, PET = PET-guided spatial normalization.
Mentions: Mean SUVR images of the control subjects were similar across different spatial normalization methods. However, the mean SUVR image of the PET-guided method showed erroneous overestimation of the caudate and anterior putaminal uptake and lower contrast of asymmetry of putaminal uptake. Standard deviation (SD) images of dtMR- and PET-guided method in control subjects showed very low and rather homogeneous SD values in the entire striatum, whereas the SD images of the cvMR-guided and the two CT-guided methods showed higher SD values around the striatal border, suggesting greater spatial variability. As expected, the voxel-based comparison between the controls and PD patients showed the greatest differences in dtMR- and cvMR-guided methods (family-wise error corrected P < 0.001). Two CT-guided methods also showed highly significant differences across the entire putamen. Nevertheless, the level of significance for the anterior putamen was lowest for the PET-guided method (Fig 6).

Bottom Line: The CT images were modified in two ways, skull-stripping (ssCT) and intensity transformation (itCT).The SUVR values measured with FreeSurfer-generated VOIs (FSVOI) overlaid on original PET images were also used as a gold standard for comparison.Putaminal SUVR values were highly effective for discriminating PD patients from controls.

View Article: PubMed Central - PubMed

Affiliation: Molecular Imaging Research Center, Korea Institute Radiological and Medical Sciences, Seoul, South Korea.

ABSTRACT

Background: Spatial normalization is a prerequisite step for analyzing positron emission tomography (PET) images both by using volume-of-interest (VOI) template and voxel-based analysis. Magnetic resonance (MR) or ligand-specific PET templates are currently used for spatial normalization of PET images. We used computed tomography (CT) images acquired with PET/CT scanner for the spatial normalization for [18F]-N-3-fluoropropyl-2-betacarboxymethoxy-3-beta-(4-iodophenyl) nortropane (FP-CIT) PET images and compared target-to-cerebellar standardized uptake value ratio (SUVR) values with those obtained from MR- or PET-guided spatial normalization method in healthy controls and patients with Parkinson's disease (PD).

Methods: We included 71 healthy controls and 56 patients with PD who underwent [18F]-FP-CIT PET scans with a PET/CT scanner and T1-weighted MR scans. Spatial normalization of MR images was done with a conventional spatial normalization tool (cvMR) and with DARTEL toolbox (dtMR) in statistical parametric mapping software. The CT images were modified in two ways, skull-stripping (ssCT) and intensity transformation (itCT). We normalized PET images with cvMR-, dtMR-, ssCT-, itCT-, and PET-guided methods by using specific templates for each modality and measured striatal SUVR with a VOI template. The SUVR values measured with FreeSurfer-generated VOIs (FSVOI) overlaid on original PET images were also used as a gold standard for comparison.

Results: The SUVR values derived from all four structure-guided spatial normalization methods were highly correlated with those measured with FSVOI (P < 0.0001). Putaminal SUVR values were highly effective for discriminating PD patients from controls. However, the PET-guided method excessively overestimated striatal SUVR values in the PD patients by more than 30% in caudate and putamen, and thereby spoiled the linearity between the striatal SUVR values in all subjects and showed lower disease discrimination ability. Two CT-guided methods showed comparable capability with the MR-guided methods in separating PD patients from controls and showed better correlation between putaminal SUVR values and the parkinsonian motor severity than the PET-guided method.

Conclusion: CT-guided spatial normalization methods provided reliable striatal SUVR values comparable to those obtained with MR-guided methods. CT-guided methods can be useful for analyzing dopamine transporter PET images when MR images are unavailable.

No MeSH data available.


Related in: MedlinePlus