Figure 1.
Custom-made I-123-ioflupane template.
Transversal slice (left). ROIs for left/right caudate and putamen used for hottest voxel analysis, and ROI for the reference region used for intensity scaling, all defined in MNI space (middle). The union of caudate and putamen ROI was used as ROI for the whole striatum. Fusion image (right).
Figure 2.
Example page from the pdf document for visual scoring.
The pdf document comprised one page for each I-123-ioflupane SPECT image showing a 12 mm thick slab (a, left) and 4x4 slices of 4 mm thickness (a, right). Example I-123-ioflupane SPECTs used as reference images for the visual scoring (b).
Table 1.
Results of the semi-quantitative analysis of the phantom studies.
Table 2.
Results of the semi-quantitative analysis of the patient studies.
Figure 3.
Bland-Altman plots comparing the SBR of the caudate (a) and the putamen (b) between CT-based and Chang AC (SBRs of both hemispheres were included independently, i.e. n = 124).
Different scales were chosen for abscissae and ordinates in a and b for display purposes. The horizontal continuous line represents the mean difference, the dashed lines indicate the 95% confidence interval. The given p-value corresponds to the one-sample t-test for zero mean.
Figure 4.
ROC curves for the differentiation between reduced and normal DAT availability by the SBR of the caudate (a) and the putamen (b) (minimum over both hemispheres).
Table 3.
Cohen’s unweighted κ (mean ±1 standard deviation) for inter-rater agreement of visual scoring of DAT availability.
Figure 5.
SPECT underestimates the true activity concentration in small structures such as the striatum and its substructures due to the limited spatial resolution in the reconstructed SPECT image (partial volume effect, PVE).
In order to estimate the extent of underestimation in the present study, the reconstructed spatial resolution was estimated on the basis of a line source measurement using the same acquisition and reconstruction protocol as in the measurements of the striatal phantom and the patients included in the present study (no AC). Spatial resolution was found to be about 8 mm full-width-at-half-maximum (FWHM). Then a high-resolution CT of the striatal phantom was segmented manually (top row; from left to right: transversal, sagittal and coronal slice). Voxel values in the striatum were set to 6.5, voxel values in the background to 1.0 in order to simulate the actual SBR of about 5.5 in the phantom studies (Table 1). Then the segmented CT image was smoothed with a 3-dimensional Gaussian kernel with 8 mm FWHM to simulate the PVE in SPECT (bottom row). ROI analysis of the smoothed image resulted in a striatal SBR of 3.2 which underestimates the actual SBR of 5.5 by about 42%.
Figure 6.
Slab of 12 mm thickness of the scaled, stereotactically normalized I-123-ioflupane SPECT averaged over all patients with normal DAT availability (top). Slab displaying the coefficient of variation (%) of the DVR over all patients with normal DAT availability (bottom).