Abstract
3130
Objectives: The specific binding ratio (SBR) is used to evaluate the degree of tracer binding to the striatum in dopamine transporter SPECT. However, the SBR is underestimated because of the partial volume effect (PVE). The present study aimed to evaluate the accuracy of the SBR calculated for the caudate and putamen with the minimum PVE by our method. A second aim was to determine the number of iterations for calculating the SBR by our method.
Methods: The right caudate, right putamen, left caudate, left putamen, and background of a striatal phantom were filled with 50.35, 50.35, 29.49, 23.46, and 5.19 [kBq/mL] of 123I solution, respectively. The SPECT image was reconstructed by 3D OSEM. In addition, scatter and attenuation corrections were performed. By using PMOD software (PMOD Technologies), the volumes of interest (VOIs) for the caudate, putamen and background were established in CT image and applied to the SPECT image. Values of every quarter from 0 to 1 (0, 0.25, 0.5, 0.75, 1) were assigned to each VOI, and images blurred with the full width at half maximum (FWHM) of the SPECT device were generated. These images were defined as generated images; the image obtained by imaging was defined as a real image. The difference between a real and generated image was calculated. The values were again assigned to each VOI by a quarter within the range before and after the assigned values, which minimized the difference between the real and generated image. The images blurred with the FWHM were also generated. That is, if the difference between the real and generated image is minimum when 0.5 is assigned to the right caudate VOI, then, 0.25, 0.375, 0.5, 0.625, and 0.75 are assigned to the right caudate VOI. This process was iterated 8 times. Finally, the SBRs for the caudate and putamen were calculated using the values when the difference between the real and generated image was the smallest. The SBRs for the striatum were also calculated. The calculated SBRs were compared with the theoretical SBRs and the errors between them were calculated. In addition, SBRs for the striatum were compared with those calculated using our method and those calculated using DaTView software (AZE, Japan). The optimum number of iterations was also examined. When the difference of SBRs between the before and after iterations was less than 5%, the SBRs were considered as converged.
Results: As the calculation was iterated, the SBRs converged, and finally the errors between the calculated SBRs and the theoretical SBRs for the right striatum, right caudate, right putamen, left striatum, left caudate, and left putamen were 6.54, 6.54, 6.54, 18.0, 24.7, and 14.7%, respectively. The errors of the SBRs for the striatum calculated using our method were less than those calculated using DaTView. When the number of iterations was 6 or more, the errors of the SBRs before and after the iteration were less than 5%.
Conclusions: The errors between the calculated SBR and the theoretical SBR of the right striatum, right caudate, right putamen, left striatum, left caudate, and left putamen were 6.54, 6.54, 6.54, 18.0, 24.7, and 14.7%, respectively. The optimum number of iterations for calculating the SBR was 6 times.