Effect of normalization method on image uniformity and binding potential estimates on microPET

This study investigates different detector normalization procedures for a small animal scanner, specifically the Concorde microPET^® R4. The procedures were compared in terms of: (i) image uniformity, (ii) performance as a function of count rate, and (iii) impact on the estimate of the binding potential (BP) in brain rat studies. Image uniformity studies were performed on two cylindrical phantoms of different size filled with an aqueous concentration of ¹¹C (38 kBq/mL and 615 kBq/mL). BP was estimated with the Logan graphical approach on 12 ¹¹C-Methylphenidate and 9 ¹¹C-Dihydrotetrabenazine rat studies processed with all the normalization procedures. We found that: 1) the combination, the geometry normalized combination, the component-point, and the geometry normalized component procedures significantly improve radial image uniformity compared to the direct-point and direct-cylinder procedures, 2) the geometry normalized combination procedure seems to provide the best radial and axial uniformity, 3) a mismatch between the count rates at which the normalization and the emission scans are acquired degrades the axial uniformity by 47% to 98% whereas this effect was not observed for radial uniformity, and 4) the difference in BP values obtained from data corrected with different normalization procedures is as high as 15% for normal striatum and 75% for lesion striatum.