Comparison of Reconstruction Algorithms for F-18 FP CIT PET Images

Fludeoxyglucose-18-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane positron emission tomography (F-18 FP CIT PET) was used for the diagnosis of Parkinson’s disease in nuclear medicine. However, no study of the effect of reconstruction parameters on the quality images obtained using F-18 FP CIT PET has been done. For that reason, this study compares the quality of F-18 FP CIT PET images reconstructed with different algorithms in terms of the recovery coefficient (RC), maximum PET counts, and binding potential (BP). The RCs of images were measured according to the National Electrical Manufacturers Association (NEMA) standard NU 4-2008 (NEMA NU4-2008). The PET images of the phantoms were reconstructed using various reconstruction algorithms (OSEM2D, FBP, 3DRP and OSEM3D/MAP) and filters. For the FBP reconstruction, the ramp, Butterworth (order: 1), Hamming, Hanning, Parzen, and SheppLogan filters were used. The cutoff frequency was 0.5 (even though the, ramp filter needed no cut-off frequency). For the OSEM3D/MAP reconstruction, various smoothing factors (β = 0.05, 0.5 and 1.5) were used with 18 iterations number. The β value was provided as a penalty function for constraint on neighboring voxels during the MAP algorithm. The β values of 0.05, 0.5 and 1.5 corresponded to predicted target resolutions of 1.5 mm, 2 mm, and 2.3 mm for the OSEM3D/MAP reconstruction algorithm, respectively. For the 3DRP reconstruction, Hanning filters were used. We used OSEM2D with 4 iterations and 16 subsets (default number in Siemens Inveon PET scanner) in this study for OSEM2D method. To compare the chosen parameters between the F-18 FP CIT PET images and phantoms, we used BALB nude mice (20 g body weight) were used to obtain mouse images. For evaluating the reconstruction methods, the maximum PET counts (counts/s/voxel) and BP (for image contrast ratio with striatum and cerebellum) of each reconstruction algorithm the striatal diameter of mice was observed to be 3 mm. Therefore, the RC values of the phantoms with a diameter of 3 mm were chosen. For phantoms with Φ = 3 mm, the OSEM2D provided the most appropriate 0.95 of RC value. Moreover, the maximum PET counts and the BP of the striatum with the OSEM2D reconstruction were observed to be high compared to the value for the other reconstruction methods. OSEM3D/MAP also showed high values for the maximum PET counts and the BP; however, the RC of OSEM3D/MAP (β = 0.05) exceeded 1 at Φ = 3 mm, and other OSEM3D/MAPs (β = 1.5 and 0.5) were lower than those of OSEM2D. Therefore, OSEM3D/MAP was not considered for decisions regarding the optimal reconstruction method. Through actual PET images we verified that the images with OSEM2D were identified more clearly and with higher image contrast. The OSEM2D reconstruction algorithm provided the best values (0.95) on reconstructed PET data; thus, OSE2D would be suitable for quantification of F-18 FP CIT PET images of mice obtained with a Siemens Inveon PET.