Clinical 123 I-2-b-carbomethoxy-3b-(4-iodophenyl)-N-(3-fluoropropyl)nortropane ( 123 I-FP-CIT) SPECT studies are commonly performed and reported using visual evaluation of tracer binding, an inherently subjective method. Increased objectivity can potentially be obtained using semiquantitative analysis. In this study, we assessed whether semiquantitative analysis of 123 I-FP-CIT tracer binding created more reproducible clinical reporting. A secondary aim was to determine in what form semiquantitative data should be provided to the reporter. Methods: Fifty-four patients referred for the assessment of nigrostriatal dopaminergic degeneration were scanned using SPECT/CT, followed by semiquantitative analysis calculating striatal binding ratios (SBRs) and caudate-to-putamen ratios (CPRs). Normal reference values were obtained using 131 healthy controls enrolled on a multicenter initiative backed by the European Association of Nuclear Medicine. A purely quantitative evaluation was first performed, with each striatum scored as normal or abnormal according to reference values. Three experienced nuclear medicine physicians then scored each striatum as normal or abnormal, also indicating cases perceived as difficult, using visual evaluation, visual evaluation in combination with SBR data, and visual evaluation in combination with SBR and CPR data. Intra-and interobserver agreement and agreement between observers and the purely quantitative evaluation were assessed using k-statistics. The agreement between scan interpretation and clinical diagnosis was assessed for patients with a postscan clinical diagnosis available (n 5 35). Results: The physicians showed consistent reporting, with a good intraobserver agreement obtained for the visual interpretation (mean k 6 SD, 0.95 6 0.029). Although visual interpretation of tracer binding gave good interobserver agreement (0.80 6 0.045), this was improved as SBRs (0.86 6 0.070) and CPRs (0.95 6 0.040) were provided. The number of striata perceived as difficult to interpret decreased as semiquantitative data were provided (30 for the visual interpretation; 0 as SBR and CPR values were given). The agreement between physicians' interpretations and the purely quantitative evaluation showed that readers used the semiquantitative data to different extents, with a more experienced reader relying less on the semiquantitative data. Good agreement between scan interpretation and clinical diagnosis was seen. Conclusion: A combined approach of visual assessment and semiquantitative analysis of tracer binding created more reproducible clinical reporting of 123 I-FP-CIT SPECT studies. Physicians should have access to both SBR and CPR data to minimize interobserver variability.

This study aimed to investigate image quality for a comprehensive set of isotopes ( 18 F, 11 C, 89 Zr, 124 I, 68 Ga, and 90 Y) on 2 clinical scanners: a PET/CT scanner and a PET/MR scanner. Methods: Image quality and spatial resolution were tested according to NU 2-2007 of the National Electrical Manufacturers Association. An imagequality phantom was used to measure contrast recovery, residual bias in a cold area, and background variability. Reconstruction methods available on the 2 scanners were compared, including point-spreadfunction correction for both scanners and time of flight for the PET/ CT scanner. Spatial resolution was measured using point sources and filtered backprojection reconstruction. Results: With the exception of 90 Y, small differences were seen in the hot-sphere contrast recovery of the different isotopes. Cold-sphere contrast recovery was similar across isotopes for all reconstructions, with an improvement seen with time of flight on the PET/CT scanner. The lower-statistic 90 Y scans yielded substantially lower contrast recovery than the other isotopes. When isotopes were compared, there was no difference in measured spatial resolution except for PET/MR axial spatial resolution, which was significantly higher for 124 I and 68 Ga. Conclusion: Overall, both scanners produced good images with 18 F, 11 C, 89 Thefir st isotopes used in PET were those of elements common in the human body, such as 15 O, 13 N, and 11 C. They found applications in both research and clinical PET: 15 O measured brain blood flow (1); 13 N assessed myocardial perfusion (2); and 11 C was successful in several applications, such as brain tumor imaging (3), prostate cancer staging (4), and cardiology (5). The short half-lives of these isotopes require an on-site cyclotron, a limiting factor for their widespread use.PET grew rapidly from the late 1990s. Approval for reimbursement by the Centers for Medicare and Medicaid Services, the longer half-life of 18 F, and the simple uptake mechanism of 18 F-FDG were key factors for general use in oncology and other fields. More recently, 82 Rb found widespread applications in myocardial perfusion studies (6), and 68 Ga has been extensively used for somatostatin receptor imaging (7). Both are generator-produced and can therefore be used by PET centers without access to a cyclotron.The continuous evolution of PET is now bringing new applications for old positron-emitting isotopes. In oncology, molecular imaging is evolving from simply tracking the hypermetabolism of cancer cells into imaging target molecules specific to a unique mechanism, or monitoring and guiding medical therapy, as in immunotherapy and radioimmunotherapy (8,9). Monoclonal antibodies are growing dramatically as therapeutic target-specific agents (10); 124 I, 89 Zr, 86 Y, 76 Br, and 64 Cu have shown an excellent ability to label monoclonal antibodies, with half-lives matched to the rate of antibody accumulation in tumors or target organs. Another area of development is targeted radionuclide therapy-for example...