Three-dimensional clinical PET in lung cancer: Validation and practical strategies

The feasibility of 3-dimensional acquisition mode for semiquantitative anal ysis in thoracic PET studies was compared to the conventional 2-dimensional mode. Several practical considerations were analyzed to propose an optimiz ed scanning protocol for clinical use. Methods: Twenty-one patients with fo cal thoracic abnormalities were evaluated with FDG PET. The acquisition con sisted of 3 consecutive static scans for a single bed position: S-dimension al (10 min), 2-dimensional (15 min), and 3-dimensional (5 min). On the basi s of the average and maximum activity values per region of interest, standa rdized uptake value (SUV) normalized for total body weight (TBW), lean body mass (LBM), body surface area (BSA), and blood glucose level (PGL) were ev aluated. The effect of the delay between tracer injection and PET scanning on the SUV, as well as on the relative error of the activity distribution, was studied from 40-134 min after tracer injection. Results: A strong posit ive correlation was observed among SUVs from 2-dimensional and both 3-dimen sional acquisitions. The mean SUV percentage differences between both acqui sition modes were about 17%, differences that were not statistically signif icant when time postinjection was addressed in the analysis of covariance. SUVs provided the greatest variability and differences among studies on exp erimental periods up to 70 min postinjection. Indeed, the variability of 20 % observed on the SUVs from 2 PET scans 13 min apart was reduced to 9% when the acquisitions started at least 70 min after tracer injection. In additi on, a two-fold reduction in the relative error of the activity distribution was observed over this period of time. The reproducibility coefficient was increased from 0.87 to 0.95 before and after 70 min postinjection, respect ively. No correlation was found between different normalization procedures of SUV and LBM, BSA, TEW, or height, whereas a weak correlation was found b etween SUV and PGL, Conclusion: F-18-FDG 3-dimensional PET is a realistic a lternative to the gold standard 2-dimensional for clinical nonkinetic studi es. A short, 5-min 3-dimensional acquisition at 70 min postinjection is pro posed as the best protocol for the clinical evaluation of thoracic patholog ies.