Whole-body dynamic multiparametric PET/CT: temporal stability of standardized uptake values vs. metabolic rates in an oncologic population

1371 Introduction: Conventional SUV images depend on uptake period length, which often varies between scans and institutions. Furthermore, physiologic uptake of F-18 fluorodeoxyglucose (FDG) in organs, such as the liver, can limit detection of lesions with relatively low FDG-avidity. To address these shortcomings, the Patlak model estimates the metabolic rate (Ki), a marker of how quickly a PET tracer is irreversibly trapped in tissues. Although Ki images permit the assessment of tracer avidity in a relatively time-independent fashion, the Patlak approach has been difficult to implement clinically. The Siemens Vision PET/CT scanner, acquires whole-body dynamic PET data with high temporal resolution, performs direct parametric reconstruction to generate Ki images utilizing a dedicated Patlak acquisition protocol. In an oncology population, we assessed the temporal stability of SUV and Ki tumor metrics and the tumor-to-liver ratios for SUV and Ki images, as a part of a larger study evaluating the clinical impact of multiparametric PET/CT. Methods: To date, this prospective study has enrolled 18 subjects with cancer at various phases of treatment. Recruited from a population already scheduled to undergo clinically indicated PET/CT imaging, all subjects were ≥18 y/o and provided written informed consent. All subjects were imaged with FDG on a single Biograph Vision (Siemens Healthineers) PET/CT scanner. Beginning with tracer injection, a 6 min dynamic cardiac PET acquisition was performed to derive an arterial input function, followed by multiple whole-body dynamic passes utilizing continuous bed motion before and after a single standard-of-care (SOC) whole-body pass at ~60-75 min post-injection (p.i.). The last three 5 min pre-SOC passes (~30-45 min p.i.) and the three 5 min post-SOC passes (~80-95 min p.i.) were visually assessed for bulk motion and then utilized to reconstruct pre-SOC (early) and post-SOC (late) Ki and SUV images. Various Ki and SUV metrics were extracted for tumors (one per subject) and liver with MIM software. Statistical comparisons were based on the Wilcoxon signed-rank test (α = 0.05). Results: The 10 of 18 subjects with identifiable FDG-avid tumors were considered in the following analysis. All data reported are medians [interquartile ranges]. Units for Ki are mg/min/100ml. There were no significant differences in the early versus late time point (Figure) for tumor Ki-max (2.0 [1.0] v. 1.9 [1.9]; p = 0.65) or tumor Ki-peak (1.3 [0.8] v. 1.2 [1.2]; p = 0.24). In contrast, there were significant increases from the early to late time point (Figure) in tumor SUV-max (6.3 [3.2] v. 8.7 [6.6]; p = 0.005) and tumor SUV-peak (4.1 [2.4] v. 4.9 [5.1]; p = 0.02). Across all subjects, the relative change between early and late time points was significantly higher for tumor SUV-max than for tumor Ki-max (49% [38%] v. 13% [37%]; p = 0.009). The tumor Ki-max to liver Ki-mean ratio was higher than the tumor SUV-max to liver SUV-mean ratio at the early time point (3.9 [3.7] v. 1.9 [1.2]; p = 0.005) but lower at the late time point (2.4 [2.8] v. 3.2 [2.6]; p = 0.005). Conclusion: In an oncology population, tumor Ki-max and Ki-peak are more stable over time than SUV-max and SUV-peak. Furthermore, Ki images display greater tumor signal relative to the liver during the early uptake period than SUV images. Thus, multiparametric PET/CT has the potential to reduce quantitative variability and improve liver lesion detection.