Feasibility of shortening the ¹⁸F-FDG Patlak scan time in a high-sensitivity short-axial field-of-view positron...

The net influx rate (K _i), a quantitative metric that complements the standardized uptake value (SUV), entails certain limitations, including its long acquisition time in clinical practice. This study aimed to investigate the clinical practicability of ¹⁸F fluorodeoxyglucose (¹⁸F-FDG) Patlak imaging in a high-sensitivity short-axial positron emission tomography-computed tomography (PET/CT) scanner by comparing various Patlak protocols alongside the application of a deep learning-based denoising algorithm.

This study included 14 patients who received a dual-time injection of ¹⁸F-FDG. Four virtual scans were generated with two injections and the scan time ranging from 0 to 86 min. The second scan was conducted 80 min after the first scan. Protocols had varying scan durations-0-75, 0-40 and 41-75, 41-75 and 80-86, and 41-75 min-which were defined as protocols 1, 2, 3, and 4, respectively. Four protocols were generated to account for different arterial input functions (AIFs), and whole-body (WB) passes (3, 4, 5, 6, and 7 passes × 5 min/pass) obtained between 41 and 75 min after the injection were used for Patlak fitting after denoising. Bland-Altman analysis was performed to compare the four AIF protocols in K _i values in FDG-avid lesions and to analyze the impact of the number of WB passes on K _i values. Additionally, Pearson correlation of K _i values between the abbreviated protocols (protocols 2, 3, and 4) and the standard protocol (protocol 1) was performed.

Fourteen participants completed the standard Patlak protocol (0-75 min), while 12 completed the full dual-injection protocol (0-86 min) required for all AIF methods. Two participants did not complete the full protocol due to physical discomfort from prolonged lying. Compared to the image-derived input function (IDIF) of the standard protocol, the abbreviated protocols exhibited a relatively lower area under the curve (AUC). K _i values demonstrated good agreement and high correlation between different protocols, with r values ranging from 0.9451 to 1.0000. In comparison to the estimation obtained from protocol 1, protocol 4, derived from the population-based input function (PBIF) with 20 min of PET (i.e., 55 to 75 min after injection), yielded <3% bias and <15% precision error for K _i in tumor lesions. The K _i images acquired with different protocols were visually equivalent.

The findings suggest that abbreviated protocols can provide acceptable K _i from short-axial PET/CT systems. The 20-min PBIF-based protocol, enhanced by a deep learning-based denoising algorithm, demonstrated the potential to be applied in K _i analysis for both scientific and clinical purposes.