Noninvasive Input Function Acquisition and Simultaneous Estimations With Physiological Parameters for PET Quantification: A Brief Review

The recent introduction of high-resolution and high-speed PET/CT is making noninvasive absolute quantification of physiological function more convenient and feasible. A key issue for absolute quantification is the accurate estimation of the time-activity curve (TAC) in plasma (PTAC). We provide a brief survey of the population-based and the image-derived PTAC approaches together with their performance characterizations. We then give a summary of the recent report on the image-derived PTAC from the first total-body PET/CT device, uEXPLORER. We finally summarize the kinetic model-based simultaneous estimation of input functions and physiological parameters (SIME) method. SIME has several advantages, including the more adequately estimated local input function for adjacent tissue TACs; simultaneous correction of spillover and partial-volume effect; smoothing the measurement noise and alleviating the need for the measurement of the PTAC peak; and simultaneous estimation of multiple input functions for organs such as the liver where blood is supplied from the hepatic artery and the portal vein. As the SIME approach is intended to improve the quality of quantification, it is expected that the image-derived PTAC from the total-body PET scanner together with the SIME approach will advance future PET absolute quantitative studies.