CALIPER: A software for blood-free parametric Patlak mapping using PET/MRI input function

Abstract

Routine clinical use of absolute PET quantification techniques is limited by the need for serial arterial blood sampling for input function and more importantly by the lack of automated pharmacokinetic analysis tools that can be readily implemented in clinic with minimal effort. PET/MRI provides the ability for absolute quantification of PET probes without the need for serial arterial blood sampling using image-derived input functions (IDIFs). Here we introduce CALIPER, a tool for simplified pharmacokinetic modelling of PET probes with irreversible uptake or binding based on and PET/MR IDIFs and Patlak Plot analysis. CALIPER generates regional values or parametric maps of net influx rate (Ki) for tracers using reconstructed dynamic PET images and anatomical MRI for IDIF vessel delineation. We evaluated the performance of CALIPER for blood-free region-based and pixel-wise Patlak analyses of [18F]FDG. IDIFs corrected for partial volume errors including spill-out and spill-in effects were similar to AIF with a general bias of around 6-8%, even for arteries <5 mm. The Ki and cerebral metabolic rate of glucose estimated using IDIF were similar to estimates using blood sampling (<2%) and within limits of whole brain values reported in literature. Overall, CALIPER is a promising tool for irreversible PET tracer quantification and can simplify the ability to perform parametric analysis in clinical settings without the need for blood sampling.