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.

Imaging blood-brain barrier dysfunction: A state-of-the-art review from a clinical perspective

“…The use of serial scans with different radiotracers is limited by the risks associated with repeated exposure to ionizing radiation, but more importantly limited by the quantification approach for PET that requires serial arterial sampling of PET tracer distribution in blood for accurate quantification. However, integrated PET–MRI systems have emerged, reducing the radiation dose to the patient by eliminating CT for attenuation correction ( Box 1 ), as well as potentially obviating the need for invasive arterial blood sampling (image-derived input function ( Box 1 ) ( Dassanayake et al, 2021 ; Vestergaard et al, 2021 ).…”