title: Point-spread function reconstructed PET images of sub-centimeter lesions are not quantitative.
abstract: BACKGROUND
  PET image reconstruction methods include modeling of resolution degrading phenomena, often referred to as point-spread function (PSF) reconstruction. The aim of this study was to develop a clinically relevant phantom and characterize the reproducibility and accuracy of high-resolution PSF reconstructed images of small lesions, which is a prerequisite for using PET in the prediction and evaluation of responses to treatment. Sets of small homogeneous18F-spheres (range 3-12 mm diameter, relevant for small lesions and lymph nodes) were suspended and covered by a11C-silicone, which provided a scattering medium and a varying sphere-to-background ratio. Repeated measurements were made on PET/CT scanners from two vendors using a wide range of reconstruction parameters. Recovery coefficients (RCs) were measured for clinically used volume-of-interest definitions.
  
  
  RESULTS
  For non-PSF images, RCs were reproducible and fell monotonically as the sphere diameter decreased, which is the expected behavior. PSF images converged slower and had artifacts: RCs did not fall monotonically as sphere diameters decreased but had a maximum RC for sphere sizes around 8 mm, RCs could be greater than 1, and RCs were less reproducible. To some degree, post-reconstruction filters could suppress PSF artifacts.
  
  
  CONCLUSIONS
  High-resolution PSF images of small lesions showed artifacts that could lead to serious misinterpretations when used for monitoring treatment response. Thus, it could be safer to use non-PSF reconstruction for quantitative purposes unless PSF reconstruction parameters are optimized for the specific task.
authors.affiliation: Department of Nuclear Medicine & PET Centre, Aarhus University Hospital, Aarhus, Denmark. olelajmu@rm.dk.
authors.forename: O L
authors.initials: OL
authors.lastname: Munk
authors.affiliation: Department of Nuclear Medicine & PET Centre, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: L P
authors.initials: LP
authors.lastname: Tolbod
authors.affiliation: Department of Nuclear Medicine & PET Centre, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: S B
authors.initials: SB
authors.lastname: Hansen
authors.affiliation: Department of Nuclear Medicine & PET Centre, Aarhus University Hospital, Aarhus, Denmark.|Department of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway.
authors.forename: T V
authors.initials: TV
authors.lastname: Bogsrud
keywords: Image artifacts; Point spread function; Positron emission tomography; Quantitative imaging; Reconstruction; Standardized uptake value (SUV)