title: Fully automated calculation of image-derived input function in simultaneous PET/MRI in a sheep model.
abstract: BACKGROUND
  Obtaining the arterial input function (AIF) from image data in dynamic positron emission tomography (PET) examinations is a non-invasive alternative to arterial blood sampling. In simultaneous PET/magnetic resonance imaging (PET/MRI), high-resolution MRI angiographies can be used to define major arteries for correction of partial-volume effects (PVE) and point spread function (PSF) response in the PET data. The present study describes a fully automated method to obtain the image-derived input function (IDIF) in PET/MRI. Results are compared to those obtained by arterial blood sampling.
  
  
  METHODS
  To segment the trunk of the major arteries in the neck, a high-resolution time-of-flight MRI angiography was postprocessed by a vessel-enhancement filter based on the inertia tensor. Together with the measured PSF of the PET subsystem, the arterial mask was used for geometrical deconvolution, yielding the time-resolved activity concentration averaged over a major artery. The method was compared to manual arterial blood sampling at the hind leg of 21 sheep (animal stroke model) during measurement of blood flow with O15-water. Absolute quantification of activity concentration was compared after bolus passage during steady state, i.e., between 2.5- and 5-min post injection. Cerebral blood flow (CBF) values from blood sampling and IDIF were also compared.
  
  
  RESULTS
  The cross-calibration factor obtained by comparing activity concentrations in blood samples and IDIF during steady state is 0.98 ± 0.10. In all examinations, the IDIF provided a much earlier and sharper bolus peak than in the time course of activity concentration obtained by arterial blood sampling. CBF using the IDIF was 22 % higher than CBF obtained by using the AIF yielded by blood sampling.
  
  
  CONCLUSIONS
  The small deviation between arterial blood sampling and IDIF during steady state indicates that correction of PVE and PSF is possible with the method presented. The differences in bolus dynamics and, hence, CBF values can be explained by the different sampling locations (hind leg vs. major neck arteries) with differences in delay/dispersion. It will be the topic of further work to test the method on humans with the perspective of replacing invasive blood sampling by an IDIF using simultaneous PET/MRI.
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany. Thies.Jochimsen@medizin.uni-leipzig.de.
authors.forename: Thies H
authors.initials: TH
authors.lastname: Jochimsen
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Vilia
authors.initials: V
authors.lastname: Zeisig
authors.affiliation: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, Leipzig, D-04103, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Schulz
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Werner
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Marianne
authors.initials: M
authors.lastname: Patt
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Patt
authors.affiliation: Fraunhofer Institute of Cell Therapy and Immunology, Perlickstr. 1, Leipzig, D-04103, Germany.|Translational Centre for Regenerative Medicine, University Leipzig, Philipp-Rosenthal-Str. 55, Leipzig, D-04103, Germany.
authors.forename: Antje Y
authors.initials: AY
authors.lastname: Dreyer
authors.affiliation: Fraunhofer Institute of Cell Therapy and Immunology, Perlickstr. 1, Leipzig, D-04103, Germany.|Translational Centre for Regenerative Medicine, University Leipzig, Philipp-Rosenthal-Str. 55, Leipzig, D-04103, Germany.|Fraunhofer Research Institution of Marine Biotechnology and Institute for Medical and Marine Biotechnology, University of Lübeck, Lübeck, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Boltze
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Henryk
authors.initials: H
authors.lastname: Barthel
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Osama
authors.initials: O
authors.lastname: Sabri
authors.affiliation: Department of Nuclear Medicine, Leipzig University Hospital, Liebigstr. 18, Leipzig, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Sattler
keywords: Angiography; Arterial input function; Image-derived input function; PET/MRI