title: Clinical Evaluation of PET Image Quality as a Function of Acquisition Time in a New TOF-PET/MRI Compared to TOF-PET/CT--Initial Results.
abstract: OBJECTIVE
  The purpose of this study was to compare only the performance of the PET component between a TOF-PET/CT (henceforth noted as PET/CT) scanner and an integrated TOF-PET/MRI (henceforth noted as PET/MRI) scanner concerning image quality parameters and quantification in terms of standardized uptake value (SUV) as a function of acquisition time (a surrogate of dose). The CT and MR image quality were not assessed, and that is beyond the scope of this study.
  
  
  METHODS
  Five brain and five whole-body patients were included in the study. The PET/CT scan was used as a reference and the PET/MRI acquisition time was consecutively adjusted, taking into account the decay between the scans in order to expose both systems to the same amount of the emitted signal. The acquisition times were then retrospectively reduced to assess the performance of the PET/MRI for lower count rates. Image quality, image sharpness, artifacts, and noise were evaluated. SUV measurements were taken in the liver and in the white matter to compare quantification.
  
  
  RESULTS
  Quantitative evaluation showed strong correlation between PET/CT and PET/MRI brain SUVs. Liver correlation was good, however, with lower uptake estimation in PET/MRI, partially justified by bio-redistribution. The clinical evaluation showed that PET/MRI offers higher image quality and sharpness with lower levels of noise and artifacts compared to PET/CT with reduced acquisition times for whole-body scans while for brain scans there is no significant difference.
  
  
  CONCLUSIONS
  The TOF-PET/MRI showed higher image quality compared to TOF-PET/CT as tested with reduced imaging times. However, this result accounts mainly for body imaging, while no significant differences were found in brain imaging.
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland. konstantinos.zeimpekis@usz.ch.
authors.forename: Konstantinos G
authors.initials: KG
authors.lastname: Zeimpekis
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland.
authors.forename: Felipe
authors.initials: F
authors.lastname: Barbosa
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Hüllner
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland.
authors.forename: Edwin
authors.initials: E
authors.lastname: ter Voert
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland.
authors.forename: Helen
authors.initials: H
authors.lastname: Davison
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zürich, Switzerland.|Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Veit-Haibach
authors.affiliation: GE Healthcare, Waukesha, WI, USA.
authors.forename: Gaspar
authors.initials: G
authors.lastname: Delso
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging; D003952:Diagnostic Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D011829:Radiation Dosage; D051598:Whole Body Imaging
keywords: Dose reduction; Image quality; PET/CT; PET/MRI; Solid-state PET detectors; Time-of-flight
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