title: Patient-specific optimisation of administered activity and acquisition times for18F-FDG PET imaging.
abstract: BACKGROUND
  The purpose of this study is to identify a method for optimising the administered activity and acquisition time for18F-FDG PET imaging, yielding images of consistent quality for patients with varying body sizes and compositions, while limiting radiation doses to patients and staff. Patients referred for FDG scans had bioimpedance measurements. They were injected with 3 MBq/kg of18F up to 370 MBq and scanned on a Siemens Biograph mCT at 3 or 4 min per bed position. Data were rebinned to simulate 2- and 1-min acquisitions. Subjective assessments of image quality made by an experienced physician were compared with objective measurements based on signal-to-noise ratio and noise equivalent counts (NEC). A target objective measure of image quality was identified. The activity and acquisition time required to achieve this were calculated for each subject. Multiple regression analysis was used to identify expressions for the activity and acquisition time required in terms of easily measurable patient characteristics.
  
  
  RESULTS
  One hundred and eleven patients were recruited, and subjective and objective assessments of image quality were compared for 321 full and reduced time scans. NEC-per-metre was identified as the objective measure which best correlated with the subjective assessment (Spearman rank correlation coefficient 0.77) and the best discriminator for images with a subjective assessment of "definitely adequate" (area under the ROC curve 0.94). A target of 37 Mcount/m was identified. Expressions were identified in terms of patient sex, height and weight for the activity and acquisition time required to achieve this target. Including measurements of body composition in these expressions was not useful. Using these expressions would reduce the mean activity administered to this patient group by 66 MBq compared to the current protocol.
  
  
  CONCLUSIONS
  Expressions have been identified for the activity and acquisition times required to achieve consistent image quality in FDG imaging with reduced patient and staff doses. These expressions might need to be adapted for other systems and reconstruction protocols.
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK. Caspar.Wickham@nhs.net.
authors.forename: Fred
authors.initials: F
authors.lastname: Wickham
authors.affiliation: Hermes Medical Solutions, 22 Long Acre, London, WC2E 9LY, UK.
authors.forename: Helena
authors.initials: H
authors.lastname: McMeekin
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK.
authors.forename: Maria
authors.initials: M
authors.lastname: Burniston
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: McCool
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK.
authors.forename: Deborah
authors.initials: D
authors.lastname: Pencharz
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK.
authors.forename: Annah
authors.initials: A
authors.lastname: Skillen
authors.affiliation: Nuclear Medicine Department, Royal Free London NHS Foundation Trust, Pond Street, London, NW3 2QG, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wagner
keywords: Acquisition time; Administered activity; Image quality; Noise equivalent counts; Optimisation; Positron emission tomography