title: Simultaneous emission and transmission measurements for attenuation correction in whole-body PET.
abstract: We describe a methodology for measuring and correcting for attenuation in whole-body PET using simultaneous emission and transmission (SET) measurements.
  
  
  METHODS
  The main components of the methodology are: (a) sinogram windowing of low activity (< or = 50 MBq) rotating 68Ge/Ga rod sources, (b) segmented attenuation correction (SAC) and (c) maximum likelihood reconstruction using the ordered subsets EM (OS-EM) algorithm. The methods were implemented on a whole-body positron emission tomograph. Quantitative accuracy and the signal-to-noise ratio (SNR) were measured for a thorax-tumor phantom as functions of acquisition time (range: 2-20 min per position).
  
  
  RESULTS
  When a typical rod source activity (200 MBq 68Ge/Ga) was used, emission SNR was 60% lower in simultaneous than in separate measurements. The difference was only 14% when the rods contained 45 MBq 68Ge/Ga. The SNR was further improved by SAC in conjunction with OS-EM reconstruction and the relative gain increased with increasing acquisition time. Quantitative estimates of tumor, liver and lung radioactivity agreed with values obtained from a separate high count measurement to within 8%, independent of acquisition time.
  
  
  CONCLUSIONS
  Attenuation correction of whole-body PET images is feasible using SET measurements. There is good quantitative agreement with conventional methods and increased noise is offset by the use of SAC and OS-EM reconstruction.
authors.affiliation: PET Department, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: S R
authors.initials: SR
authors.lastname: Meikle
authors.forename: D L
authors.initials: DL
authors.lastname: Bailey
authors.forename: P K
authors.initials: PK
authors.lastname: Hooper
authors.forename: S
authors.initials: S
authors.lastname: Eberl
authors.forename: B F
authors.initials: BF
authors.lastname: Hutton
authors.forename: W F
authors.initials: WF
authors.lastname: Jones
authors.forename: R R
authors.initials: RR
authors.lastname: Fulton
authors.forename: M J
authors.initials: MJ
authors.lastname: Fulham
mesh_terms: D000328:Adult; D005260:Female; D005710:Gallium Radioisotopes; D005857:Germanium; D006801:Humans; D008961:Models, Structural; D011868:Radioisotopes; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging; D014055:Tomography, Emission-Computed / Q000379:methods*
chemical_list: D005710:Gallium Radioisotopes; D011868:Radioisotopes; D005857:Germanium