title: Quantitative comparison between regularized time-of-flight and OSEM PET reconstructions for small 18F-FDG-avid lesions.
abstract: OBJECTIVE
  We seek to quantitatively assess the relationship between lesion size and maximum standard uptake value (SUVmax) differences for small fluorine-18-fluorodeoxyglucose-avid lesions through the comparison of regularized time-of-flight (R-ToF) PET and standard ordered subset expectation maximization (OSEM) PET reconstructions.
  
  
  METHODS
  Data from 30 patients (male to female ratio 8 : 7, 15 different primary malignancies) who underwent noncontrast PET-CT in October 2015 through February 2016 were evaluated. For each patient, multiple reconstructions of the PET data, including R-ToF, time-of-flight (ToF), and non-ToF, were constructed using OSEM of three iterations and 24 subsets. Volumes of interest were contoured for lesions up to 3 cm in size, and SUVmax measurements and lesion size were recorded for a total of 64 lesions. Liver measurements were also recorded for background analysis. A comparative statistical analysis was subsequently carried out.
  
  
  RESULTS
  R-ToF showed the highest SUVmax for all 64 lesions and the highest SUVmax mean (P<0.0001) among all lesions, followed by ToF and non-ToF. R-ToF also showed a statistically significant negative correlation (P<0.001) between lesion size and SUVmax versus ToF and non-ToF PET; the smaller the lesion, the greater the disparity. R-ToF also showed the largest mean background signal to noise ratio (P<0.0001), mean lesion signal to noise ratio (P<0.001), and mean lesion signal to background ratio (P<0.0001) versus ToF and non-ToF PET.
  
  
  CONCLUSIONS
  R-ToF shows higher SUVmax values than standard OSEM reconstructions for all fluorine-18-fluorodeoxyglucose -avid lesions, with greater differences for increasingly smaller lesions. R-ToF offers improved suppression of background noise versus OSEM and therefore increased signal to noise and background ratios. These findings offer potential for improved small lesion visibility and characterization.
authors.affiliation: aDepartment of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston bDepartment of Nuclear Medicine cDepartment of Imaging Physics, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Chism
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Ravizzini
authors.forename: Homer A
authors.initials: HA
authors.lastname: Macapinlac
authors.forename: Tinsu
authors.initials: T
authors.lastname: Pan
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D019788:Fluorodeoxyglucose F18