title: Effect of attenuation correction on lesion detection using a hybrid PET system.
abstract: OBJECTIVE
  The purpose of this study was to investigate the effect of attenuation correction (AC) on lesion detection for a hybrid PET system.
  
  
  METHODS
  Experimental list-mode data were acquired from hot spheres inside a uniform cylindrical phantom with an elliptical cross-section using a Siemens E. CAM+ dual-camera hybrid PET system. Spheres with inner diameters of 0.8- and 1-cm and the cylindrical phantom were filled with F-18 to simulate lesions with lesion-to-background (L/B) ratios of 14:1 and 8:1, respectively, found in clinical PET studies. The list-mode data of each sphere size were regrouped into sinograms with peak-to-peak energy window settings at 30% and 20% for the 0.8- and 1-cm diameter lesion, respectively. They were then rebinned using the single slice rebinning method. Attenuation correction was applied assuming uniform attenuation. The sinograms with and without AC were reconstructed using 5 iterations of OS-EM algorithm with 8 angles/ subset and postfiltered with a Butterworth filter with n = 5 and fc = 0.52 cycles/cm. Human observer performance study and localization receiver operating characteristic (LROC) analysis were used to evaluate the reconstructed images for maximum lesion detection. Average areas under the LROC curves (A(LROC)) across 8 observers obtained with and without AC were determined. The null hypothesis that there was no difference between with AC and without AC was tested using a two-tailed t-test with 95% confidence interval.
  
  
  RESULTS
  The results indicated that for the 0. 8-cm lesion with 14:1 L/B ratio, the A(LROC) decreases from 0.66 to 0.62 when AC is applied as compared to without AC andfrom 0.69 to 0.63 for the 1.0-cm lesion with 8:1 L/ B ratio, but no statistical significant difference (p > 0. 05).
  
  
  CONCLUSIONS
  The authors conclude that for a phantom with hot lesions embedded in a uniform background, AC decreases lesion detectability compared to without AC using a hybrid PET system for small lesion sizes.
authors.affiliation: Department of Radiological Technology, Faculty of Medical Technology, Mahidol University, Bangkok 10700, Thailand.
authors.forename: Chiraporn
authors.initials: C
authors.lastname: Tocharoenchai
authors.forename: Benjamin M W
authors.initials: BM
authors.lastname: Tsui
authors.forename: Eric C
authors.initials: EC
authors.lastname: Frey
authors.forename: Wen-Tung
authors.initials: WT
authors.lastname: Wang
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D009369:Neoplasms / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D012372:ROC Curve; D011859:Radiography