title: Evaluation of the Effect of Tumor Position on Standardized Uptake Value Using Time-of-Flight Reconstruction and Point Spread Function.
abstract: OBJECTIVE
  The present study was conducted to examine whether the standardized uptake value (SUV) may be affected by the spatial position of a lesion in the radial direction on positron emission tomography (PET) images, obtained via two methods based on time-of-flight (TOF) reconstruction and point spread function (PSF).
  
  
  METHODS
  A cylinder phantom with the sphere (30 mm diameter), located in the center was used in this study. Fluorine-18 fluorodeoxyglucose (18F-FDG) concentrations of 5.3 kBq/ml and 21.2 kBq/ml were used for the background in the cylinder phantom and the central sphere respectively. By the use of TOF and PSF, SUVmaxand SUVmeanwere determined while moving the phantom in a horizontal direction (X direction) from the center of field of view (FOV: 0 mm) at 50, 100, 150 and 200 mm positions, respectively. Furthermore, we examined 41 patients (23 male, 18 female, mean age: 68±11.2 years) with lymph node tumors, who had undergone18F-FDG PET examinations. The distance of each lymph node from FOV center was measured, based on the clinical images.
  
  
  RESULTS
  As the distance of a lesion from the FOV center exceeded 100 mm, the value of SUVmax, which was obtained with the cylinder phantom, was overestimated, while SUVmeanby TOF and/or PSF was underestimated. Based on the clinical examinations, the average volume of interest was 8.5 cm3. Concomitant use of PSF increased SUVmaxand SUVmeanby 27.9% and 2.8%, respectively. However, size of VOI and distance from the FOV center did not affect SUVmaxor SUVmeanin clinical examinations.
  
  
  CONCLUSIONS
  The reliability of SUV quantification by TOF and/or PSF decreased, when the tumor was located at a 100 mm distance (or farther) from the center of FOV. In clinical examinations, if the lymph node was located within 100 mm distance from the center of FOV, SUV remained stable within a constantly increasing range by use of both TOF and PSF. We conclude that, use of both TOF and PSF may be helpful.
authors.affiliation: Division of Radiological Technology, Saitama Prefectural Cancer Center, Saitama, Japan; Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences, Gunma, Japan.
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Wakabayashi
authors.affiliation: Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences, Gunma, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kashikura
authors.affiliation: Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences, Gunma, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Division of Radiological Technology, Saitama Prefectural Cancer Center, Saitama, Japan; Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yabe
authors.affiliation: Division of Molecular Imaging, Saitama Prefectural Cancer Center, Saitama, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Ichikawa
authors.affiliation: Division of Radiological Technology, Saitama Prefectural Cancer Center, Saitama, Japan.
authors.forename: Souichi
authors.initials: S
authors.lastname: Yamamoto
authors.affiliation: Division of Radiological Technology, Saitama Prefectural Cancer Center, Saitama, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Ishii
authors.affiliation: Department of Radiology, University of Chicago, Chicago, Illinois, USA.
authors.forename: Kunio
authors.initials: K
authors.lastname: Doi
keywords: 18F-FDG; Point spread function; Standardized Uptake Value; Time-of-flight; Tumor size