title: Elimination of scattered gamma rays from injection sites using upper offset energy windows in sentinel lymph node scintigraphy.
abstract: OBJECTIVE
  The identification of sentinel lymph nodes (SLNs) near injection sites is difficult because of scattered gamma rays. The purpose of this study was to investigate the optimal energy windows for elimination of scattered gamma rays in order to improve the detection of SLNs.
  
  
  METHODS
  The clinical study group consisted of 56 female patients with breast cancer. While the energy was centred at 140 keV with a 20% window for Tc-99m, this energy window was divided into five subwindows with every 4% in planar imaging. Regions of interest were placed on SLNs and the background, and contrast was calculated using a standard equation. The confidence levels of interpretations were evaluated using a five-grade scale.
  
  
  RESULTS
  The contrast provided by 145.6 keV±2% was the best, followed by 140 keV±2%, 151.2 keV±2%, 134.4 keV±2% and 128.8 keV±2% in that order. When 128.8 keV±2% and 134.4 keV±2% were eliminated from 140 keV±10% (145.6 keV±6%), the contrast of SLNs improved significantly. The confidence levels of interpretation and detection rate provided by the planar images with 140 keV±10% were 4.74±0.58 and 94.8%, respectively, and those provided by 145.6 keV±6% were 4.94±0.20 and 100%.
  
  
  CONCLUSIONS
  Because lower energy windows contain many scattered gamma rays, upper offset energy windows, which exclude lower energy windows, improve the image contrast of SLNs near injection sites.
authors.affiliation: aDepartment of Radiological Technology, Kanazawa University Hospital Departments of bHealth Science cBiotracer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa dDepartment of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Yoneyama
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tsushima
authors.forename: Masahisa
authors.initials: M
authors.lastname: Onoguchi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Konishi
authors.forename: Kenichi
authors.initials: K
authors.lastname: Nakajima
authors.forename: Seigo
authors.initials: S
authors.lastname: Kinuya
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging; D005260:Female; D005720:Gamma Rays; D006801:Humans; D007267:Injections; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008875:Middle Aged; D011877:Radionuclide Imaging / Q000379:methods*; D012542:Scattering, Radiation