title: Improvement of the diagnostic accuracy of lymph node metastases of colorectal cancer in 18F-FDG-PET/CT by optimizing the iteration number for the image reconstruction.
abstract: OBJECTIVE
  Improvement in the diagnostic accuracy of lymph node (LN) metastases of colorectal cancer by optimizing the reconstruction parameters was studied, including a phantom study and clinical studies.
  
  
  METHODS
  In the experimental study, the contrast ratio was evaluated using a standard image quality phantom, changing the iteration number of ordered subsets expectation maximization algorithm from 2 to 6. In the clinical study, 89 patients with preoperative colorectal cancer who received 18F-2-deoxy-2-fluoro-D: -glucose positron emission tomography/computed tomography (PET/CT) were studied. Their LN metastases were visually assessed when systematically changing the iteration number, and the optimal iteration number was determined. After the appropriate cut-off value of maximum standardized uptake value was determined, the improvement of the diagnostic accuracy of LN metastases was evaluated for the proximal nodes and the distal ones using the reconstructed images with the optimal iteration number. This was compared with the conventional method that had an iteration number of 2.
  
  
  RESULTS
  In the phantom study, it was confirmed that the contrast ratio improved when the iteration number increased. In clinical evaluation, the optimal iteration number was determined to be 5 by visual assessment. When the cut-off value of 1.5 was used, which happened to be the best number, the sensitivity/specificity/accuracy improved from 52%/91%/72% to 77%/89%/83% for the proximal nodes, and from 63%/90%/84% to 91%85%/87% for the distal nodes, respectively.
  
  
  CONCLUSIONS
  When the iteration number of the reconstruction algorithm was optimized, the sensitivity of LN metastasis improved by more than 20%, and the accuracy exceeded 80%. Optimization of the image reconstruction parameters in the diagnosis of LN metastases using PET/CT is clinically important.
authors.affiliation: Graduate School of Health Science, Tokyo Metropolitan University, Tokyo, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Inoue
authors.forename: Takashi
authors.initials: T
authors.lastname: Sato
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kitamura
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ito
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsunoda
authors.forename: Akira
authors.initials: A
authors.lastname: Hirayama
authors.forename: Hideo
authors.initials: H
authors.lastname: Kurosawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Fukushi
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Moriyama
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Fujii
mesh_terms: D000465:Algorithms; D015179:Colorectal Neoplasms / Q000175:diagnosis*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18