title: Evaluation of the subtraction method utilizing posterior view for improving visibility of the sentinel lymph nodes for lymphoscintigraphy in breast cancer.
abstract: OBJECTIVE
  This study aimed to evaluate the usefulness of the subtraction method for improving sentinel lymph node (SLN) visibility by reducing scattering near the injection site.
  
  
  METHODS
  Images of two phantoms for the injection site and SLNs built using an original design were simultaneously acquired using a dual-head camera equipped with a low-energy high-resolution collimator on the lower detector (posterior view) and a low-energy general-purpose collimator on the upper detector (anterior view). Subtraction method images were created by subtracting the posterior view from the anterior view, the latter of which was designated as the conventional method. Image contrast was calculated from the counts of regions of interest placed on the two phantoms of the injection site and SLNs. SLNs visibility to a distance from the injection site and a radioactivity ratio based on the injection site (15 MBq) was evaluated by image contrast and visual interpretation.
  
  
  RESULTS
  The best improvement in contrast occurred at a distance of 20 pixels (1.08 mm/pixel) from the injection site, and improved further as the lymph node radioactivity was smaller. The SLN's visibility corresponding to a distance of 20 pixels improved significantly (p < 0.001), from 1/2560 of radioactivity at the injection site (approximately 6 kBq) to 1/640 (approximately 23 kBq), and the SLN was only detectable using the subtraction method. The SLN (1/5120, approximately 3 kBq) was difficult to detect even with the subtraction method, whereas the SLN with a ratio ≥1/320 (approximately 46 kBq) was easily detected even with the conventional method. These visibilities did not differ significantly between the two methods (p = 0.16 and >0.32, respectively). The subtraction method could detect SLNs near the tumor on clinical images.
  
  
  CONCLUSIONS
  The subtraction method improved SLN visibility near the injection site by reducing scattering from the injection site. Furthermore, an advantage of the subtraction method is that it does not require additional imaging, because the posterior view is obtained simultaneously and utilized.
authors: Division of Nuclear Medicine, Chiba Cancer Center, 666-2 Nitona, Chuoh-Ku, Chiba, 260-8717, Japan.|Department of Quantum Medical Technology, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa, 920-0942, Japan.
authors: Hironori
authors: H
authors: Ichihara
authors: Department of Quantum Medical Technology, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa, 920-0942, Japan. onoguchi@staff.kanazawa-u.ac.jp.
authors: Masahisa
authors: M
authors: Onoguchi
authors: Department of Radiological Technology, Faculty of Health Science, Hokkaido University of Science, 7-Jo 15-4-1 Maeda, Teine, Sapporo, Hokkaido, 006-8585, Japan.
authors: Akihiro
authors: A
authors: Kikuchi
authors: Department of Quantum Medical Technology, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa, 920-0942, Japan.
authors: Takayuki
authors: T
authors: Shibutani
mesh_terms: D016477:Artifacts; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D006801:Humans; D061305:Lymphoscintigraphy / Q000379:methods*; D012542:Scattering, Radiation; D000071036:Sentinel Lymph Node / Q000000981:diagnostic imaging*; D021701:Sentinel Lymph Node Biopsy; D059629:Signal-To-Noise Ratio; D013382:Subtraction Technique
keywords: Breast cancer; Lymphoscintigraphy; Sentinel lymph node