title: Geographic Distribution of CT, MRI and PET Devices in Japan: A Longitudinal Analysis Based on National Census Data.
abstract: BACKGROUND
  Japan has the most CT and MRI scanners per unit population in the world; however, the geographic distribution of these technologies is currently unknown. Moreover, nothing is known of the cause-effect relationship between the number of diagnostic imaging devices and their geographic distribution.
  
  
  METHODS
  Data on the number of CT, MRI and PET devices and that of their utilizations in all 1829 municipalities of Japan was generated, based on the Static Survey of Medical Institutions conducted by the government. The inter-municipality equity of the number of devices or utilizations was evaluated with Gini coefficient.
  
  
  RESULTS
  Between 2005 and 2011, the number of CT, MRI and PET devices in Japan increased by 47% (8789 to 12945), 19% (5034 to 5990) and 70% (274 to 466), respectively. Gini coefficient of the number of devices was largest for PET and smallest for CT (p for PET-MRI difference <0.001; MRI-CT difference <0.001). For all three modalities, Gini coefficient steadily decreased (p for 2011-2005 difference: <0.001 for CT; 0.003 for MRI; and <0.001 for PET). The number of devices in old models (single-detector CT, MRI<1.5 tesla, and conventional PET) decreased, while that in new models (multi-detector CT, MRI≥1.5 tesla, and PET-CT) increased. Gini coefficient of the old models increased or remained unchanged (increase rate of 9%, 3%, and -1%; p for 2011-2008 difference <0.001, 0.072, and 0.562, respectively), while Gini coefficient of the new models decreased (-10%, -9%, and -10%; p for 2011-2008 difference <0.001, <0.001, and <0.001 respectively). Similar results were observed in terms of utilizations.
  
  
  CONCLUSIONS
  The more abundant a modality, the more equal the modality's distribution. Any increase in the modality made its distribution more equal. The geographic distribution of the diagnostic imaging technology in Japan appears to be affected by spatial competition derived from a market force.
authors.affiliation: Department of Community-Based Medical System, Faculty of Medicine, Hiroshima University, Hiroshima, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Matsumoto
authors.affiliation: Division of Health Policy and Management, Center for Community Medicine, Jichi Medical University, Tochigi, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Koike
authors.affiliation: Department of Public Health and Health Policy, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Kashima
authors.affiliation: Department of Diagnostic Radiology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Awai
mesh_terms: D019352:Censuses; D054625:Healthcare Disparities / Q000706:statistics & numerical data; D006801:Humans; D007564:Japan; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D011156:Population Density; D049268:Positron-Emission Tomography / Q000706:statistics & numerical data*; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*