Geographic Distribution of CT, MRI and PET Devices in Japan: A Longitudinal Analysis Based on National Census Data

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.研究背景 日本是全球单位人口拥有CT（计算机断层扫描，Computed Tomography）与MRI（磁共振成像，Magnetic Resonance Imaging）扫描仪数量最多的国家，但目前这类设备的地理分布情况仍不明确。此外，诊断成像设备的数量与其地理分布之间的因果关系也尚未可知。 研究方法 本研究基于日本政府开展的《医疗机构静态调查》（Static Survey of Medical Institutions），获取了日本全国1829个市町村的CT、MRI、PET（正电子发射断层扫描，Positron Emission Tomography）设备数量及使用量数据。采用基尼系数（Gini coefficient）评估各设备数量或使用量在市町村间的分布公平性。 研究结果 2005年至2011年间，日本CT、MRI及PET设备的数量分别增长了47%（从8789台增至12945台）、19%（从5034台增至5990台）与70%（从274台增至466台）。设备数量的基尼系数以PET最高、CT最低（PET与MRI的组间差异p<0.001；MRI与CT的组间差异p<0.001）。三类设备的基尼系数均呈持续下降趋势（2011年与2005年的差异：CT组p<0.001，MRI组p=0.003，PET组p<0.001）。 老旧型号设备（单排探测器CT、场强低于1.5特斯拉的MRI及传统PET）的数量有所减少，而新型号设备（多排探测器CT、场强≥1.5特斯拉的MRI及PET-CT）的数量则呈增长态势。老旧型号设备的基尼系数有所上升或保持不变（2011年与2008年的变化率分别为9%、3%与-1%，对应p值分别为<0.001、0.072与0.562）；新型号设备的基尼系数则呈下降趋势（变化率分别为-10%、-9%与-10%，2011年与2008年的差异均p<0.001）。设备使用量方面也观测到了相似的结果。 研究结论 某类诊断成像设备的保有量越高，其地理分布的公平性越强。设备保有量的提升均会改善其分布的公平性。日本诊断成像技术的地理分布似乎受到市场力量驱动的空间竞争影响。