Tomosynthesis in Respiratory Medicine

In the field of respiratory medicine, chest radiography and chest CT have to date been the main modalities of imaging used in routine medical care. The word tomosynthesis is formed from tomography and synthesis, tomosynthesis is a kind of digital tomography which is an imaging modality capable of reconstructing a coronal plane section of arbitrary height from a single tomographic scan 1) . The principle of tomosynthesis was announced by Ziedes des Plantes in 1938, and the first application of tomosynthesis in medical science was reported by Miller et al in 1971 2) 3) . In Japan, system developed at Shinshu University in 1989 4) was subsequently refined and, in the middle of the 2000s, introduced by Shimadzu as a tomography system equipped with a direct-conversion flat panel detector (FPD) where the issue of distortion of the light receiving surface had been resolved 5) . While it is mainly CT and MRI that are used in all fields including respiratory medicine, when used with a high-resolution FPD, tomosynthesis is also capable of high-definition tomographic images and as such has come to be used in orthopedics in particular. In the field of respiratory medicine that we are engaged in, recent research has shown these tomographic images are superior at showing nodules compared to chest radiography 6) . The exposure dose of tomosynthesis is equivalent to performing several chest radiography scans or around one-tenth exposure dose of a chest CT scan, and system installation space is smaller than a chest CT system. In light of this, tomosynthesis can be described as positioned within the field of respiratory medicine in-between chest radiography and chest CT. Table 1 shows the respective characteristics of chest radiography, chest tomosynthesis, and chest CT. Shimadzu SONIALVISION safire series was introduced as one of the hospital's FPD-equipped R/F systems, and between June 2012 and October 2013, the SONIALVISION safire series was used for tomosynthesis in 540 cases of respiratory disorders (counting only cases of respiratory medicine). This article reviews tomosynthesis in the field of respiratory medicine based on experience and results obtained at the National Cancer Center Hospital.