**3. Digital image processing of dent-maxillofacial radiographs**

Digital panoramic radiography (DPR) and cone-beam-type of computed tomography (CBCT) were developed and patented by Nihon University School of Dentistry in the late 1980s and 1990s, respectively [10] (**Figure 2**). These technologies were transferred to Morita Corporation (Kyoto).

Regarding CBCT, Nihon University School of Dentistry obtained the Kinki Bureau of International Trade and Industry Regional New Industry Creation Technology Development Subsidy (1997–1999) to develop a commercial machine and pharmaceutical approval in 2001. CBCT allows three-dimensional diagnostic imaging of the teeth and inner ear. The National Health Insurance has covered it since 2012 in Japan, and since then, it has become an essential diagnostic imaging in dental care. Presently, CBCT machines are available at a rate of 1 per 10,000 people in Japan. We have installed the Veraviewepocs R100, a model of CBCT, at the University of Health

#### **Figure 2.**

*Schematic diagram of the CBCT device used in this study. Left: measurement principle. Right: maxillofacial tomographic image. These figures are taken from Ref. [10].*

Sciences (UHS). Veraviewepocs R100 can be used to perform panoramic tomography and CBCT. This CBCT has four types of fields of view (FOV): diameter of 4 cm and height of 4 cm, 4 cm × 8 cm, 8 cm × 8 cm and 10 cm× 8 cm. The optimal size of FOV was selected according to the purpose of diagnosis.

When FOV with a diameter of 4 cm and height of 4 cm is used, its dose is several times that of panoramic tomography but only approximately 1/100 that of conventional CT.

The spatial resolution of CBCT is calculated via the modulation transfer function using the wire method. It was as good as >10% at 2.0-line pair/mm. It was few times higher than that of conventional CT.

As described above, this device was characterized by low radiation dose and high resolution. It was optimized for dental practice. Currently, it has been further improved and provides detailed views of very fine anatomical structures in the head and neck, such as the temporal bone, paranasal sinus, eye sockets, jaw, and skull base. Consequently, it can be used for ENT (ear, nose, and throat) and plastic surgery, and all dental indications.
