ORIGINAL ARTICLE Oral Radiol (2005) 21:14–18 © Japanese Society for Oral and Maxillofacial Radiology and Springer-Verlag Tokyo 2005 DOI 10.1007/s11282-005-0024-5 Yoshinori Arai · Ayuta Yamada · Tadashi Ninomiya Takafumi Kato · Yuji Masuda Micro-computed tomography newly developed for in vivo small animal imaging Received: October 22, 2004 / Accepted: January 6, 2005 Abstract Objectives. The aim of this paper is to report a newly devel- oped micro-computed tomography system for in vivo use. Methods. The system was composed of a micro-focus X-ray tube and an image intensifier (I.I.), both of which rotated around the object stage. A guinea pig and a rat were exam- ined. The anesthetized animal was set on the secure object stage. Images of the head of the guinea pig and the tibia/ knee joint of the rat were taken. In addition, an image of the rat’s tail was taken. The reconstruction and the image view- ing were carried out using I-View software. Results. The voxel matrix was 512 ¥ 512 ¥ 384. The voxel sizes ranged from 10 ¥ 10 ¥ 10 mm to 100 ¥ 100 ¥ 100 mm. The exposure time was 17 s, and the reconstruction time was 150 s. The head of the guinea pig and the tibia/knee joint of the rat were observed clearly under 100-mm and 30-mm voxels, respectively. The trabecular bone of the tail was also observed clearly under a 10-mm voxel. Conclusions. The newly developed micro-computed to- mography system makes it possible to obtain images of anesthetized animals set on a secure object stage. Clear bone images of the small animals could be obtained within a short time. Key words Micro-computed tomography · In vivo · Bone structure Introduction Micro-computed tomography (m CT) was developed for industrial use. The conventional system consists of a fixed Y. Arai (*) · T. Ninomiya · T. Kato · Y. Masuda Institute for Oral Science, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri, Nagano 399-0781, Japan Tel./Fax +81-263-51-2096 e-mail: arai_y@po.mdu.ac.jp A. Yamada Rigaku Mechatronics Co., Ltd., Tokyo, Japan micro-focus X-ray tube and a sensor, with a turntable be- tween them. The sample is set on the turntable during the scan. The m CT also enables observation of microscopic bone structures. When small animals are set on the turn- table, 1–4 the exposure time ranges from a few minutes to hours. In order to study morphological changes in relation to growth and aging, a long follow-up period with an indi- vidual animal is required. Kinney et al. 5 examined changes in the three-dimensional structures of trabecular bone of the tibia over a period of a month using the conventional system, but this type of study has rarely been attempted because of the difficulty inherent in leaving animals on the turntable for minutes to hours to complete the scanning. Arai and colleagues 6–11 developed a limited cone-beam X-ray CT system for dentistry in 1997. In this system, an X-ray tube and imaging intensifier (I.I.) rotate around the patient’s head. The system is characterized by a high resolu- tion (voxel size, 0.125 mm), quick operation (exposure time, 17 s), and a low effective dose (about 10 mSv/exposure.). 6–11 We report herein a newly developed m CT system that employs the method used for limited cone-beam CT in dentistry. Materials and methods Figure 1 shows an overview of the new m CT system. The micro-focus X-ray tube was used. The focus size is 7 mm (L9181S; Hamamatsu Photonics, Hamamatsu, Japan), and the X-ray sensor has a 4-inch (~10-cm) I.I. (C7336; Hamamatsu Photonics). The X-ray source and I.I. are connected by a base plate (the so-called I-arm). The I-arm rotates in a vertical plane driven by a direct-drive motor. Thus, this system is a rotate–rotate cone-beam X-ray CT system. Figure 2 illustrates schematically both the conven- tional and newly developed systems. The distance from the center of rotation to the X-ray focus ranges between 25 and 250 mm; and that from the rotation center to the I.I. surface screen from 100 to 300 mm. An object stage (10 ¥ 10 cm) is