LASER TOMOGRAPHY OF EXTRACTED HUMAN TEETH USING COHERENT DETECTION IMAGING

• Project/Area Number: 10357017
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 展開研究
• Research Field: Conservative dentistry
• Research Institution: TOHOKU UNIVERSITY
• Principal Investigator: HORIUCHI Hiroshi DENTISTRY, TOHOKU UNIVERSITY, PROFESSOR, 歯学部, 教授 (00013962)
• Co-Investigator(Kenkyū-buntansha): ISHIHATA Hiroshi DENTISTRY, TOHOKU UNIVERSITY, RESEARCH FELLOWSHIP, 歯学部・附属病院, 助手 (40261523) ; IIYAMA Masao DENTISTRY, TOHOKU UNIVERSITY, RESEARCH FELLOWSHIP, 歯学部, 助手 (00193152) ; ENDO Hideaki DENTISTRY, TOHOKU UNIVERSITY, RESEARCH FELLOWSHIP, 歯学部, 助手 (80168830) ; INABA Humio TOHOKU INST. OF TECH., PROFESSOR, 教授 (90006213) ; SHOJI Kanako DENTISTRY, TOHOKU UNIVERSITY, RESEARCH FELLOWSHIP, 歯学部・附属病院, 助手 (90302158)
• Project Period (FY): 1998 – 1999
• Project Status: Completed (Fiscal Year 1999)
• Budget Amount: ¥27,500,000 (Direct Cost: ¥27,500,000); Fiscal Year 1999: ¥3,900,000 (Direct Cost: ¥3,900,000); Fiscal Year 1998: ¥23,600,000 (Direct Cost: ¥23,600,000)
• Keywords: LASER / COMPUTOR TOMOGRAPHY / HETERODYNE / TOOTH

Research Abstract

Optical sensing methods for the functional monitoring of biological tissues are recently receiving widespread attention. One of the emerging application of optical methods is its potential use in imaging. Light being non-ionizing nature, is relatively safe has capabilities for the non-invasive and non-destructive monitoring of the structural and functional states of patients. One of the proposed technique for spectroscopic optical imaging of biological tissues is referred to as the coherent detection imaging (CDI) method that is based on optical heterodyne detection [1,2]. The CDI method possesses high sensitivity and directional selectivity in detecting the coherence retaining and the least scattering photons from tissues. In this study, we used this measurement system to obtain optical tomographic images of extracted human teeth with submillimeter resolution.
Ten human extracted teeth were used in this study. Continuous wave, single frequency, semiconductor laser (532nm) were used as the light sources. The output of the laser was split into signal and reference beams. They were frequency shifted by a pair of acousto-optic modulators to 80 MHz and 100 MHz, respectively. The diameter of the incident beam was 200μm. The transmitted beam from opposite side of the tooth was superposed on the reference beam and impinged on a photodiode generating an intermediate frequency at 20MHz. The measurement system has a dynamic range of 〜90dB. The tooth was mounted on a translational-rotational (T-R) stepper and the scanning was performed in the T-R mode similar to that of the conventional computed tomography. Approximately 20 min was required for each image acquisition. The image reconstruction was done using the filtered back projection (FBP). After the optical measurement, thin sections (500μm thickness, approx.) of the root, at the measurement plane were made. Laser CT images of teeth were compared to the microscopic cross sections and assessed. The internal structure of teeth, pulp cavities and canals were reflected in the horizontal images, and also the site of the transparent dentine could be located.
Dentine is a highly scattering tissue, and the incident light is heavily dispersed and attenuated. It seems to be difficult that such as X-ray imaging. We had earlier demonstrated that the CDI has the capability to selectively detect the least forward scattered light transmitted from dentine slabs (J Dent Res 74 : IADR abstract 423, 1995). This component of the emergent light was used to reconstruct the tomographic images in the present study. Our results indicate that the CT images obtained by CDI is reliable to detect the internal structure of the tooth. Relative low light attenuation is observed in the pulp cavity, canals and transparent dentine. The light sources with other shorter wavelengths could provide more information on the monitoring of teeth functions such as the circulation in the pulp. The CDI method has an advantage as a remote detection method. There is a possibility to arrange detectors outside of the oral cavity. The CDI method is reliable to visualize the internal structure of the tooth. This method may also be applicable to the detection of the circulation in the pulp.