Multimodal Biomedical Imaging Systems - Biomedical Optical Imaging Technologies: Design and Applications - page 331

high-speed MEMS mirror typically has a small mirror and it can only be used for a
small beam, possibly limiting the NA, therefore the resolution.

9.4 Multimodal Imaging System for Dental Application

The multimodal imaging system has a great potential in detecting early tooth decay
with high sensitivity and specificity. The polarized, true-color tooth image enables
dentists to examine tooth condition without specular reflection. With the help of a
polarized reflectance image, fluorescence imaging can screen the large region and
identify an abnormal region quickly. OCT imaging can then further investigate the
structural changes in the abnormal region [ 38 ].
For reflectance and fluorescence imaging, the FOV should be large enough to
cover at least one tooth so that the abnormal region can be detected quickly, and the
depth of field should be sufficient to obtain a good image of the entire tooth surface.
Therefore, the configuration in Fig. 9.7 b is a better option. Polarized reflectance
imaging and fluorescence imaging share the same imaging path. A Fourier-domain
OCT system based on a swept laser source is used for higher imaging speed and
lower noise. In order to combine the three imaging modalities with reasonable
working distance, the optical configuration in Fig. 9.11 a is advantaged for OCT
scanning. This section will discuss the detailed design of this multimodal imaging
system [ 39 ].

9.4.1 Introduction to Detection of Dental Caries

Dental caries is an infectious, communicable disease resulting in destruction of
tooth structure by acid-forming bacteria found in dental plaque, an intraoral biofilm,
in the presence of sugar. The infection results in the loss of tooth minerals that
begins with the outer surface of the tooth and can progress through the dentin to
the pulp, ultimately compromising the vitality of the tooth. The early detection
and characterization of caries lesions is very important because surgical restorative
procedures can be reduced. If detected at an early stage, the dental practitioner can
implement measures to reverse and control caries, such as identifying patients in
need of preventive care, implementing fluoride treatments, implementing plaque
control measures, and identifying patients that are at high risk of developing dental
caries.
Many optical technologies have been developed to characterize the changes of
optical properties of tooth structure related to demineralization. Those technolo-
gies include reflectance, fluorescence, transillumination [ 40 ], confocal [ 41 ], OCT