Multimodal Biomedical Imaging Systems - Biomedical Optical Imaging Technologies: Design and Applications - page 334

a b

505 Different tooth regions

No caries (1)
Initial caries (2)
Advanced caries (3)

5000

4000

466

582 3000

540

632

2000

1000

0

400 500 600 700 800

400 500 600

Wavelength / nm

Wavelength / nm

Fig. 9.12 ( a ) Fluorescence excitation spectrum of a strong fluorescent carious region. Fluores-
cence was detected at 700 nm. ( b ) Emission spectra at different region with excitation wavelength
of 400 nm [ 53 ]

180
160

140
120
100

Water

80
60
40

enamel

20
0

600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Wavelength (nm)

Fig. 9.13 The attenuation coefficient of dental enamel [ 54 ]

shown in Fig. 9.13 , the magnitude of scattering decreases exponentially at longer
wavelengths and reaches minimum around 1,300 nm [ 54 ]. At longer wavelengths
past 1,550 nm, the attenuation coefficient is not expected to decrease further due to
the increasing absorption coefficient of water which is 12 % by volume in dental
enamel. Therefore, a swept-source laser with a central wavelength of 1,325 nm and
a bandwidth of 100 nm is used in this multimodal imaging system.

9.4.3 Detector

Because it is an area imaging system, an area detector, namely, CCD or CMOS, is
needed. Ideally, a cooled CCD is the best choice for fluorescence imaging because