Several studies have demonstrated the potential of short wavelength infrared (SWIR) reflectance, thermal imaging and optical coherence tomography for the nondestructive assessment of the activity of caries lesions. The purpose of this study was to test the hypothesis that the activity of arrested caries lesions on the coronal surfaces of extracted teeth would be changed by reducing the thickness of the highly mineralized transparent surface layer, which was measured using polarization sensitive optical coherence tomography (PS-OCT). The lesion activity was assessed using SWIR reflectance and thermal imaging during forced air drying of the lesion before and after mechanical removal of a surface layer ~ 50-μm thick covering the lesion. Both the intensity change in SWIR reflectance images at 1500- 1750-nm wavelengths after drying the lesions and the change in thermal emission measured with a thermal camera at 8-13-μm wavelengths increased significantly (P<0.05) after reducing the thickness of the mineralized surface layer in the lesions indicating the permeability of the lesion to fluids increased. These results provide further evidence that the presence of a highly mineralized outer surface layer is a key indicator of lesion arrest.
An algorithm is presented that can be used to obtain accurate optic axis orientation of birefringent tissue samples. A single-mode fiber (SMF)-based polarization-sensitive optical coherence tomography with a single linearly polarized incident light was used in the measurements in which the light reflected from the sample and detected by the spectrometer is linearly polarized light at 45 deg with respect to the experimental horizontal axis. By employing polarization controllers to completely specify the parameters of the fiber system, the absolute optic axis orientation could then be estimated accurately by analyzing the Mueller matrices of the fiber system and sample. The proposed algorithm has been validated in the quantification of the optic axis orientation of a quarter-wave plate. Finally, several birefringent tissue samples were imaged with this SMF-based system.
The polarization-sensitive spectral domain optical coherence tomography (PSOCT) has the advantages of being able to
measure the polarization properties of samples, such as phase-retardation, diattenuation, depolarization, and optical axis
orientation, providing a contrast to identify the diseased area and normal area in tissues in PSOCT images.
Conventionally, the sample arm of PSOCT is fixed on the stage where biomedical tissues or models is placed, and the
OCT images is acquired by scanning with a galvanometer-based mirror. To be applied in the practical diagnosis, a
promising way is to design a hand-held device. To this end, it is required that probe is assembled with a small volume to
allow for comprehensively imaging large tissues areas at a microscopic scale, and is available to move on different
samples to be acquired quickly with negligible motion artifacts. Meanwhile, the probe should be manufactured wih well
stability to avoid system jitter error while it is used to detect the biological tissues in vivo. In this work, a design of a
hand-hold fiber-based PSOCT is described. The device is of the size of 10 cm (length) × 8 cm (width) × 6 cm (height).
Both the axial resolution and the imaging depth of the system are measured and were approximately 7 μm and 2.5 mm in
air, respectively, which are in good agreement with the theoretical predictions. The A-scan rate of the system is 70 kHz.
The structure is compact and all the components are fixed on the shell to reduce the motion artifact, resulting in a great
stability on measuring the tissues in vivo. The cross sectional images of ex vivo chicken breast, ex vivo pork cartilage
and in vivo forearm skin of human wolunteer are presented to demonstrate the capability of the system.
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