Development of Time-domain Full-field Optical Coherence Tomography as a Non-destructive Testing Method


Zhang, Jinke (2017) Development of Time-domain Full-field Optical Coherence Tomography as a Non-destructive Testing Method. PhD thesis, University of Liverpool.

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Abstract

Optical coherence tomography (OCT) serves as a non-destructive and non-invasive technique that is capable of imaging the inner structure of optical scattering samples with a high spatial resolution and deep penetration depth. Full-field time-domain OCT (FF-TD-OCT) is an extension of time-domain OCT (TD-OCT) which uses a two-dimensional (2D) detector to capture a series of en-face images to reconstruct the inner structure of samples in three-dimension (3D). In pharmaceutical industry, the pellet or tablet coating performs an important role in the release of active pharmaceutical ingredients (API) and controlling the desired API absorption rate in human body. Therefore, the accurate evaluation of coating thickness is vital to the pharmaceutical coating process. Our FF-TD-OCT system was developed in this research to image the pharmaceutical coating of small size pellets with a high axial resolution of 3.9μm and lateral resolution of 4.4μm. We characterized two pellet samples: a two-layer pellet with one clear coating layer and one drug-loaded layer, and a three-layer pellet with one clear coating layer and two drug-load layers. The mean thickness of a two-layer pellet was precisely determined automatically as 39.7±7.3μm and 49.1±7.0μm for the outer and inner layers respectively. The mean thickness of a three-layer pellet were 26.5±2.3μm, 20.6±3.4μm and 57.3±7.2μm respectively. In addition, the particles in the drug-loaded layer can be clearly resolved form the cross-section image. The precise and power information of the human corneal surface is of significant benefit in corneal corrective surgeries. Our developed FF-TD-OCT was combined with an average back-vertex focal length and average powercalculation algorithm in order to measure and calculate the individual power of the corneal surface. Meanwhile, the angle of incident light was considered as an important parameter and the errors introduced by the paraxial approximation was reduced. We managed to measure six formalin-fixed and two fresh corneas and map the surface power information of them. In addition, the cross-section image of cornea generated from our FF-TD-OCT system showed its structure including epithelium, Bowman’s layer and stroma clearly and the features of the stroma. For automotive paint system, the metallic flakes in base coat has a significant effect on the appearance of automotive bodies. Precise evaluation of the properties of these flakes is important in the automotive painting system in the purpose for quality assurance. Our FF-TD-OCT system was combined with a 3D variational segmentation method to measure and segment the individual flakes within the base coat of automotive paint system in 3D for the first time. The properties of flakes, including number, size and orientation in 3D space, were precisely calculated, which cannot be achieved by current commercial methods.

Item Type: Thesis (PhD)
Divisions: Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User: Symplectic Admin
Date Deposited: 14 Aug 2018 07:59
Last Modified: 01 Aug 2023 01:30
DOI: 10.17638/03015759
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3015759
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