published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Mathematics / Doctoral / Doctor of Philosophy

Data on the three?dimensional (3?D) morphology of normal faces and facial deformities as well as objective techniques for evaluating postoperative changes are currently unavailable. With the advent of stereophotography and cone?beam CT (CBCT), it is possible to acquire 3?D images of soft and hard tissues of the maxillofacial complex. A series of studies were conducted aimed at 1) establishing 3?D facial anthropometric norms for Hong Kong young adults, 2) determining 3?D facial anthropometric features in skeletal Class II and III deformities, 3) characterizing the oropharyngeal space in Class II and III skeletal deformities, 4) exploring clinical applications of 3?D colour maps, 5) establishing a non?invasive technique for estimating serial volume changes and 6) creating virtual craniofacial models by fusing 3?D photographs and CBCT images. Study 1: A stereophotographic system was used to capture 3?D images of 103 Hong Kong Chinese young adults with normal balanced faces. An anthropometric analysis protocol with linear, angular and proportional measurements was developed to establish a normative database and quantify dysmorphology. The Hong Kong Chinese norms were distinct from Caucasians, especially with regard to ocular and nasal measurements. Facial height and nasolabial measurements differed significantly between Hong Kong males and females. Study 2: Anthropometric analyses of 3?D facial images from 41 skeletal Class II and 43 Class III subjects were performed. The Class II subjects had increased lower facial height compared with Class III, who had longer total facial heights and narrower faces. While Class II deformity primarily resulted from mandibular deficiency with a normal maxilla, Class III presented as combined midfacial hypoplasia and mandibular hyperplasia. Study 3: Anthropometric characteristics of the oropharygeal space in skeletal Class II and III were evaluated using 62 CBCT scans. The retroglossal (RG) and retropalatal (RP) volumes and average cross sectional areas were significantly larger in Class III than Class II skeletal deformity. The RP compartment was larger but less uniform than the RG compartment in both Classes. Study 4: 3?D photographs or CBCT images acquired at two different time points were superimposed using a common unaffected area. 3?D colour maps were generated depicting distance differences between superimposed images in a graphical format. These maps were used as an objective tool for treatment planning and assessing outcomes after orthognathic surgery, bimaxillary distraction and facial trauma. Study 5: 3?D photogrammetry was employed for planning soft tissue expansion (STE) and transplantation of a vascularised scapular flap in hemifacial microsomia. This technique facilitated the identification of extent and degree of tissue deficiency, selection of the appropriate tissue expander, monitoring volumetric changes during STE and estimation of the free flap dimensions. Study 6: 3?D facial photographs and CBCT scans of 29 subjects were merged to create virtual craniofacial models with natural surface texture. Accuracy was assessed with 3?D colour maps and Root Mean Square (RMS) error. The CBCT and 3?D photographic data were integrated while minimizing average RMS error to 0.441mm. These virtual composite craniofacial models permitted concurrent 3?D assessment of bone and soft tissue. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

We derive the expression for the three-dimensional incoherent optical transfer function when third-order spherical aberration is present. The normalized version of the transfer function is numerically calculated for various amounts of spherical aberration. We find the effects of the aberration to be highly dependent on the spatial frequency in the longitudinal direction. We also calculate a structure content parameter, as a quality criterion, from the normalized transfer function. Remarkably, the structure content parameter dependence on spherical aberration is well-fit by a simple Cauchy curve for aberrations out to two waves at the margin.

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No description available.