Multi-resolution dental image registration based on genetic algorithm

The Automated Dental Identification System (ADIS) is a Post Mortem Dental Identification System. This thesis presents dental image registration, required for the preprocessing steps of the image comparison component of ADIS. We proposed a multi resolution dental image registration based on genetic algorithms. The main objective of this research is to develop techniques for registration of extracted subject regions of interest with corresponding reference regions of interest.;We investigated and implemented registration using two multi resolution techniques namely image sub sampling and wavelet decomposition. Multi resolution techniques help in the reduction of search data since initial registration is carried at lower levels and results are updated as the levels of resolutions increase. We adopted edges as image features that needed to be aligned. Affine transformations were selected to transform the subject dental region of interest to achieve better alignment with the reference region of interest. These transformations are known to capture complex image distortions. The similarity between subject and reference image has been computed using Oriented Hausdorff Similarity measure that is robust to severe noise and image degradations. A genetic algorithm was adopted to search for the best transformation parameters that give maximum similarity score.;Testing results show that the developed registration algorithm yielded reasonable results in accuracy for dental test cases that contained slight misalignments. The relative percentage errors between the known and estimated transformation parameters were less than 20% with a termination criterion of a ten minute time limit. Further research is needed for dental cases that contain high degree of misalignment, noise and distortions

Computer aided detection of natural reference markers in serial radiographs of growing bone

This thesis describes the theoretical and experimental development and testing of a computer-based image processing system for the detection of stable structural features in serial radiographs of growing bone. The study is divided into three parts. First, a simple theoretical model for the detection of stable structures in a radiographic sequence was developed together with a more detailed statistical model of the processes which hinder detection. Analysis of the models indicated that the processing procedures needed to perform the detection were those described by the so-called "matched filter equation". Secondly, the assumptions of the model were tested in a series of experiments using serial radiographs of 24 children with implanted tantalum markers, drawn from the files of the University of Washington, USA. Information gained from these experiments prompted changes to the detection method to allow the radiographic data to comply with these assumptions and provide robustness against image noise. The method was implemented as a semi-automatic image processing system on a Sun 3/160 computer. The system was tested in a further series of experiments using a second sample of radiographs of 28 children with implanted markers and with radiographs of dried human skulls. The results of these experiments indicated that the system could detect persistent structural features whose positions were consistent with the stable tantalum markers and that the system was robust against minor changes in projection between radiographs. Finally, the detection system was applied to the investigation of mandibular incisor eruption from intra-alveolar to pubertal eruption stages using serial lateral cephalometric radiographs of 11 children. This investigation revealed two new features of incisor eruption: first, the eruption paths deviated lingually at, or just prior to, alveolar emergence; and second, post-emergence eruption was characterised by a labio-lingual oscillation of the crowns of the incisors

A pilot study for the digital replacement of a distorted dentition acquired by Cone Beam Computed Tomography (CBCT)

Abstract Introduction: Cone beam CT (CBCT) is becoming a routine imaging modality designed for the maxillofacial region. Imaging patients with intra-oral metallic objects cause streak artefacts. Artefacts impair any virtual model by obliterating the teeth. This is a major obstacle for occlusal registration and the fabrication of orthognathic wafers to guide the surgical correction of dentofacial deformities. Aims and Objectives: To develop a method of replacing the inaccurate CBCT images of the dentition with an accurate representation and test the feasibility of the technique in the clinical environment. Materials and Method: Impressions of the teeth are acquired and acrylic baseplates constructed on dental casts incorporating radiopaque registration markers. The appliances are fitted and a preoperative CBCT is performed. Impressions are taken of the dentition with the devices in situ and subsequent dental models produced. The models are scanned to produce a virtual model. Both images of the patient and the model are imported into a virtual reality software program and aligned on the virtual markers. This allows the alignment of the dentition without relying on the teeth for superimposition. The occlusal surfaces of the dentition can be replaced with the occlusal image of the model. Results: The absolute mean distance of the mesh between the markers in the skulls was in the region of 0.09mm ± 0.03mm; the replacement dentition had an absolute mean distance of about 0.24mm ± 0.09mm. In patients the absolute mean distance between markers increased to 0.14mm ± 0.03mm. It was not possible to establish the discrepancies in the patient’s dentition, since the original image of the dentition is inherently inaccurate. Conclusion: It is possible to replace the CBCT virtual dentition of cadaveric skulls with an accurate representation to create a composite skull. The feasibility study was successful in the clinical arena. This could be a significant advancement in the accuracy of surgical prediction planning, with the ultimate goal of fabrication of a physical orthognathic wafer using reverse engineering

Dental Biometrics: Human Identification Using Dental Radiograph

Biometric is the science and innovation of measuring and analyzing biological information.In information technology, biometric refers to advancements that measures and analyzes human body attributes,for example,DNA, eye retinas, fingerprints and irises,face pattern,voice patterns,and hand geometry estimations,for identification purposes.The primary motivation behind scientific dentistry is to distinguish expired people,for whom different method for recognizable proof(e.g.,unique finger impression,face,and so on.)are not accessible.Dental elements survives most of the PM events which may disrupt or change other body tissues,e.g. casualties of motor vehicles mishaps,fierce violations,and work place accident,whose bodies could be deformed to such a degree,that identification even by a family member is neither desirable nor reliable.Dental Biometric utilises dental radiographs to distinguish casualties.The radiographs procured after the casualty's demise are called post-mortem radiograph and the radiograph obtained when the casualty was alive is called ante-mortem radiograph.The objective of dental biometric is to match the unidentified individual's post-mortem radiograph against a database of labelled antemortem radiograph.This thesis proposes a novel method for the contour extraction from dental radiographs.The proposed algorithm of Active Contour Model or the Snake model is used for this purpose. A correctly detected contour is essential for proper feature extraction.This thesis only works on the contour detection.The method has been tested on some radiographs images and is found to produce desired output.However,the input radiograph image may be of low quality,may suffer a clear separation between two adjacent teeth.In that case the method will not be able to produce a satisfactory result.There is a need of pre-processing(e.g. contrast enhancement) before the active contour detection model can be applie

Assessment of 3D Facial Scan Integration in 3D Digital Workflow Using Radiographic Markers and Iterative Closest Point Algorithm

Introduction: Integration of 3 dimensional (3D) facial scanning into digital smile design workflows has been made available in multiple commercially available systems. Limited data exists on the accuracy of facial scans and accuracy of various methods of merging facial scans with cone beam computed tomography (CBCT) scans.Objective: The purpose of this prospective clinical study was to evaluate the accuracy of 2 methods used to integrate soft tissue facial scans with CBCT scans. It would allow proposal of a novel approach for integrating a 3D facial scan using facial radio-opaque markers in a 3D digital workflow.Material and methods: Fifteen CBCT and 3D face scans were obtained from patients who were undergoing treatment at MUSoD. A DICOM with RO markers and 3 STL data files from the facial scans were obtained for each patient. These files were superimposed using Exocad software. Accuracy of superimpositions was evaluated by measuring distances between RO markers on DICOM and STL data. The obtained dataset was analyzed using the paired t-test. Results: The results showed that the mean values for the 6 subsets, merging through the ICP algorithm, were 1.47-2mm. However, when merged by RO markers, the mean valuewas 0.14mm. Using a paired t-test, the novel RO points method was statistically more accurate than ICP algorithm method (

Comparative linear accuracy of cone beam CT derived 3D images in orthodontic analysis.

Objective . To compare the in vitro reliability and accuracy of linear measurements between cephalometric landmarks on CBCT 3D images with varying basis projection images to direct measurements on human skulls. Methods . Sixteen linear dimensions between anatomical sites marked on 19 human skulls were directly measured. Skulls were imaged with CBCT at three settings: 153, 306, and 612 basis projections. The mean absolute error and modality mean of linear measurements between landmarks on 3D images were compared to the anatomic truth. Results . No difference in mean absolute error between the scan settings was found. The average skull absolute error between marked reference points were less than the distances between unmarked reference sites. Conclusion . CBCT measurements were consistent between scan sequences and for direct measurements between marked reference points. Reducing the number of projections for 3D reconstruction did not lead to reduced dimensional accuracy and potentially provides reduced patient radiation exposure

Comparative linear accuracy and reliability of cone beam CT derived 2-dimensional and 3-dimensional images constructed using an orthodontic volumetric rendering program.

The purpose of this project was to compare the accuracy and reliability of linear measurements made on 2D projections and 3D reconstructions using Dolphin 3D software (Chatsworth, CA) as compared to direct measurements made on human skulls. The linear dimensions between 6 bilateral and 8 mid-sagittal anatomical landmarks on 23 dentate dry human skulls were measured three times by multiple observers using a digital caliper to provide twenty orthodontic linear measurements. The skulls were stabilized and imaged via PSP digital cephalometry as well as CBCT. The PSP cephalograms were imported into Dolphin (Chatsworth, CA, USA) and the 3D volumetric data set was imported into Dolphin 3D (Version 2.3, Chatsworth, CA, USA). Using Dolphin 3D, planar cephalograms as well as 3D volumetric surface reconstructions were (3D CBCT) generated. The linear measurements between landmarks of each three modalities were then computed by a single observer three times. For 2D measurements, a one way ANOVA for each measurement dimension was calculated as well as a post hoc Scheffe multiple comparison test with the anatomic distance as the control group. 3D measurements were compared to anatomic truth using Student\u27s t test (PiÜ50.05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were determined as indices of intraobserver reliability. Our results show that for 2D mid sagittal measurements that Simulated LC images are accurate and similar to those from PSP images (except for Ba-Na), and for bilateral measurements simulated LC measurements were similar to PSP but less accurate, underestimating dimensions by between 4.7% to 17%.For 3D volumetric renderings, 2/3 rd of CBCT measurements are statistically different from actual measurements, however this possibly is not clinically relevant

A three dimensional analysis of soft tissue and bone changes following orthognathic surgery

Introduction: This report investigates the ability of surgeons to achieve predicted surgical movements in five different groups of patients, and analyses both the predictions and the changes in two dimensions using scale space analyses (Campos 1991). The report then progresses to the three dimensional analysis of the bone, the soft tissues and the ratio of soft tissue to bone following surgery, using a colour coded techniques (Fright and Linney, 1991) to illustrate the changes. The average soft tissue scans from each group of patients were averaged and compared to a control group at the preoperative, three months and 1 year postoperative stages (Fright, 1991) Data Acquisition: Bone measurements were recorded from lateral skull radiographs preoperatively and 48 hrs postoperatively, and CT scans preoperatively and 1 year postoperatively. Soft tissue measurements from an optical scanner, preoperatively, three months and 1 year postoperatively. Patients 1) Control group: 30 females and 30 males 2) Skeletal class 2 patients: 15 Females and 2 Males 3) Skeletal class 3 patients: 9 Females and 7 Males 4) Cleft Palate Patients a) Unilateral cleft lip and palate: I 6 Females: 2 left and 4 right sided clefts 7 Males: 3 left and 4 right sided clefts b) Bilateral cleft lip and palate: 5 Males and 1 Female c) Clefts of the Hard and Soft palate: 5 Females. Results: Prediction: There was a surprisingly poor match between the predicted and achieved movements in both the horizontal and vertical direction in all patient groups. The scale space analysis provided an efficient method of illustrating profile changes. Soft tissue movements There were definite patterns of change and relapse in the patient groups. The relapse being most marked in the cleft palate patients. Bone movements and soft tissue to bone ratios Definite patterns of movement for the maxilla and the mandible became apparent for both the bone and soft tissue to bone ratio of movement in each group. For maxillary impactions in the skeletal 2 group there was a 1:1 ratio of movement of the soft tissue to bone in the midline increasing to 1.25:1 in the canine region and 1.5:1 in the paranasal region. Conclusions: There is a need to develop a technique to aid the the surgeons in carrying out planned surgical movements. The colour coded method was shown to be a simple, efficient and easily understandable way of analysing surgical change. Diagnosis of surgical requirements was aided by the ability to objectively compare the individual to a control group. The prediction of surgical change should be greatly aided by adapting the current database to include the distinct patterns of movement in the bone and ratio of movements of the soft tissues to the bone