Johan Van Cleynenbreugel

Age Calculation Using X-ray Microfocus Computed Tomographical Scanning of Teeth: A Pilot Study

To correlate dental age with an individuals chronological age based on the calculated volume ratio of pulp versus tooth volume measured, an X-ray microfocus computed tomography unit (microCT) with 25 microm spatial resolution was used to non-destructively scan 43 extracted single root teeth of 25 individuals with well-known chronological age. Custom-made analysis software was used by two examiners to obtain numerical values for pulpal and tooth volume. The ratio of both was calculated and statistically processed. No significant intra- or inter-examiner differences were found. In fact, a very strong concordance correlation coefficient was found. Linear regression analysis showed a coefficient of determination (r) of 0.31 which suggests that there is a rather weak correlation between the volume ratio of pulp versus tooth and biological age. Although rather time consuming, this technique shows promising results for dental age estimation in a non-destructive manner using X-ray microfocus computed tomography.

Fast Soft Tissue Deformation with Tetrahedral Mass Spring Model for Maxillofacial Surgery Planning Systems

Maxillofacial surgery simulation and planning is an extremely challenging area of research combining medical imagery, computer graphics and mathematical modelling. In maxillofacial surgery abnormalities of the skeleton of the head are treat by skull remodelling. Since the human face plays a key role in interpersonal relationships, people are very sensitive to changes to their outlook. Therefore planning of the operation and reliable prediction of the facial changes are very important. Recently, the use of 3D image-based surgery planning systems is more and more accepted in this field. Although the bone-related planning concepts and methods are maturing, prediction of soft tissue deformation needs further fundamental research. In this paper we present a soft tissue simulator that uses a fast tetrahedral mass spring system to calculate soft tissue deformation due to bone displacement in a short time interval. Results of soft tissue simulation for patients who had a maxillofacial surgery are shown. Finally we truly validated the simulation results and compared our method with others.

Computer Aided Diagnosis for CT Colonography via Slope Density Functions

The paper presents a system for Computer Aided Detection in Virtual Colonography based on geometric modeling. We label locations in the CT volume data, which have a high probability of being colonic polyps, and present them in a user-friendly way. We introduce a method for fast colonic wall elimination and then model polyps based on Slope Density Functions, to be able to reduce the number of false positive cases. The method was tested on a study group of 50 data sets. Using normal colonoscopy as standard of reference, true positive and false positive findings were determined. The detection rate for polyps larger than 6mm was above 85%. Initial results show that Computer Aided Diagnosis is feasible and that our method holds potential for screening purposes.

A System to Support Laparoscopic Surgery by Augmented Reality Visualization

This paper describes the development of an augmented reality system for intra-operative laparoscopic surgery support.The goal of this system is to reveal structures, otherwise hidden within the laparoscope view. To allow flexible movement of the laparoscope we use optical tracking to track both patient and laparoscope.The necessary calibration and registration procedures were developed and bundled where possible in order to facilitate integration in a current laparoscopic procedure. Care was taken to achieve high accuracy by including radial distortion components without compromising real time speed.Finally a visual error assessment is performed, the usefulness is demonstrated within a test setup and some preliminary quantitative evaluation is done.

Computer aided detection for low-dose CT colonography

The paper describes a method for automatic detection of colonic polyps, robust enough to be directly applied to low-dose CT colonographic datasets. Polyps are modeled using gray level intensity profiles and extended Gaussian images. Spherical harmonic decompositions ensure an easy comparison between a polyp candidate and a set of polypoid models, found in a previously built database. The detection sensitivity and specificity values are evaluated at different dose levels. Starting from the original raw-data (acquired at 55mAs), 5 patient datasets (prone and supine scans) are reconstructed at different dose levels (down to 5mAs), using different kernel filters and slice increments. Although the image quality decreases when lowering the acquisition mAs, all polyps above 6mm are successfully detected even at 15 mAs. Accordingly the effective dose can be reduced from 4.93mSv to 1.61 mSv, without affecting detection capabilities, particularly important when thinking of population screening.

Computer Aided Diagnosis for Virtual Colonography

The success of CT colonography (CTC) depends on appropriate tools for quick and accurate diagnostic reading. Current advancements in computer technology have the potential to bring such tools even to the PC level. In this paper a technique for Computed Aided Diagnosis (CAD) using CT colonography is described. The method labels positions in the volume data, which have a strong likelihood of being polyps and presents them in a user-friendly way. This method will reduce the amount of time needed by the radiologist to make a correct diagnosis. The method was tested on a study group of 18 patients and the sensitivity for polyps of 10 mm or larger was 100%, comparable to that of human readers. The price paid for a high detection rate was a large number of approximately 8 false positive findings per case.

A Simulation Environment for Maxillofacial Surgery Including Soft Tissue Implications

This paper describes work in progress in the area of planning and prediction of maxillofacial surgery. We focus on true 3D problems which cannot be addressed by conventional 2D cephalometric radiographs. Examples are bilateral repositioning of the zygoma’s or treating facial asymmetries. The environment being developed arose from the need of patients for prediction of their expected post-op outlook and from the need of surgeons for better support to reach the desired result. Our simulation environment adheres to a scene-based approach in which CT image-derived visualizations and additional 3D photographs (showing the face surface and its natural complexion) are co-presented and manipulated. Tools for non-planar osteotomy are included. Repositioning of bone fragments is made possible. Furthermore, a voxel displacement formalism is presented to account for soft tissue implications. Combining these simulation tools, a qualitative prediction of the facial outlook is obtained. Results are shown for a case of hypoplastic zygoma repositioning.

Spiral Computed Tomography Based Maxillary Sinus Imaging in Relation to Tooth Loss, Implant Placement and Potential Grafting Procedure

ABSTRACT Objectives The purpose of the present study was to explore the maxillary sinus anatomy, its variations and volume in patients with a need for maxillary implant placement. Material and Methods Maxillary sinus data of 101 consecutive patients who underwent spiral computed tomography (CT) scans for preoperative implant planning in the maxilla at the Department of Periodontology, University Hospital, Catholic University of Leuven, Leuven, Belgium were retrospectively evaluated. The alveolar bone height was measured on serial cross-sectional images between alveolar crest and sinus floor, parallel to the tooth axis. In order to describe the size of the maxillary sinus anteroposterior (AP) and mediolateral (ML) diameters of the sinus were measured. Results The results indicated that the alveolar bone height was significantly higher in the premolar regions in comparison to the molar region (n = 46, P < 0.01). The age showed negative relation to bone dimension (r = - 0.32, P = 0.04). Anterior and posterior border of the maxillary sinuses were mostly located in the first premolar (49%) and second molar (84%) regions, respectively. Maxillary sinus septa were indentified in 47% of the maxillary antra. Almost 2/3 (66%) of the patients showed major (> 4 mm) mucosal thickening mostly at the level of the sinus floor. The present sample did not allow revealing any significant difference (P > 0.05) in maxillary sinus dimensions for partially dentate and edentulous subjects. Conclusions Cross-sectional imaging can be used in order to obtain more accurate information on the morphology, variation, and the amount of maxillary bone adjacent to the maxillary sinus.

Registration of 3D Photographs with Spiral CT Images for Soft Tissue Simulation in Maxillofacial Surgery

Prediction of the facial outcome after maxillofacial surgery is not only of major interest for surgeons but also for patients. A mirrorlike image of the expected surgical outcome gives important information for the patient and provides the surgeon with a good communication tool. This paper presents a method for registration of 3D photographs with 3D CT images, to provide the patient with a realistic view of the natural complexion of the simulated postoperative outcome of his/her face. A rigid ICP-based registration algorithm, followed by a non-rigid transformation produces a close match between the two surfaces.

A Flexible Environment for Image Guided Virtual Surgery Planning

We present an object-oriented environment built on top of OpenGL and intended for virtual planning of image-guided surgery. We enumerate typical requirements from this field and show how they are coped with by our developments. A number of already derived surgery planning applications demonstrates the flexibility of our environment.