Metal artifact reduction in dental CT images using polar mathematical morphology

Most dental implant planning systems use a 3D representation of the CT scan of the patient under study as it provides a more intuitive view of the human jaw. The presence of metallic objects in human jaws, such as amalgam or gold fillings, provokes several artifacts like streaking and beam hardening which makes the reconstruction process difficult. In order to reduce these artifacts, several methods have been proposed using the raw data, directly obtained from the tomographs, in different ways. However, in DICOM-based applications this information is not available, and thus the need of a new method that handles this task in the DICOM domain. The presented method performs a morphological filtering in the polar domain yielding output images less affected by artifacts (even in cases of multiple metallic objects) without causing significant smoothing of the anatomic structures, which allows a great improvement in the 3D reconstruction. The algorithm has been automated and compared to other image denoising methods with successful results. (C) 2010 Elsevier Ireland Ltd. All rights reserved.This work has been supported by the project MIRACLE (DPI2007-66782-C03-01-AR07) of Spanish Ministerio de Educacion y Ciencia.Naranjo Ornedo, V.; Llorens Rodríguez, R.; Alcañiz Raya, ML.; López-Mir, F. (2011). Metal artifact reduction in dental CT images using polar mathematical morphology. Computer Methods and Programs in Biomedicine. 102(1):64-74. https://doi.org/10.1016/j.cmpb.2010.11.009S6474102

Evaluation of beam hardening artifacts around dental implants: CT study on bovine ribs

Background/Aim: The aim of this study was to evaluate beam hardening artifacts generated by Grade 4 and Grade 5 dental implants on computed tomography (CT) images at low and high kilovoltage peaks (kVp). Material and Methods: A total of 16 implants, 8 of which were Grade 4 and 8 were Grade 5, were inserted into bovine ribs. CT images of bovine ribs were acquired using two different exposure protocol: low kVp and high kVp. Beam hardening artifacts generated by Grade 4 and Grade 5 dental implants were calculated by the mean Hounsfield unit (HU) within a standardized region-of-interest (ROI). Results: Artifact in Grade 4 implants were greater than that in Grade 5 implants. Also, artifacts at the high kVp were lower than that at the low kVp. Conclusions: CT scans providing HU values can be used to evaluate the beam hardening artifact. Beam hardening artifacts decreased in the CT images with high kVp. Grade 5 dental implants have an advantage by producing less severe beam hardening artifacts

Desarrollo de un Módulo de Tratamiento de Imagen para Sistemas de Imagen Dental

Este trabajo resume los desarrollos llevados a cabo sobre reducción de artefactos metálicos y de segmentación de tejidos mandibulares que salen al paso de las limitaciones de los sistemas de imagen dental actuales. Los métodos propuestos han sido evaluados analíticamente obteniendo resultados satisfactorios respecto al estado del arte actual, hecho que ha dado lugar a un número considerable de publicaciones científicas.Lloréns Rodríguez, R. (2011). Desarrollo de un Módulo de Tratamiento de Imagen para Sistemas de Imagen Dental. http://hdl.handle.net/10251/28047.Archivo delegad

Metal Artifact Reduction in Sinograms of Dental Computed Tomography

Use of metal objects such as dental implants, fillings, crowns, screws, nails, prosthesis and plates have increased in dentistry over the past 20 years, which raised a need for new methods for reducing the metal artifacts in medical images. Although there are several algorithms for metal artifact reduction, none of these algorithms are efficient enough to recover the original image free of all artifacts. This thesis presents two approaches for reducing metal artifacts through accurate segmentation of metal objects on dental computed tomography images. First approach was based on construction and tilting of a 3D jaw phantom, aiming to obtain fewer metals on each slice. 3D jaw phantom included the main anatomical structures of a jaw, and multiple metal fillings inserted on the teeth. Each jaw slice on the 3D phantom was tilted in order to mimic the (1) nodding movement, and (2) mouth opening/closing. Second approach was to segment the metals on an experimental dataset, consisting of a Cone-Beam Computed Tomography image, by using different segmentation algorithms. K-means clustering, Otsu’s thresholding method and logarithmic enhancement were used for extracting the metals from a real dental CT slice. Once the metal fillings on the jaw phantom were segmented out from the image, they were compensated by gap filling methods; Discrete Cosine Domain Gap Filling and inpainting. Qualitative and quantitative analyses were carried out for evaluating the performance of implemented segmentation methods. Efficiency of tilting alternatives on the segmentation of metal fillings was compared. In conclusion, jaw opening/closing movement between 24º-30º suggested a significant enhancement in segmentation, thus, metal artifact reduction on the jaw phantom. Inpainting method showed a better performance for both simulated and experimental dataset over the DCT domain gap filling method. Moreover, merging the logarithmic enhancement and inpainting showed superior results over other metal artifact reduction alternatives

Rechnergestützte Planung und Rekonstruktion für individuelle Langzeit-Knochenimplantate am Beispiel des Unterkiefers

Die vorliegende Arbeit befasst sich mit der Entwicklung und Umsetzung von Methoden und Werkzeugen zur Bereitstellung von Modellen und Randbedingungen für die Konstruktion individueller Langzeit-Knochenimplantate (Konstruktionsvorbereitung). Grundlage dabei ist, dass die Planung aus medizinischer Sicht z.B. durch einen Chirurgen und die Konstruktion unter technischen Aspekten z.B. durch einen Konstrukteur getrennt erfolgt. Hierfür wird ein erarbeitetes Planungskonzept vorgestellt, welches sowohl die geplanten geometrischen Merkmale, als auch weiterführende Metadaten beinhaltet (Randbedingungen). Die Übergabe dieser Planungsdaten an die Konstruktion erfolgt über eine dafür entworfene Formatbeschreibung im Kontext der Schnittstelle zwischen Mediziner und Ingenieur. Weiterführend wird die Notwendigkeit von speziellen Funktionen für die Konstruktion von individuellen Implantaten in der Arbeitsumgebung des Konstrukteurs (z.B. Modelliersystem – CAD) am Beispiel der konturlinienbasierten Modellrekonstruktion erörtert. Die gesamtheitliche Basis bildet eine durchgängig digitale Prozesskette zur Datenaufbereitung, Konstruktion und Fertigung. Die Anwendbarkeit der Methoden und zweier umgesetzter Demonstratoren wurde innerhalb eines interdisziplinär angelegten Projektes am realen Patientenfall bestätigt