A method for automatic forensic facial reconstruction based on dense statistics of soft tissue thickness.

In this paper, we present a method for automated estimation of a human face given a skull remain. The proposed method is based on three statistical models. A volumetric (tetrahedral) skull model encoding the variations of different skulls, a surface head model encoding the head variations, and a dense statistic of facial soft tissue thickness (FSTT). All data are automatically derived from computed tomography (CT) head scans and optical face scans. In order to obtain a proper dense FSTT statistic, we register a skull model to each skull extracted from a CT scan and determine the FSTT value for each vertex of the skull model towards the associated extracted skin surface. The FSTT values at p…

Influence of Three-dimensional Imaging on Implant Treatment Planning: Implant Diameter and Length

Aim To investigate the influence of the radiographic modalities panoramic radiography (PR) and cone beam computed tomography (CBCT) on selection of implant length and diameter. Materials and methods Potential implant sites (59 sites, 40 patients) with available PRs and CBCTs were selected from the databases of two University dental schools. Six experienced clinicians were asked to select the appropriate implant length and diameter based on PR and CBCT. Results were compared with the actual surgical procedure and intra- /interrater agreement was calculated using Cohen's kappa. Results On average, greater implant length was more often planned based on PR (24.2 vs 8.8% with CBCT), while wider …

Surgical evaluation of panoramic radiography and cone beam computed tomography for therapy planning of bisphosphonate-related osteonecrosis of the jaws

The purpose of this retrospective study was to compare the clinical significance of panoramic radiography (orthopantomography [OPTG]) and cone beam computed tomography (CBCT) for therapy planning of bisphosphonate-related osteonecrosis of the jaw (BRONJ) by surgeons.Using standardized questionnaire, eight maxillofacial surgeons evaluated intraoral photographs of the clinical situation of 14 patients with BRONJ as well as the corresponding radiographic images (OPTG, CBCT). The presence of five typical BRONJ signs (bone-remodeling, periosteal reaction, osteosclerosis, sequestra, and continuity of cortical bone) was evaluated with OPTG and CBCT. The influence of radiologic information on thera…

Alignment of cone beam computed tomography data using intra-oral fiducial markers.

This article illustrates a new method to align and merge two partially overlapping volumes each of them generated by cone beam computed tomography (CBCT). The aggregate volume covers a larger area of investigation and is determined by localizing one fixed LEGO brick in both of the primal volumes. Based on the LEGO brick an approximate registration of the volumes is determined. Afterwards we improve the transformation by minimizing the difference in overlapping space. In this paper we present a method which automates these two steps and provides an aligned volume.

Artefacts in CBCT: a review

Artefacts are common in today's cone beam CT (CBCT). They are induced by discrepancies between the mathematical modelling and the actual physical imaging process. Since artefacts may interfere with the diagnostic process performed on CBCT data sets, every user should be aware of their presence. This article aims to discuss the most prominent artefacts identified in the scientific literature and review the existing knowledge on these artefacts. We also briefly review the basic three-dimensional (3D) reconstruction concept applied by today's CBCT scanners, as all artefacts are more or less directly related to it.

Presurgical evaluation of bony implant sites using panoramic radiography and cone beam computed tomography—influence of medical education

The aim of this study was to compare the subjective quality rating of panoramic radiography (PAN) and CBCT in the planning of dental implant procedures by clinicians with different educational backgrounds.Radiographic images (PAN and CBCT) of 42 patients were examined as follows: the maxillary (MX) anterior region of patients, the MX posterior region of 16 patients and the mandibular (MD) posterior region of 16 patients. These sites were used for planning of dental implant insertion. Data sets were analyzed by examiners with different training backgrounds: three general practitioners (GP), three oral surgeons (OS) and three maxillofacial surgeons (MS). A standardized questionnaire in a stan…

Epulis granulomatosa as an oral manifestation of Klippel-Trénaunay syndrome

The Klippel-Trenaunay syndrome (KTS) was first described by Klippel and Trenaunay in 1900. It is characterized by the triad of hemihypertrophy of soft and hard tissue, naevus flammeus and venous varicosity in the affected area. Though all oral tissues may be affected, only 5% of KTS show manifestations in the head and neck region. Only three cases are described with an oral manifestation, showing gingival overgrowth clinically and histologically corresponding to a pyogenic granuloma. It is still uncertain whether the combination of gingival fibromatosis and KTS is significant or coincidental. We report about a 25-year-old patient with KTS and recidivous gingival fibromatosis, clinically and…

Auto calibration of a cone-beam-CT

Purpose: This paper introduces a novel autocalibration method for cone-beam-CTs (CBCT) or flat-panel CTs, assuming a perfect rotation. The method is based on ellipse-fitting. Autocalibration refers to accurate recovery of the geometric alignment of a CBCT device from projection images alone, without any manual measurements. Methods: The authors use test objects containing small arbitrarily positioned radio-opaque markers. No information regarding the relative positions of the markers is used. In practice, the authors use three to eight metal ball bearings (diameter of 1 mm), e.g., positioned roughly in a vertical line such that their projection image curves on the detector preferably form l…

Role of ambient light in the detection of contrast elements in digital dental radiography.

Objective This study aimed to evaluate the effect of different ambient light levels on observer detection of small contrast differences in a contrast phantom by using a high-end liquid crystal display (LCD) monitor. Study Design An aluminum step wedge was converted into a contrast phantom by the addition of bore holes. Radiographic images of the contrast elements were presented to 20 observers. Images were displayed in random order under different ambient light levels (0, 50, 200, and 500 lux) twice, and the observers had to determine if contrast elements were visible. Sensitivity and specificity were determined to calculate areas under receiver operating characteristic curves and Friedmann…

Simple computation of the approximated modulation transfer function (MTF) using spreadsheet-software: method and evaluation in five maxillofacial CBCT-devices

OBJECTIVES: To develop a simple way to compute the approximated modulation transfer function (MTF) manually using conventional spreadsheet software. METHODS: Basing on an edge-image a method was developed, facilitating computation of the edge spread and line spread function in open-source spreadsheet software (Gnumeric; http://projects.gnome.org/gnumeric/downloads.shtml). By means of the integrated fast Fourier transformation Fourier coefficients are obtained from the line spread function which can then be plotted vs spatial frequency to obtain MTF-plots. For the experimental evaluation an edge test object was exposed in five commercial CBCT devices for maxillofacial applications. RESULTS: …

Accuracy in Detecting Artificial Root Resorption in Panoramic Radiography versus Tomosynthetic Panoramic Radiographs.

The aim of this study was to compare the detection accuracy of panoramic radiography (PAN) and tomosynthetically reconstructed panoramic radiography (TPAN) for the detection of artificial external root resorption in a multiobserver approach.Thirty-six teeth in 5 dry human mandibles were prepared with artificial root resorption by means of diamond bur defects (0.8, 1.0, and 1.2 mm). The samples were exposed in a digital panoramic radiographic unit in a predetermined appropriate position using a wax layer (6.25 mm thickness) as soft tissue scatter equivalent and a water-filled plastic bottle to mimic the absorption of the cervical spine. This resulted in 5 panoramic radiographs and 5 tomosynt…

Software for automated application of a reference-based method fora posterioridetermination of the effective radiographic imaging geometry

Objectives: Presentation and validation of software developed for automated and accurate application of a reference-based algorithm (reference sphere method: RSM) inferring the effective imaging geometry from quantitative radiographic image analysis. Methods: The software uses modern pattern recognition and computer vision algorithms adapted for the particular application of automated detection of the reference sphere shadows (ellipses) with subpixel accuracy. It applies the RSM algorithm to the shadows detected, thereby providing threedimensional Cartesian coordinates of the spheres. If the three sphere centres do not lie on one line, they uniquely determine the imaging geometry. Accuracy …

Quality of individually calibrated customary printers for assessment of typical dental diagnoses on glossy paper prints: a multicenter pilot study.

Objective The objective of this study was to compare dental radiographs printed on glossy paper from calibrated low-cost printers with monitor display. Study design Three typical intraoral radiographs were selected and a questionnaire was developed with questions assessing accuracy and subjective quality. A test pattern was designed for printer calibration. After calibration, radiographs were printed on glossy paper with 3 ink-jet and 2 thermo-sublimation printers. Sixteen raters evaluated the printed radiographs, 9 of them also on standardized viewing monitors. Subjective ratings were compared, and an ROC-analysis based on expert-consensus monitor readings was performed. Results Low inter-…

Editorial: guidelines for oral and maxillofacial radiology

In vitro perception of low-contrast features in digital, film, and digitized dental radiographs: A receiver operating characteristic analysis

Objective To compare experimentally the image quality of charged-coupled device (CCD)-based digital, flatbed scanner digitized, and dental film radiographs. Study design High-contrast standardized radiographs of an aluminum step wedge containing boreholes were obtained on dental radiographic film (F) and a CCD receptor (D). Digitization (S) was done with a flatbed scanner. Each radiograph was separated into 23 single images, 18 of which showed a dark spot. Thirty observers indicated their confidence on the visibility of the spots for a receiver operating characteristic (ROC) analysis. Results Mean Az values (area beneath the ROC curves) differed significantly (P < .05), being highest for D …

Editorial 1/2018

Influence of a Commercial Lead Apron on Patient Skin Dose Delivered During Oral and Maxillofacial Examinations under Cone Beam Computed Tomography (CBCT)

The purpose of this paper is to investigate the impact of a commercial lead apron on patient skin dose delivered during maxillofacial CBCT in five critical regions by means of solid-state-dosimetry. Five anatomical regions (thyroid gland, left and right breast, gonads, back of the phantom torso) in an adult female anthropomorphic phantom were selected for dose measurement by means of the highly sensitive solid-state dosimeter QUART didoSVM. Ten repeated single exposures were assessed for each patient body region for a total of five commercial CBCT devices with and without a lead apron present. Shielded and non-shielded exposures were compared under the paired Wilcoxon test, with absolute an…

Viewing patterns regarding panoramic radiographs with different pathological lesions: an eye-tracking study.

Objective: The aim of this study was to examine how dental students vary their viewing patterns of panoramic radiographs during different levels of dental education. Methods: Two groups of students (total number = 48, n = 24) in different grades (second and fifth clinical semester) were compared. The second clinical semester participated twice, as during the second clinical semester a specific lecture on dental radiology and diagnosis is held. The first viewing took place at the beginning of the semester (2a), the second at the end of it (2e). The fifth semester (5e) represents students shortly before graduation. While viewing 20 panoramic radiographs showing specific pathologies, the eye m…

Automated detection of patient movement during a CBCT scan based on the projection data.

Objectives To develop an automated procedure to detect patient motion on the projection images acquired during a cone beam computed tomography (CBCT) scan and to evaluate the method's feasibility on small real-world CBCT images in relation to visual assessment. Methods Based on optical flow theory, software was developed using the sequence of the projection images of a CBCT machine for automated detection of patient motion. Averaged acceleration vectors were used as measurement data and compared with visual assessment of the projection images displayed as video. Seventy-nine CBCT data sets (small field-of-view: 40 mm) from our patient database were selected in a sequential fashion and evalu…

2020—a year of changes

Accurate registration of random radiographic projections based on three spherical references for the purpose of few-view 3D reconstruction

Precise registration of radiographic projection images acquired in almost arbitrary geometries for the purpose of three-dimensional (3D) reconstruction is beset with difficulties. We modify and enhance a registration method [R. Schulze, D. D. Bruellmann, F. Roeder, and B. d'Hoedt, Med. Phys. 31, 2849-2854 (2004)] based on coupling a minimum amount of three reference spheres in arbitrary positions to a rigid object under study for precise a posteriori pose estimation. Two consecutive optimization procedures (a, initial guess; b, iterative coordinate refinement) are applied to completely exploit the reference's shadow information for precise registration of the projections. The modification h…

Three-Dimensional Classification of Lower Third Molars and Their Relationship to the Mandibular Canal.

PURPOSE To develop a novel classification making full use of radiographic three-dimensional (3D) information to describe the position, geometric configuration of a mandibular third molar (M3M) and its spatial relation to neighboring structures such as the mandibular canal (MC). The classification presented in this study helps to establish a common language and serves as a framework for further studies, for example, on 3D parameters influencing prognosis of the M3M and level of difficulty associated with its removal. MATERIAL AND METHODS A total of 8 parameters were included in the classification including position, the cranio-caudal height, the number of roots of the M3M as well as its spat…

Projection-based improvement of 3D reconstructions from motion-impaired dental cone beam CT data.

Purpose Computed tomography (CT) and, in particular, cone beam CT (CBCT) have been increasingly used as a diagnostic tool in recent years. Patient motion during acquisition is common in CBCT due to long scan times. This results in degraded image quality and may potentially increase the number of retakes. Our aim was to develop a marker-free iterative motion correction algorithm that works on the projection images and is suitable for local tomography. Methods We present an iterative motion correction algorithm that allows the patient's motion to be detected and taken into account during reconstruction. The core of our method is a fast GPU-accelerated three-dimensional reconstruction algorith…

Editorial: CBCT special issue

In the dental community, it is a common belief that CBCT was invented for oral and maxillofacial imaging. Of course, we know that this is a myth since the technique of a volumetric CT is indeed much older and dates back to the late 1970s.1,2 Considering that CT was introduced in 1973, its volumetric counterpart was developed very soon thereafter driven by the need for high spatial and temporal resolution that a conventional CT at that time was not able to achieve. However, successful marketing of the technique indeed was much later, and certainly a consequence of the publication of “A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results” by Mozz…

Total Variation Regularization in Digital Breast Tomosynthesis

We developed an iterative algebraic algorithm for the reconstruction of 3D volumes from limited-angle breast projection images. Algebraic reconstruction is accelerated using the graphics processing unit. We varied a total variation (TV)-norm parameter in order to verify the influence of TV regularization on the representation of small structures in the reconstructions. The Barzilai-Borwein algorithm is used to solve the inverse reconstruction problem. The quality of our reconstructions was evaluated with the Quart Mam/Digi Phantom, which features so-called Landolt ring structures to verify perceptibility limits. The evaluation of the reconstructions was done with an automatic LR detection a…

Regelrechte Röntgenanatomie im Schnittbild der Digitalen Volumentomographie

Normale Anatomie, Normvariante oder Pathologie – diese Frage ist haufig einfach, aber gelegentlich auch nur sehr schwer zu beantworten. Ausgangspunkt bei der Beurteilung eines jeden Rontgenbildes ist das Wissen uber die gesunde, regular vorzufindende Anatomie. Dieses Kapitel widmet sich als vielleicht wichtigstes Grundlagenkapitel nicht nur der Anatomie von Ober- und Unterkiefer inklusive der Zahne, sondern auch der Kieferhohle und dem Kiefergelenk. Daruber hinaus wird die normale Anatomie aller Regionen aufgezeigt, die zumindest gelegentlich in DVT-Aufnahmen mit abgebildet werden und die im Sinne einer vollstandigen Befundung des Datensatzes mit beurteilt werden mussen. Konkret sind dies: …

Editorial 1/2016

It is with great pleasure to wish all our readers, authors and reviewers a happy and healthy new year 2016! Dentomaxillofacial Radiology is fortunate to look back on some rather successful years. Our speciality, that is, oral and maxillofacial (radiological) imaging gained increasing importance over the past decade, which is predominantly a result of the success of CBCT. Lately, we have seen an increasing number of articles (e.g. Petersen Johan Aps Gang Li

Determination of projection geometry from quantitative assessment of the distortion of spherical references in single-view projection radiography

A method is introduced, inferring the three-dimensional (3-D) location from the 2-D radiographic shadow of an opaque spherical reference body of known radius by considering its elliptical distortion, the 2-D shadow location and a known source-to-receptor distance. Three noncollinear spheres fixed to a rigid object constitute all possible degrees of freedom, i.e., the entire 3-D imaging geometry. The method may be used (a) to determine the 3-D imaging geometry from a single 2-D view and (b) to correct for foreshortening of object distances coplanar with the plane defined by the sphere triplet. Apart from the mathematical background the article describes a small feasibility experiment, perfor…

Implant treatment planning regarding augmentation procedures: panoramic radiographs vs. cone beam computed tomography images.

Objectives To evaluate the impact of cone beam computed tomography (CBCT) imaging on treatment planning regarding augmentation procedures for implant placement. Material and methods Panoramic radiographs and CBCT images of 40 patients requesting single-tooth implants in 59 sites were retrospectively analyzed by six specialists in implantology, and treatment planning was performed. Therapeutic recommendations were compared with the surgical protocol performed initially. Results Bone height estimation from panoramic radiographs yielded to higher measures and greater variability compared to CBCT. The suggested treatment plan for lateral and vertical augmentation procedures based on CBCT or pan…

Diagnostic yield of ink-jet prints from digital radiographs for the assessment of approximal carious lesions: ROC-analysis

Abstract Aims To investigate the diagnostic quality of different quality, individually calibrated ink-jet printers for the very challenging dental radiographic task of approximal carious lesion detection. Materials and methods A test-pattern evaluating resolution, contrast and homogeneity of the ink-jet prints was developed. 50 standardized dental radiographs each showing two neighbouring teeth in natural contact were printed on glossy paper with calibrated, randomly selected ink-jet printers (Canon S520 and iP4500, Epson Stylus Photo R2400). Printing size equalled the viewing size on a 17″ cathode-ray-tube monitor daily quality-tested according to German regulations. The true caries status…

3D Reconstructions from Few Projections in Oral Radiology

Established techniques for three-dimensional radiographic reconstruction such as computed tomography (CT) or, more recently cone beam computed tomography (CBCT) require an extensive set of measurements/ projections from all around an object under study. The x-ray dose for the patient is rather high. Cutting down the number of projections drastically yields a mathematically challenging reconstruction problem. Few-view 3D reconstruction techniques commonly known as “tomosynthetic reconstructions” have gained increasing interest with recent advances in detector and information technology.

Effects of minute misregistrations of prefabricated markers for image-guided dental implant surgery: an analytical evaluation

Objectives The goal of the present study was to develop a theoretical analysis of errors in implant position, which can occur owing to minute registration errors of a reference marker in a cone beam computed tomography volume when inserting an implant with a surgical stent. Material and methods A virtual dental-arch model was created using anatomic data derived from the literature. Basic trigonometry was used to compute effects of defined minute registration errors of only voxel size. The errors occurring at the implant's neck and apex both in horizontal as in vertical direction were computed for mean ±95%-confidence intervals of jaw width and length and typical implant lengths (8, 10 and 1…

Metal artifact reduction in x-ray computed tomography: Inpainting versus missing value

A comparison of algorithms for reduction of metal artifacts in x-ray cone beam computed tomography (CBCT) is presented. In the context of algebraic reconstruction techniques (ART) several inpainting algorithms in the image domain are evaluated against missing data strategies. A GPU-based iterative framework is employed for a meaningful comparison of both. Simulation results from an extended Shepp-Logan phantom and real world dental data are given.