Ralf Schulze

Artefacts in CBCT: a review

Artefacts are common in todays 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 todays CBCT scanners, as all artefacts are more or less directly related to it.

Correlation of cone beam computed tomography (CBCT) findings in the maxillary sinus with dental diagnoses: a retrospective cross-sectional study

This study was conducted to assess the coincidence of mucosal hyperplasia in the maxillary sinus and related clinical diagnoses of posterior maxillary teeth found in cone beam computed tomography (CBCT) scans. A total of 204 patients who underwent CBCT examinations between 2006 and 2008 were evaluated retrospectively. Clinical and CBCT findings were correlated using patient records. Absolute frequencies, odds ratios (OR), and 95% confidence intervals (95% CI) were calculated for statistical evaluations. There was a pronounced association between periodontitis and radiological signs of sinusitis. Basal mucosal wall thickening was more likely in patients with decayed and non-vital teeth compared to patients with sound teeth (OR = 5.2; 95% CI = 1.2–23.1). Basal mucosal wall thickening was also more likely than total mucosal thickening (OR = 10.4; 95% CI = 2.6–42.2). Patients with decayed and endodontically treated teeth were more likely to exhibit involvement of the basal wall (OR = 9.2; 95% CI = 3.3–25.2) than were patients with healthy teeth. CBCT examinations revealed a correlation between basal mucosal thickening in the maxillary sinus and decayed posterior maxillary teeth or periodontitis. Chronic symptoms involving the sinuses are one of the most common reasons for patients to consult physicians. One reason for chronic orofacial pain is the prevalence of undiagnosed sinus conditions.

Necessity of 3D visualization for the removal of lower wisdom teeth: required sample size to prove non-inferiority of panoramic radiography compared to CBCT

The availability of cone beam computed tomography (CBCT) and the numbers of CBCT scans rise constantly, increasing the radiation burden to the patient. A growing discussion is noticeable if a CBCT scan prior to the surgical removal of wisdom teeth may be indicated. We aimed to confirm non-inferiority with respect to damage of the inferior alveolar nerve in patients diagnosed by panoramic radiography compared to CBCT in a prospective randomized controlled multicentre trial. Sample size (number of required third molar removals) was calculated for the study and control groups as 183,474 comparing temporary and 649,036 comparing permanent neurosensory disturbances of the inferior alveolar nerve. Modifying parameter values resulted in sample sizes ranging from 39,584 to 245,724 respectively 140,024 to 869,250. To conduct a clinical study to prove a potential benefit from CBCT scans prior to surgical removal of lower wisdom teeth with respect to the most important parameter, i.e., nerval damage, is almost impossible due to the very large sample sizes required. This fact vice versa indicates that CBCT scans should only be performed in high risk wisdom tooth removals.

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, performed with four different sphere diameters and a commercial dental ccd-receptor system (pixel length: 0.0195 mm). The mouse-cursor based image evaluation revealed an average underestimation of the critical depth- (x-) coordinate decreasing with increasing radius (-30.3% for r=0.5 mm to 2.8% for r=2.5 mm). Intraobserver reliability (the standard deviation between three single cursor-based assessments) ranged between 0% and 8% of the actual true depth. The main source of the input error is associated with the assessment of the amount of elliptical distortion, where subpixel accuracy is demanded. Consequently, software-based automated image evaluation is required using available methods for pattern recognition and point-spread correction. Provided sufficient accuracy, the method provides an important tool for foreshortening correction, depth assessment, motion analysis, and 3-D reconstruction from two or more 2-D views.

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 methods 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 evaluated with the software. RESULTS 10 out of 79 (13%) were allocated to a patient movement. A threshold of 0.4 pixel/frame transition was empirically determined as indicating motion by visual assessment of the image sequence. Relative to this standard of reference, the software reached 80% sensitivity versus 67% specificity. CONCLUSIONS Optical flow seems to be an efficient concept for automated detection of patient motion on the projection images acquired during a CBCT scan.

GPU-Based Volume Reconstruction from Very Few Arbitrarily Aligned X-Ray Images

This paper presents a three-dimensional GPU-accelerated algebraic reconstruction method in a few-projection cone-beam setting with arbitrary acquisition geometry. To achieve artifact-reduced reconstructions in the challenging case of unconstrained geometry and extremely limited input data, we use linear methods and an artifact-avoiding projection algorithm to provide high reconstruction quality. We apply the conjugate gradient method in the linear case of Tikhonov regularization and the two-point-step-size gradient method in the nonlinear case of total variation regularization to solve the system of equations. By taking advantage of modern graphics hardware we achieve acceleration of up to two orders of magnitude over classical CPU implementations.

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

OBJECTIVES 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. STUDY DESIGN 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 therapy decision was examined as well. RESULTS On the basis of the information from intraoral photographs only, seven of the eight surgeons indicated that an additional radiographic examination was necessary for further therapy planning. For evaluation of the five radiographic BRONJ signs, CBCT provided significantly better values compared with OPTG (all P < .05). A before-and-after comparison showed that four of the eight surgeons changed their therapy concept after having three-dimensional CBCT information. The majority (6 of 8) of the surgeons considered that an additional CBCT was required for therapy planning, even after having studied the clinical photographs and OPTG images. CONCLUSION These data demonstrate a significant advantage of CBCT over OPTG for surgeons with regard to therapeutic planning for BRONJ.

Cone beam CT incidental findings: intracranial carotid artery calcification—a cause for concern

You may wonder why, as an exception, this editorial is co-authored by Arthur Friedlander from UCLA Dental School, LA. Well, he is currently actively involved in a discussion of obvious importance to the DMFR community. A recently published article noted that intracranial carotid artery calcifications (ICACs) were identified in 4 (2.4%) individuals (statistics recalculated by this correspondent) who were likely nested in the oldest cohort (n=169; age range, 50–85 years) of dental school clinic attendees having cone beam CT scans, in the main for implant placement.1 Using the best available evidence at the time, the authors concluded that no referral or intervention was warranted for these individuals because a study involving 406 (mainly Caucasian) patients (males, 60%; mean age, 62 ± 14 years) with ischaemic cerebrovascular symptoms (amaurosis fugax, transient ischaemic attack, stroke) could not associate the presence or volume of ICAC (as determined by multidetector CT angiography) with the patients’ symptomatic side.2 A review of more recent research, however, demonstrates the need to refer such patients to a physician because the data demonstrate that ICAC is a risk indicator of atherosclerotic disease burden across ethnic lines in both the cerebrovascular and cardiovascular distribution of healthy and symptomatic individuals. Specifically, the results of a recent study completed in Rotterdam, Netherlands, demonstrated that ICAC evidenced on non-contrast enhanced CT was prominently associated with the concomitant presence of MRI markers of vascular brain disease in healthy individuals.3 This investigation, conducted amongst 885 community-dwelling adults (males, 49.2%; mean age, 66.7 ± 5.5 years), demonstrated that higher calcification load and volume in the ICAC were prominently associated with MRI-determined increasing volume of white matter lesions known to be associated over time with development of cognitive impairment. These findings are substantiated by a study conducted in the USA which evaluated 108 consecutive multiethnic (African-American, Hispanic, Caucasian) patients (males 46%; mean age, 57.3 ± 12 years) admitted to the stroke service at Parkland Hospital in Dallas, TX.4 The researchers noted that extensive calcification of the ICAC on head CT was associated with high-grade stenosis (greater than or equal to 50%) on follow-up catheter-based cerebral angiographic study. These findings are supported by two other studies conducted in the Republic of Korea among groups of Asian patients admitted to major medical centers with symptomatic (acute ischaemic stroke/transient ischaemic attack) cerebrovascular disease. In the first project conducted amongst 159 consecutively treated patients (males, 61%; mean age, 66 ± 12 years), the extent of ICAC calcifications (as determined by unenhanced CT) was significantly associated with MRI-demonstrated periventricular and deep white matter hyperintensities and lacunar lesions.5 In the second Korean study evaluated, 314 patients (males, 65%; mean age, 66.3 ± 12.6 years), the severity of ICAC calcification on brain CT was significantly correlated with coronary artery calcium scores as determined by CT coronary angiography among patients previously believed free of atherosclerotic heart disease.6 Atherosclerosis is a generalized process affecting multiple vascular beds with arterial calcifications associated with more advanced states of disease. Cerebral calcification is a validated risk indicator of a diffuse atherosclerotic process in cerebral circulation and coronary artery atherosclerosis. The intention of this editorial is to make oral and maxillofacial radiologists aware that ICAC is a severe incidental finding that should definitely result in referral of these patients to physicians for further evaluation.

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-rater reproducibility (mean Cohens Kappa monitor: 0.49; printers: 0.44), but high diagnostic accuracy was found for all printers (areas [Az] underneath the ROC curves: 0.725 to 0.884). The overlap between the 95% Az confidence intervals of the mean indicate no significant differences. CONCLUSION Our preliminary findings indicate that dental radiographs may be evaluated on glossy paper prints of calibrated customary printers.

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.