Allan G. Farman

What is Cone-Beam CT and How Does it Work?

This article on x-ray cone-beam CT (CBCT) acquisition provides an overview of the fundamental principles of operation of this technology and the influence of geometric and software parameters on image quality and patient radiation dose. Advantages of the CBCT system and a summary of the uses and limitations of the images produced are discussed. All current generations of CBCT systems provide useful diagnostic images. Future enhancements most likely will be directed toward reducing scan time; providing multimodal imaging; improving image fidelity, including soft tissue contrast; and incorporating task-specific protocols to minimize patient dose.

Skeletal maturation evaluation using cervical vertebrae.

Lateral cephalometric and left hand-wrist radiographs from the Bolton-Brush Growth Center at Case Western Reserve University were reviewed a posteriori to develop a cervical vertebrae maturation index (CVMI). By using the lateral profiles of the second, third and fourth cervical vertebrae, it was possible to develop a reliable ranking of patients according to the potential for future adolescent growth potential.

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

OBJECTIVE To compare accuracy of linear measurements made on cone beam computed tomographic (CBCT) derived 3-dimensional (3D) surface rendered volumetric images to direct measurements made on human skulls. MATERIALS AND METHODS Twenty orthodontic linear measurements between anatomical landmarks on 23 human skulls were measured by observers using a digital caliper. The skulls were imaged with CBCT and Dolphin 3D (version 2.3) software used to generate 3D volumetric reconstructions (3DCBCT). The linear measurements between landmarks were computed by a single observer three times and compared to anatomic dimensions using Students t-test (P < or = .05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were calculated. RESULTS The ICC for 3DCBCT (0.975 +/- 0.016) was significantly less than for skull (0.996 +/- 0.007) measurements. Mean percentage measurement error for 3DCBCT (2.31% +/- 2.11%) was significantly higher than replicate skull measurements (0.63% +/- 0.51%). Statistical differences between 3DCBCT means and true dimensions were found for all of the midsagittal measurements except Na-A and six of the 12 bilateral measurements. The mean percentage difference between the mean skull and 3D-based linear measurements was -1.13% (SD +/- 1.47%). Ninety percent of mean differences were less than 2 mm, and 95% confidence intervals were all less than 2 mm except for Ba-ANS (3.32 mm) and Pog-Go(left) (2.42 mm). CONCLUSIONS While many linear measurements between cephalometric landmarks on 3D volumetric surface renderings obtained using Dolphin 3D software generated from CBCT datasets may be statistically significantly different from anatomic dimensions, most can be considered to be sufficiently clinically accurate for craniofacial analyses.

Use of Cone Beam Computed Tomography in Endodontics

Cone Beam Computed Tomography (CBCT) is a diagnostic imaging modality that provides high-quality, accurate three-dimensional (3D) representations of the osseous elements of the maxillofacial skeleton. CBCT systems are available that provide small field of view images at low dose with sufficient spatial resolution for applications in endodontic diagnosis, treatment guidance, and posttreatment evaluation. This article provides a literature review and pictorial demonstration of CBCT as an imaging adjunct for endodontics.

Linear accuracy of cone beam CT derived 3D images.

OBJECTIVE To compare the in vitro reliability and accuracy of linear measurements between cephalometric landmarks on cone beam computed tomography (CBCT) 3D volumetric images with varying basis projection images to direct measurements on human skulls. MATERIALS AND METHODS Sixteen linear dimensions between 24 anatomic sites marked on 19 human skulls were directly measured. The skulls were imaged with CBCT (i-CAT, Imaging Sciences International, Hatfield, Pa) at three settings: (a) 153 projections, (b) 306 projections, and (c) 612 projections. The mean absolute error and modality mean (+/- SD) of linear measurements between landmarks on volumetric renderings were compared to the anatomic truth using repeated measures general linear model (P < or = .05). RESULTS No difference in mean absolute error between the scan settings was found for almost all measurements. The average skull absolute error between marked reference points was less than the distances between unmarked reference sites. CBCT resulted in lower measurements for nine dimensions (mean difference range: 3.1 mm +/- 0.12 mm to 0.56 mm +/- 0.07 mm) and a greater measurement for one dimension (mean difference 3.3 mm +/- 0.12 mm). No differences were detected between CBCT scan sequences. CONCLUSIONS 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. Because the fiducial landmarks on the skulls were not radio-opaque, the inaccuracies found in measurement could be due to the methods applied rather than to innate inaccuracies in the CBCT scan reconstructions or 3D software employed.

American Academy of Oral and Maxillofacial Radiology executive opinion statement on performing and interpreting diagnostic cone beam computed tomography

The American Academy of Oral and Maxillofacial Radiology (AAOMR) is the professional organization representing oral and maxillofacial radiologists in the United States. The Academy is a nonprofit professional society the primary purposes of which are to advance the science of radiology, improve the quality and access of radiologic services to the patient, and encourage continuing education for oral and maxillofacial radiologists, dentists, and persons practicing oral and maxillofacial imaging in allied professional fields. The AAOMR embraces the introduction of cone beam computed tomography (CBCT) as a major advancement in the imaging armamentarium available to the dental profession. The AAOMR is currently in the process of developing a position paper on appropriate application of CBCT to provide evidence-based guidelines. In the interim, the Executive Committee (EC) of the AAOMR considers it necessary to provide an opinion document addressing the principles of application of CBCT as it relates to acquisition and interpretation of maxillofacial imaging in dental practice.

Future trends in dental radiology

Direct digital dental radiographic systems offer the potential to radically change the way dentists diagnose and treat dental pathoses. They offer instantaneous availability of radiographs, markedly lower patient radiation exposure, and the elimination of developing chemicals and developing equipment. The storage of dental radiographs as digital data permits their transmittal over phone lines facilitating phone consultations and may someday allow expedited authorization of treatment plans by dental insurance companies. With the use of digital subtraction radiology the dental practitioner will be able to diagnose periodontal disease progression and dental caries progression long before current techniques can detect a change. With tuned aperture computed tomography, the owner of a filmless digital system can make tomographic radiographs that allow the visualization of slices through areas of interest without having to buy additional hardware. Computer-aided diagnosis will facilitate the detection of proximal dental caries and osteoporosis, and may someday allow automated tracing of cephalometric radiographs.

A 3-D reconstruction system for the human jaw using a sequence of optical images

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patients dental occlusion using an intraoral video camera. A modified shape from shading (SFS) technique, using perspective projection and camera calibration, extracts the 3-D information from a sequence of two-dimensional (2-D) images of the jaw. Data fusion of range data and 3-D registration techniques develop the complete jaw model. Triangulation is then performed, and a solid 3-D model is reconstructed. The system performance is investigated using ground truth data, and the results show acceptable reconstruction accuracy.

Soft tissue profile: A survey of African-American preference

Soft tissue profile is a critical area of interest in the development of an orthodontic treatment plan. This study was designed to elicit the current soft tissue profile preference of African-American respondents. Results indicate that: (1) African-American male and female subjects prefer relatively flat profiles, with varied fullness of the lips. (2) African-American male and female subjects prefer the male subjects to have more protrusive profiles than the female subjects. (3) Respondents do not always correctly select their own profile type. (4) More than a third of the respondents desire a change in their own profile.

Radiographic detection of accessory/lateral canals: Use of RadioVisioGraphy and hypaque

The diagnostic accuracy of RadioVisioGraphy (RVG-S) and conventional film images with and without the use of a radiopaque contrast media were compared for the detection of accessory/lateral canals. Forty-nine root canals, 13 with verified lateral canals, were endodontically prepared and imaged using both conventional intraoral dental film (E-speed) and three modes of RVG-S digital radiography (normal, inverse, zoom) before and after introduction of Hypaque-M, 90%. Images were presented to seven viewers; however, three demonstrated only fair intrarater reliability and were excluded. Overall sensitivity was low. RVG images were slightly more sensitive than conventional film images. Specificities, positive predictive values, and negative predictive values were low and showed no differences between modalities. It was concluded that the diagnostic accuracy of both film and RVG-S digital radiographic images for the detection of accessory/lateral canals, either alone or in combination with radiopaque contrast material, is low.