William C. Scarfe

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.

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.

Position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria for the use of radiology in dental implantology with emphasis on cone beam computed tomography

A Position Paper Subcommittee of the American Academy of Oral and Maxillofacial Radiology (AAOMR) reviewed the literature since the original position statement on selection criteria for radiology in dental implantology, published in 2000. All current planar modalities, including intraoral, panoramic, and cephalometric, as well as cone beam computed tomography (CBCT) are discussed, along with radiation dosimetry and anatomy considerations. We provide research-based, consensus-derived clinical guidance for practitioners on the appropriate use of specific imaging modalities in dental implant treatment planning. Specifically, the AAOMR recommends that cross-sectional imaging be used for the assessment of all dental implant sites and that CBCT is the imaging method of choice for gaining this information. This document will be periodically revised to reflect new evidence.

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.

Cone Beam Computed Tomography in Implant Dentistry: A Systematic Review Focusing on Guidelines, Indications, and Radiation Dose Risks

PURPOSE The aim of the paper is to identify, review, analyze, and summarize available evidence in three areas on the use of cross-sectional imaging, specifically maxillofacial cone beam computed tomography (CBCT) in pre- and postoperative dental implant therapy: (1) Available clinical use guidelines, (2) indications and contraindications for use, and (3) assessment of associated radiation dose risk. MATERIALS AND METHODS Three focused questions were developed to address the aims. A systematic literature review was performed using a PICO-based search strategy based on MeSH key words specific to each focused question of English-language publications indexed in the MEDLINE database retrospectively from October 31, 2012. These results were supplemented by a hand search and gray literature search. RESULTS Twelve publications were identified providing guidelines for the use of cross-sectional radiography, particularly CBCT imaging, for the pre- and/or postoperative assessment of potential dental implant sites. The publications discovered by the PICO strategy (43 articles), hand (12), and gray literature searches (1) for the second focus question regarding indications and contraindications for CBCT use in implant dentistry were either cohort or case-controlled studies. For the third question on the assessment of associated radiation dose risk, a total of 22 articles were included. Publication characteristics and themes were summarized in tabular format. CONCLUSIONS The reported indications for CBCT use in implant dentistry vary from preoperative analysis regarding specific anatomic considerations, site development using grafts, and computer-assisted treatment planning to postoperative evaluation focusing on complications due to damage of neurovascular structures. Effective doses for different CBCT devices exhibit a wide range with the lowest dose being almost 100 times less than the highest dose. Significant dose reduction can be achieved by adjusting operating parameters, including exposure factors and reducing the field of view (FOV) to the actual region of interest.

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.

Upper airway segmentation and dimensions estimation from cone-beam CT image datasets

AbstractObjective To segment and measure the upper airway using cone-beam computed tomography (CBCT). This information may be useful as an imaging biomarker in the diagnostic assessment of patients with obstructive sleep apnea and in the planning of any necessary therapy. Methods With Institutional Review Board Approval, anonymous CBCT datasets from subjects who had been imaged for a variety of conditions unrelated to the airway were evaluated. DICOM images were available. A segmentation algorithm was developed to separate the bounded upper airway and measurements were performed manually to determine the smallest cross-sectional area and the anteriorposterior distance of the retropalatal space (RP-SCA and RP-AP, respectively) and retroglossal space (RG-SCA and RG-AP, respectively). A segmentation algorithm was developed to separate the bounded upper airway and it was applied to determine RP-AP, RG-AP, the smallest transaxial-sectional area (TSCA) and largest sagittal view airway area (LCSA). A second algorithm was created to evaluate the airway volume within this bounded upper airway. Results Measurements of the airway segmented automatically by the developed algorithm agreed with those obtained using manual segmentation. The corresponding volumes showed only very small differences considered clinically insignificant. Conclusion Automatic segmentation of the airway imaged using CBCT is feasible and this method can be used to evaluate airway cross-section and volume comparable to measurements extracted using manual segmentation.

A Comparison of Maxillofacial CBCT and Medical CT

In 1972, the independent findings of Hounsfield and Cormack revolutionized diagnostic imaging with the invention of the computed tomography (CT) scanner [1,2]. For the first time, practitioners had access to x-ray devices that could generate narrow cross-sectional images, usually perpendicular to the long axis of the human body, hence, the term computed axial tomography or CAT scan. This technology, fan-beam CT, was the first practical electronic application of the tomographic principal in diagnostic imaging [3] and provided images that eliminated the superimposition of adjacent anatomic structures inherent in conventional plain projection radiography and the blur of analog tomography. The availability of CT images facilitated new perspectives in imaging diagnosis by reducing much of the guesswork that was often interlaced with projection imaging. CT is now an essential imaging modality of the diagnostic algorithm for an increasing variety of clinical applications [4]. CT acquisition has subsequently been refined to incorporate a helical or spiral synchronous motion, fan-shaped beam, and multiple detector acquisition (MDCT), which enables fast scan times that provide highquality images that can be integrated to produce a volumetric dataset. Although CT has been available for more than 4 decades, its clinical applications in dentistry have been limited because of the high equipment cost, limited access because of the certificate-of-need requirements in some jurisdictions, and radiation dose considerations (Fig. 1A). Cone-beam computed tomography (CBCT) presents as a separate evolutionary arm to CT imaging. An early volumetric CT predecessor of CBCT, the Dynamic Spatial Reconstructor, was developed in the late 1970s by the Biodynamics Research Unit at the Mayo Clinic [5]. Subsequently applied for vascular imaging [6], CBCT prototypes based on C-arms were demonstrated as early as 1983. CBCT provided an alternate method of cross-section image production to fan-beam CT using a comparatively less-expensive radiation detector than conventional CT. The technology transfer of CBCT to dentistry first occurred in 1995. Italian co-inventors, Attilio Tacconi and Piero Mozzo, developed a CBCT system for the maxillofacial region that was designed and produced by QR, Inc of Verona, Italy. This unit, the NewTom DVT 9000 became the first commercial CBCT unit marketed specifically to the dental market, initially introduced in Europe in 1999. Although with little more than a decade of application in dentistry, CBCT has revolutionized oral and maxillofacial imaging. Similarities exist between technologies; however, differences in the image acquisition beam shape, as well as the x-ray generator and detecting system used, make CBCT stand independently as a simple and inexpensive approach to the concept of electronic sectional imaging focusing mostly on the maxillofacial region. This development has resulted in the clinical availability of a cross-sectional technology capable, for the most part, of providing members of the dental profession with a comparatively inexpensive 3-dimensional (3D) imaging modality, both in terms of cost and radiation burden. Although the first CBCT generation was similar to fan-beam CT in that image