Journal of Indian Academy of Oral Medicine and Radiology

REVIEW ARTICLE
Year
: 2017  |  Volume : 29  |  Issue : 1  |  Page : 30--34

Cone beam computed tomography: A boon for maxillofacial imaging


Sreenivas Rao Ghali1, Girish Katti1, Syed Shahbaz1, Chandrika Katti2,  
1 Department of Oral Medicine and Radiology, Al-Badar Rural Dental College and Hospital, Gulbarga, Karnataka, India
2 Department of Orthodontics, Al-Badar Rural Dental College and Hospital, Gulbarga, Karnataka, India

Correspondence Address:
Sreenivas Rao Ghali
Department of Oral Medicine and Radiology, Al-Badar Rural Dental College and Hospital, Gulbarga - 585 102, Karnataka
India

Abstract

In day to day practice, the radiographic techniques used individually or in combination suffer from some inherent limits of all planar two-dimensional (2D) projections such as magnification, distortion, superimposition, and misrepresentation of anatomic structures. The introduction of cone-beam computed tomography (CBCT), specifically dedicated to imaging the maxillofacial region, heralds a major shift from 2D to three-dimensional (3D) approach. It provides a complete 3D view of the maxilla, mandible, teeth, and supporting structures with relatively high resolution allowing a more accurate diagnosis, treatment planning and monitoring, and analysis of outcomes than conventional 2D images, along with low radiation exposure to the patient. CBCT has opened up new vistas for the use of 3D imaging as a diagnostic and treatment planning tool in dentistry. This paper provides an overview of the imaging principles, underlying technology, dental applications, and in particular focuses on the emerging role of CBCT in dentistry.



How to cite this article:
Ghali SR, Katti G, Shahbaz S, Katti C. Cone beam computed tomography: A boon for maxillofacial imaging.J Indian Acad Oral Med Radiol 2017;29:30-34


How to cite this URL:
Ghali SR, Katti G, Shahbaz S, Katti C. Cone beam computed tomography: A boon for maxillofacial imaging. J Indian Acad Oral Med Radiol [serial online] 2017 [cited 2021 Oct 16 ];29:30-34
Available from: https://www.jiaomr.in/text.asp?2017/29/1/30/212096


Full Text

 Introduction



Imaging is a significant diagnostic addition to the clinical evaluation of dental patients. With the increasing array of imaging modalities, dental radiology plays an innovative role in forming the diagnosis, treatment plan, and has a prognostic value.[1] In day to day practice, the intraoral and extraoral procedures, used individually or in combination, have some form of intrinsic limits of all planar two-dimensional (2D) projections, such as magnification, distortion, superimposition, and misrepresentation of structures. Several efforts have been made toward three-dimensional (3D) radiographic imaging. Although computed tomography (CT) has been available, its uses in dentistry has been limited because of access, cost, and dose considerations.[2]

Introduction of cone-beam computed tomography (CBCT) to imaging of the maxillofacial region led to a true shift from 2D to 3D approach. Literature provides an overview of the principles underlying this technology, as well as applications of CBCT in dentistry.[3] CT can be simply defined as the use of X-ray-based imaging method to produce 3D images usually displayed in the form of image slices. The CBCT machine uses cone-beam imaging technology rather than a fan-shaped X-ray beam as that used in conventional CT machines. This new generation scanner provides a complete 3D view of the maxilla, mandible, teeth, and supporting structures with relatively higher spatial resolution and lower radiation dose to the patient.[4]

Several terminologies are used for CBCT such as dental volumetric tomography, cone-beam volumetric tomography, cone-beam imaging, and dental computed tomography. The most frequently applied and preferred term is CBCT because it is a digital analog of film tomography in a more precise manner than that in CT, the X-ray is either cone-shaped or pyramidal, and the technology is not restricted to dentistry. The main feature of CBCT is that multiple planar projections are acquired by a single rotational scan to construct a volumetric dataset, from which inter-relational images can be generated.[2],[3],[4]

The image can be utilized for soft tissue enhancement, and can be shown in eye-popping color images and videos. Unlike conventional CT, which takes multiple passes and requires up to 45 min to get the images, CBCT unit rotates at 360° and its scans are of a single, large area in which the X-ray source and a reciprocating area detector move in tandem around the patient’s head, taking only few seconds to minutes to create an image. The X-ray beam exiting the patient is captured on a 2D detector, usually an amorphous silicon flat panel, or sometimes an image intensifier or charged couple device detector is utilized. The X-ray beam diameter ranges from 4–30 cm, the X-ray source and sensor goes around the patient’s head, and the sensor captures 160–599 images. These images are used to compute a spherical or cylindrical volume including all or a portion of the face.[5],[6],[7]

Application of CBCT in all fields of dentistry is brilliant because it has led to a revolution in maxillofacial radiology, facilitating the transition of dental diagnosis from 2D to 3D images and increasing the role of imaging from diagnosis to image management of operative procedures by using digital imaging and communications in medicine (DICOM). The most common indication for cone-beam imaging in dentistry are evaluation of the jaws for placement of dental implants, examination of teeth and facial structures for orthodontic treatment planning, assessment of temporomandibular joints (TMJs) for osseous degenerative changes, estimation of the proximity of the lower wisdom teeth to the mandibular nerve before surgical procedure, evaluation of teeth for root fracture or periapical disease, and assessment of bone for signs of infections, cysts, or tumors.[4],[6],[7]

Cone-beam imaging is quickly replacing conventional tomography because of its applications and benefits from viewing thin sections through the field of view without superimposition of complex anatomy onto the image. The CBCT ranks exceptionally well when considering the balance between high diagnostic yields, low risk, and low cost.[3]

 History



Since the time Sir Godfrey N. Hounsfield developed the first CT scanner in 1967, the field of CT technology has changed abundantly.[3],[5] In 1982, the first CBCT scanner was built for angiography at Mayo. After 1990, an initial period of rapid development, CT technology was rapidly established. In 1997, the department of radiology of the Nihon University School of Dentistry developed a dental radiology unit using a new technology known as limited cone-beam computed tomography. In 2000, the first CBCT to be approved by the FDA for dental use in the US was Newtom from Verona (Italy).[6],[7],[8]

 Principle of Cone-Beam Computed Tomography



The CBCT imaging employs the principle of tomosynthesis. In a single scan, the X-ray source and a reciprocating X-ray sensor rotate around the patient’s head and acquires multiple scans of the region of the interest. The acquired scans subsequently undergo a primary reconstruction mathematically, which replicate the patient’s anatomy into a single, 3D volume that comprises volume elements (VOXELS). The Voxel is as small as 0.1–0.4 mm for each of the cube face, and therefore, the image has moderately high resolution.[9]

Cone-beam scanners use a 2D digital array providing an area detector rather than a linear detector as in CT. This is joined with a 3D X-ray beam with circular collimation so that the resultant beam is in the shape of a cone, hence the name “cone-beam.” The scans include the region of interest (ROI). Only one rotational scan of the gantry is necessary to acquire enough data for image acquisition and reconstruction.

CBCT scans produce entire volumetric dataset from which the voxels are extracted. Voxel dimensions are dependent on the pixel size on the area detector. As a result CBCT units in general provide voxel resolutions that are isotropically equal in all three dimensions.[7] The field of view can be adjusted to include a portion of the entire maxillofacial region. The software allows the reformatting and viewing of the image data from any point of view in straight or curved planes. Using this software, the anatomy can be peeled away layer by layer to locate the desired anatomy in all three dimensions.[10]

During the rotation, 150–600 sequential planar projection scans of the field of view (FOV) are acquired in a complete arc. This procedure varies from a traditional medical CT, in which a fan-shaped X-ray beam in a helical progression is used to acquire individual image slices of the field of view and then stacks the slices to obtain a 3D representation, with each slice requiring a separate scan and 2D reconstruction. In comparison to CT, the CBCT incorporates the entire field of view in only one rotational sequence of the gantry to acquire enough data for image reconstruction.[11]

There are four components of CBCT image production [Figure 1]:{Figure 1}

Acquisition configurationImage detectionImage reconstructionImage display.

Acquisition configuration

The geometric pattern and acquisition mechanics for the CBCT technique are theoretically simple. A single partial or full rotational scan from an X-ray source takes place whereas a reciprocating detector moves synchronously with the scan around a fixed fulcrum.[1]

X-ray generation

During the scan, each projection image is made by sequential, single-image capture of the attenuated X-ray beams by the detector. Technically, the easiest method of exposing the patient is to use a constant beam of radiation during the rotation and allow the X-ray detector to sample the attenuated beam in its path. Alternately, the X-ray beam will be pulsed to coincide with the detector sampling, which implies that the actual exposure time is markedly less than the scanning time.[12]

Field of view

The size of the field of view or scan volume depends primarily on the detector size and shape, beam projection geometry, and the ability to collimate the beam. The shape of the scan volume can be either cylindrical or spherical. Collimation of the primary X-ray beam limits X-ray radiation exposure to the region of interest. Field size limitation ensures that an optimal field of view can be selected for each patient based on disease presentation and the region selected to be imaged.

CBCT systems can be categorized according to the available field of view or selected scan volume height as follows [Figure 2]:{Figure 2}

Localized region: Approximately 5 cm or less (e.g., dentoalveolar, temporomandibular joint)

Single arch: 5 cm to 7 cm (e.g., maxilla or mandible)

Inter arch: 7 cm to 10 cm (e.g., mandible and superiorly to include the inferior concha)

Maxillofacial: 10 cm to 15 cm (e.g., mandible and extending to nasion)

Craniofacial: Greater than 15 cm (e.g., from the lower border of the mandible to the vertex of the head).[12]

Image reconstruction

The speculation of reconstruction of 2D sections from their projections is distinguished. Several solutions to the reconstruction problem, such as transform-based, algebraic, and statistics have been proposed and used in practice. The most commonly used algorithm for tomographic reconstruction is filtered backprojection (FBP). As the name suggests, it consists of two steps – filtration of projection of the data and backprojection (BP).[12]

 Applications



The CBCT has revolutionized maxillofacial imaging extensively and has a wide range of applications in all the fields of dentistry ranging from diagnosis to treatment planning. CBCT has been frequently considered as the “gold standard” imaging of the oral and maxillofacial area. The CBCT should not be considered as a substitute for panoramic or conventional projection radiography but should be considered as a complimentary modality for specific applications.[13]

Cone-beam computed tomography in implantology

CBCT images helps to locate and determine the distance to vital anatomic structuresIt measures alveolar bone width and visualize bone contoursAids in Selection of the most suitable implant size and typeOptimize the implant location and angulations [Figure 3]Reduces surgery timeHelps to build patient confidence.[14]{Figure 3}

Cone-beam computed tomography in craniofacial fractures and impactions

Imaging of high-contrast bony structural pathology, such as craniofacial fractures, is a logical application for CBCT. In patients with facial trauma, it is used to characterize a mandibular head fracture, dental root fractures, and the displacement of anterior maxillary teeth. CBCT aids in visualizing an impacted tooth’s position in relation to the surrounding vital structures[1],[15] [Figure 4].{Figure 4}

cone-beam computed tomography in orthodontics

Allows 3D views of vital structuresAids in 3D evaluation of impacted tooth position and anatomyTMJ assessments of condylar anatomy in three dimensionsAirway assessment is outstandingOrthognathic growth assessments and treatment planning is in true 1:1 imagingAssessment of skeletal symmetryPlanning for placement of dental implants for tooth restoration or orthodontic anchorage and for placement of temporary anchorage devices.[16]

Temporomandibular joint

Morphologic changes of the TMJ depicted with CBCT imaging are useful in diagnosing pathologic processes such as degenerative changes and ankylosis, joint remodelling after diskectomy, malocclusion, and congenital and developmental malformations.[17]

Oral and maxillofacial pathology

It provides more accurate information related to size, extent, location, and the relation to effect on nearby anatomical structures.Helps to monitor the progression of the pathology as well as the success of treatment.[18]

Sinus and airway studies

CBCT scan can be used to visualize the sinuses and the entire airway path from the nasal and oral entrances to the laryngeal spaces:

To identify anatomical bordersTo determine the degree of infection and presence of polypsAiding in airway studies for diagnosis and treatment of obstructive sleep apnea.[19]

 Advantages and Disadvantages



Advantages of cone-beam computed tomography

Rapid scan timeImage accuracyHigh image resolutionBeam limitationReduced patient radiation dosePatient’s compliance.[1],[2]

Disadvantages of cone-beam computed tomography

Image noisePoor soft tissue contrastArtifacts.[1],[2]

 Future Directions



Virtual imaging, combined three-dimensional photography

The next generation of CT imaging in dentistry is imminent. The 3D imaging that CBCT generates allows for far more accurate diagnosis, treatment planning and monitoring, and analysis of outcomes, which were difficult with conventional 2D images. Recognition of this innovative imaging technology, coupled with rapid increase in understanding the biological processes of maxillofacial growth and development, which will help in creating and interacting with virtual models of patients’ tooth and jaw structures that enable to provide a much higher level of treatment.[20]

CT scanners have evolved into a new dimension; “ultra cone-beam CT scanners.” Ultra CBCT imaging provides important information about the 3D structure of blood vessels, nerves, soft tissue, and bone. The contrast-enhanced territories highlighted by CBCT with selective intra-arterial contrast media administration were used to predict the distribution of microspheres. This CBCT imaging modality will occupy a place in routine practice with newer advancement. It will further improve the diagnostic abilities and hence enhance the treatment planning in this fast changing arena of dental sciences.[21]

 Conclusion



The CBCT ranks extremely high when considering the balance between high diagnostic yield, low cost, and low risk to the patient. CBCT allows “real time” creation of images not only in the axial plane but also 2D images in the coronal, sagittal, and even oblique or curved image planes. In addition, CBCT data are acquiescent to reformation in a volume, rather than a slice, providing 3D information with minimal distortion.[2]

CBCT is capable of imaging hard-tissue and most soft-tissue structures. However, this technology does not have the ability to precisely map muscles and their attachments. These structures would have to be imaged using conventional magnetic resonance imaging technology. Undoubtedly, future developments in CBCT technology will result in systems with even more favorable diagnostic yields. If a drop in prices occurs, CBCT imaging will become the primary form of dental imaging. At present, CBCT imaging is a highly useful, indispensable part of the dental imaging armamentarium.[2],[3],[4]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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