How Image Reconstruction And Processing Takes Place in CBCT?
Cone beam imaging technology, most commonly called cone-beam computed tomography (CBCT), radiographically images the object in question in the axial, coronal, and sagittal planes.
In computed tomography, the structure of an object is always obtained by penetration of X-rays. The detector cells acquire X-ray measurements that measure the amount of radiation penetrating the source in different directions. This is referred to as image acquisition. After the completion of image reconstruction in different planes (mainly sagittal, coronal, and axial), the computer components will store and make the CT (computed tomography) image available for display in any form of imaging software.
Unlike CT scanning, CBCT uses collimators that block the X-ray emission into undesired areas other than the object to be exposed or imaged. Immediately after the step of image reconstruction, the image needs to be processed by choosing a field of view (FOV), a region in space where the image is obtained.
How Is the Image Attenuation and Accuracy With CBCT?
Attenuation in radiography is the process by which the number of particles through the radiating X-ray beam is absorbed and scattered so that the radiation exposure to the subject is reduced. Attenuation is measured in absolute events of inverse length (mm-1 or cm-1). In CT and CBCT, attenuation is measured in Hounsfield units (HU).
The importance of attenuation in CT and CBCT scanning is that the reconstructed image is converted to HU and then made available for display in the imaging software in the computer systems. However, as a result of CT attenuation, there are certain artifacts or radiographic changes like beam hardening. Beam hardening is mainly seen in two different manifestations of either streaking or cupping artifacts. In streaking, the image obtained appears to be distorted with multiple dark bands, while in cupping artifacts, the center of the image is affected and appears dense. If these artifacts are left without any rectification in the final image then the resultant image not only appears dense but also distorted which can be differentiable only to clinicians.
In CBCT, the image dimension is represented by voxels. The voxel elements are isotropic, meaning they represent the absorption of the X-rays uniformly in every direction (which is a great advantage because in all the three major orthogonal planes), the image acquired can be measured equally in terms of voxel elements. The voxel sizes used in CBCT also vary as they are available in different sizes as in 0.2 mm, 0.3 mm, and 0.4 mm. The voxel size depends on the size of the unit detector of CBCT. In advanced CBCT imaging, a lesser voxel size is used as the greater the voxel size, the lesser the resolution of the resultant radiographic image.
What Are the Components of CBCT?
Along with these design changes, better stabilization devices for the patient's head and chin rest have been modified over the years. Mechanical changes included the switch to smaller, flat-panel silicon detectors with better image quality compared with the bulkier, cumbersome, and more costly image-intensifier detectors. The main components of a CBCT system are:
A rotating gantry in which the patient stands or sits (that moves the X-ray to the object source and fires the beam to the detector cells).
The X-ray source.
Detector arrays with rejection grids (silicon detectors or amorphous silica detectors).
A computer that runs imaging software for image reconstruction and storage.
The stored image is then displayed.
What Are the Applications of CBCT?
Oral and maxillofacial radiology over the last few decades has rapidly advanced as a result of the continuously expanding newer age concepts on which CBCT is based upon. Apart from the advantage of minimal distortion, two-dimensional radiography in dental imaging like OPG (orthopantomogram) often is associated with superimpositions or distortions that are not captured in three-dimensional imaging of CBCT software. The user-friendly software of CBCT offers basic imaging and editing tools to the operator and helps them to observe the view of captured tissues in different modes. For example, CBCT software can be used to assess the tissues in multiplanar views, oblique slicing, curved slicing, and also in cross-sectional or oblique and coronal views. This multidimensional study is of the highest use to the dentist as morphologic characteristics, and the dimension of alveolar bone can be properly assessed prior to dental implant placement.
One more major application of CBCT software is that it enables the viewer to generate projections of the captured image virtually without any magnification or distortion. The volume visualization of the image is also done efficiently, thus excluding all gray values. Direct and indirect volume rendering functions are a part of all CBCT software for proper image assessment and manipulation to accuracy.
Over the course of the past 15 years, there are now numerous CBCT applications in many software formats that are helpful but not limited to dental diseases or anomalies like vertical root and dentin fractures, jaw tumors, prosthodontic evaluations, and advances in orthodontic or orthognathic and implant patient evaluations.
Mechanisms for surgical or prosthetic splint design and the CBCT scan data capacity to bridge with computer-aided design or manufacturing image files are useful for the fabrication of various dental restorations. CBCT is now a well-accepted diagnostic tool for the care of dental patients.
The ability of CBCT manufacturers to use various aspects of imaging technology in cost-effective and efficient practicality makes the numerous CBCT applications widely used in the imaging for nine different yet main branches of dental medicine ranging from implantation, oral surgery, and endodontics or root canal treatment. It facilitates implant and prosthodontic rehabilitation by synchronously planning and subsequently milling coronal restorations for teeth and root form implants.
The dentistry related applications also include;
Dentoalveolar abnormality detection in maxilla and mandible (upper or lower jaw), vertical root fractures, jaw tumors, dental cysts, and sinus infections.
For assessment of patients in orthodontic or orthognathic surgery.
Implant patient evaluations.
CBCT is the pioneer of dental three-dimensional imaging. Currently, it is used for a wide array of applications. The software is specially used for surgical and prosthodontic splint design. Its capability to scan data for the bridge with CAD (computer-aided-design)/CAM (computer-aided-manufacture)image files and for fabrication of various dental restorations makes it the most reliable technology at hand. As the demand for CBCT technology increases, so will the number of new applications for improved diagnostic techniques.