CBCT Imaging and Computed Tomography Quiz

Computed Tomography and Cone Beam CT

• Computed tomography (CT) creates 3D images.
• CT uses physical principles to create images.
• Image creation involves windowing of the grayscale.
• Planar (2D) imaging uses a stationary X-ray source and sensor.
• Planar imaging projects all structures in the beam path onto a flat plane on the receptor.
• Structures overlap in planar imaging, making it impossible to visualize tissues at different layers.
• Posterior-anterior skull radiographs are an example of planar imaging.
• CT imaging involves rotating the X-ray source and sensor around the body.
• Hundreds of exposures are made from diverse angles during CT imaging.
• Absorption, transmission, and scatter patterns are generated as the beam circles the structures.
• A computer records each exposure to create a 3D array of data.
• Separating structures from different angles eliminates overlap in the image.
• Computed tomography utilizes multiple views of an object at different angular orientations.
• Overlapping structures are eliminated, enabling differentiation of tissues.
• Planar (2D) imaging flattens all structures onto a plane.
• CT (3D) imaging separates structures, enabling separate depiction of each structure.
• An X-ray beam is confined to a narrow fan shape in CT imaging.
• This results in the production of numerous sections (slices).
• Recording exposures in each section is done by a computer.
• The term "Computed Tomography" is used to indicate this process.
• The computer receives data from hundreds of basic images of the tissue section.
• Varying projection angles lead to different patterns of x-ray absorption in the tissue.
• Computers use data to divide tissue sections into thousands of blocks called voxels.
• CT numbers (Hounsfield Numbers) are assigned to each voxel, correlating with X-ray absorption.
• CT numbers vary across tissues.
• Air has approx. -1000 HU, water is 0 HU
• Bone has approx. +1000 HU, metal is approx. +3000 HU
• Pixels represent voxels in CT images, with each pixel assigned a CT number generated from the voxel.
• Gray shades are assigned to pixels based on their CT numbers, creating image contrast.
• Lower CT Numbers correspond to darker shades.
• Higher CT Numbers create lighter shades.
• Intraoral digital radiology utilizes a similar principle.
• A range of 256 shades are used to show different tissues in the image.
• Applying this to 4000 CT numbers leads to insufficient shades which reduces contrast.
• Windowing is done to limit imaging to specific CT ranges, enhancing contrast and visualization.
• Using windowing helps show subtle differences in soft tissues while hard tissues receive consistent shades.
• Using windowing makes it possible to visualize areas with low CT numbers - soft tissues.
• Using windowing makes it possible to visualize areas with high CT numbers - bone.
• Cone beam computed tomography (CBCT) is a modification of traditional computed tomography.
• CBCT was developed in the 1980s for angiography.
• CBCT shares some similarities with CT, but with important distinctions.
• CBCT creates views of the cranium and maxillofacial complex in three planes of space.
• It effectively removes overlapping structures.
• Images possess minimal distortion and magnification.
• Capturing CBCT images involves X-ray generation and detection.
• Reconstruction involves building the image using voxels and pixels.
• Images are formatted using gray scale and multiplanar reformatting.
• The process results in a 3D presentation viewable on a screen.
• A conical X-ray beam and detector rotate around the patient's head in CBCT imaging.
• Approximately 400 basis images are collected from different angles.
• The complete series of basis images creates the projection data.
• Image data is often captured through a flat panel detector.
• The number of basis images is influenced by factors like frame rate (exposures/second), rotation path, and rotation speed.
• CBCT typically produces one basis image per degree of rotation.
• The difference between CBCT and CT lies in beam size (cone-shaped vs. fan-shaped).
• CBCTs field of view (FOV) can range from a small area of the jaws to the entire head.
• Some CBCT units allow smaller FOVs.
• CBCT can be collimated to reduce the FOV size.
• The FOV should be selected based on the intended procedure.
• CBCT reconstruction involves dividing data into numerous 3-D voxels, maintaining consistent size in all orientations.
• Voxel size is dependent on the detector matrix.
• Voxels in CBCT are smaller compared to CT voxels.
• Smaller voxels result in sharper images.
• The image’s data set can be reconstructed with voxel sizes that are different from acquired sizes.
• The spatial resolution capabilities of the imaging system are critical for distinguishing closely spaced items.
• The spatial resolution is measured in line pairs per millimeter.
• Voxel size is a contributing factor in determining resolution but is not synonymous with resolution itself.
• CBCT resolution depends on detector pixel size, beam projection geometry, detector and patient movement, and radiation scattering.
• Each voxel is represented by a 2-D pixel.
• CBCT images consist of thousands of small square pixels.
• Each pixel is assigned a gray level that reflects X-ray absorption.
• Higher X-ray absorption results in lighter colors/shades and vice-versa.
• Bit depth (number of possible gray shades) typically is 8-bit (256).
• Appropriate gray shades are needed for image contrast.
• “HU” tools may appear but they are not standardized HU values.
• Determining the best exposure parameters for patients accounts for factors like exposure settings, FOV, voxel/pixel size, and resolution.
• Orthodontics and implant procedures often require larger FOV for multiple site visualization.
• A larger FOV results in higher radiation dose, but enhances the desired anatomy visualization.
• Larger FOV leads to larger voxel/pixel sizes, reducing spatial resolution although this is not usually a concern with pixel sizes below 0.4 mm.
• CBCT visualization of abnormalities/TMJs uses a medium FOV, balancing radiation dose and resolution requirements.
• Endodontic applications benefit from a small FOV for limited exposure and smaller pixel sizes to enhance resolution.
• Smaller FOV for endodontic applications needs good exposure values to overcome noise.
• CBCT data is displayed with multiplanar reformatting (axial, sagittal, coronal).
• The data can be scrolled through to inspect all planes in the entire thickness.
• CBCT utilizes non-orthogonal configurations, including curved planar views that are aligned with the long axis of the dental arch.
• These formats generate panoramic-like and serial transplanar views (cross-sectional).
•   CBCT includes volume presentation through 3D surface rendering.
• Shading in 3-D surface rendering represents the outer surface of tissues enabling better distinction of buccal-lingual structures, thus enhancing diagnoses of bony abnormalities on surfaces.
• Artifacts in CBCT include scattered radiation (grainy or streaky appearance), partial volume averaging (resulting in step/blurred edges), beam hardening (dark areas beside radiopaque material or creating lines/streaks), and procedure-related issues (e.g. ring artifact from miscalibrated detectors or patient movement).