CBCT PDF

Oral Radiology CBCT OMD-725  CBCT It is a recent imaging technique accomplished by a cone-shaped X-ray beam and a 2 dimensional detector area that rotate around the patient to acquire multiple 2D images  CBCT The raw digital data i...

Oral Radiology CBCT OMD-725  CBCT It is a recent imaging technique accomplished by a cone-shaped X-ray beam and a 2 dimensional detector area that rotate around the patient to acquire multiple 2D images  CBCT The raw digital data is composed of multiple images resembling lateral ceph. each slightly offset from one another. This data is reconstructed by computer algorithm to create volumetric data.  CBCT Multiple projections are acquired by rotational scanning to produce volumetric data from which multi-planar images can be generated.  CBCT The computer then collect the information into tiny cubed or voxels (typically 0.4 mm x 0.4mm ). Individual voxels are much smaller than in medical CT. The voxel sizes in newer machines are even smaller (0.15mm x 0.15mm x 0.15 mm) so improving image resolution CBCT Example of CBCT unit. Imaging may be performed with the patient seated, supine, or standing. The patient’s head is positioned and stabilized between the x-ray generator and detector by a head-holding apparatus. The detector may be a flat panel or image intensifier. During exposure, the generator and detector rotate fully or partially around the patient’s head. Scan time may be as fast as 5 seconds.  CBCT patient positioning 1- Sitting: – Most comfortable – Fixed seats are not easily accessible for patients on wheel chairs  CBCT patient positioning 2- Standing: – Height may not be adjusted to accommodate patients on wheel chairs  CBCT patient positioning 3- Supine: – Occupy large area – Not easy for patients with physical disabilities  Image display The volumetric data is presented on the computer screen as secondary images in three orthogonal planes (axial, sagittal , and coronal ) as well as 3D images Image display  CT CBCT Fan shaped x-ray beam. Cone shaped x-ray beam. Slit collimation. Cone collimation. Linear detector. Area detector(flat panel). Multiple rotations. Single rotation. Rectangular voxel. Cuboid(isotropic) voxel. Bone & soft tissue Only bone examination. examination. No software provided. Software provided.  CONVENTIONAL CT X-ray source Fan’ of X-rays Detector  CBCT/CBVT X-ray source Cone’ of X-rays Detector Detector  CBCT CT X-ray beam X-ray beam is cone- X-ray beam is fan- shaped (3D) shaped (2D) Detector Uses a (2D) digital array Uses a (linear) detector detector  CBCT CT ROI The entire ROI is Only possible in MDCT scanned in one rotation Voxels Have isotropic voxels Only in MDCT  Over CT ,CBCT provides also reformatted panoramic cuts, trans-axial( cross section cuts)  CBCT Special detector Image intensifier tube/ Charged couple device (IIT/ CCD) Flat panel detectors Flat panel detectors have high resolution and inexpensive, but they require more radiation  Fields of view FOV FOV depend on: Detector size and shape Collimation of 1ry x- ray beam The larger the FOV the larger the voxel size, the lower the resolution. Large FOV Medium FOV Focused FOV Focused (Stitched) FOV  CBCT Field of View Scanning the entire cranio-facial region is difficult because of high cost of large detectors. Possible to increase the height of the FOV by using 2 scans one above the other and (stitching) the data.  CBCT Multi-planar Reconstruction Since the volumetric data is isotropic, means having properties that are identical in all directions Thus, data can be sectioned non-orthogonally (e.g. oblique, curved planar).  Advantages of CBCT Less radiation dose to the patients than CT (96 to 51% of CT) Less expensive equipment than CT Smaller in size than CT Less scanning time than CT because it captures the necessary data in one rotation  Advantages of CBCT Reformatted images can generate – Panoramic – Lateral cephalometric – PA cephalometric – Submentovertex  Advantages of CBCT Sagittal, coronal and axial images appear simultaneously on the computer monitor Selecting and moving the cursor lines on one image automatically alters the other reconstructed images.  Advantages of CBCT Sub-millimeter voxel resolution (0.4x0.4x0.4mm - 0.125x0.125x0.125mm). One scan contains more than 100 million voxels. Some CBCT units are capable of high-resolution imaging (0.076- to 0.125-mm voxel resolution) Interactive analysis for surgeries and implants  Disadvantages of CBCT Poor soft tissue contrast (TMJ disc cannot be seen) Patients have to remain stationary Computer reconstructed panoramic images are not directly comparable with conventional panoramic radiographs. Metallic objects produce streak artifacts.  Application of CBCT in Dental field Dental Implant Maxillofacial surgery Tempromandibular joint Orthodontics Disease Cleft palate Endodontic application  Dental implants CBCT, combined with customized software, provide the necessary 3-D information. This allows determination of the optimal implant size and location considering surgical, anatomic, and prosthodontic issues.  Dental implants Stereolythographic (3D printing) models of the jaws as well as surgical guides. Such models of the facial bones are used for pre-surgical treatment planning The surgical guides assist the clinician in precisely aligning the drill bits with respect to the jaw bones to assure proper orientation and depth of the drill holes.  Surgical conditions of the maxillofacial complex CBCT delineate the location, size and extension of intra bony lesion. This will give surgeon the needed information for surgical planning with ability to provide volumetric analysis of the case.  Tempromandibular joints The TMJ is difficult to image with conventional techniques because of superimposition. CBCT provided valuable images of the osseous components of the TMJ such as osteophytes, erosion, fractures, ankylosis, or developmental abnormalities, as well as to evaluate the position of the condyle in the fossa in open- mouthed and closed-mouth positions.  Temporomandibular joint: (a) corrected lateral and (b) frontal views demonstrating smooth cortical outlines of the mandibular condyle and mandibular fossa of temporal bone. The position of the condyle within the fossa, concentric, is normal. Images made with the 3DX Accuitomo (J. Morita USA., Inc., 9 Mason, Irvine, CA).  Orthodontics CBCT providing 2D and 3D cephalometric images which is more accurate than conventional 2D cephalometric radiographs ( no magnification or parallax distortion). Distortion free panoramic reformatted image can be held without re expose the patient.  Orthodontics Pharyngeal air way space and soft tissue relationship can be provided by CBCT. CBCT can detect teeth impaction easily. Disease  Ameloblastoma. An 18-year-old male. Data acquired using an iCAT CBCT machine. Images are reformatted in OnDemand 3-D, a third-party software. (a) Sagittal view of the right mandible showing a large multilocular lesion and inferior displacement of the third molar. (b) Coronal section through the angle of the mandible. Compared to the normal left side, the right side shows expansion in buccolingual aspect and lower border of the mandible. The third molar is next to the buccal cortical plate. (c) A 3-D reconstruction of the involved area, showing the thinning and perforation of the cortical plates. The superimposing structures (vertebra, hyoid bone) are subtracted by segmentation.  Cleft palate CBCT showed 3D relations of the defect and bone thickness around the existing teeth in proximity to the cleft. The volume of the graft material needed for repair could be estimated by volumetric analysis.  Endodontic application Diagnosis of endodontic pathosis Canal morphology Assessment of pathosis of non-endodontic origin Evaluation of root fractures and trauma Analysis of external and internal root resorption and invasive cervical resorption Pre-surgical planning Canal morphology  Diagnosis of endodontic pathosis and assessment of pathosis of non-endodontic origin Evaluation of root fractures and trauma Analysis of external and internal root resorption and invasive cervical resorption Pre-surgical planning  CBCT Artifacts 1-BeamHardening Artifact (Streak artifact) – Because of absorption of the X-ray beam by metal objects – Avoided by: Reduce FOV Separate the dental arches  CBCT Artifacts 2- Patient movement Un-sharpness of the reconstructed images 3- Circular (ring) artifact – Poor calibration of detectors. – Using a smaller flat panel with the source-detector axis positioned offset to the center of rotation can result in ring artifacts.  Circular (ring) artifact Solution: Recalibrating the detector is sufficient to fix this artifact. a) Coronal and (b) sagittal views showing white ring artifacts (black arrow)  Faculty of Dentistry