Cone beam computed tomography Flashcards
what is CT scanning?
Slices of tissue that can be stacked to produce a 3d image
compare the x-ray tube kV in dental machines to CT
much higher kV x-ray tube in CT than dental machines
what is the movement of a CT scan?
Axial movement -> spiral movement (hence called CAT scan)
in CT scanning the attenuation of the beam is measured by what?
detectors
in CT scanning
the patient is divided into ?
? assesses the radio-opacity of each one
Voxels
A computer
what is a voxel?
pixels with volume
what is used to give a quantitative measure of radio-density on CT scans?
Hounsfield scale
what Hounsfield number is given to air?
-1000
what Hounsfield number is given to water?
0
what Hounsfield number is given to cortical bone?
+1000
remember CT
uses of CT in the head and neck
Intracranial - bleed, infarction, tumour
Trauma
Evaluation of osseous lesion
Salivary glands
Neoplasia (benign/malignant) -
primary tumour / metastases
Orthognathic assessment and treatment planning
Implant planning
advantages of CT 3
No distortion/magnification like plain radiographs
Multiplanar - manipulate and reconstruct images
Quick like MRI
disadvantages of CT
High patient dose
Artefacts (metal objects e.g. amalgam)
May require IV contrast to distinguish tissues e.g. iodine - risk of reaction
Expensive
More difficult to interpret
this shows an amalgam artefact on CT
what is dentascan?
CT software available mainly for implants
compare cone beam CT to traditional CT?
X-ray tube rotates around the head capturing data with a cone-shaped x-ray instead of slices
lower radiation dose than medical CT
Still gives 3D image
what is taken prior to the CBCT scan to check the area of concern is in the field of view?
initial positioning view
CBCT - how image is acquired
X-ray tube and receptor ?
X-ray beam is ? shaped
Rotates ?* round patient
? sends information to ?
Initially a ? type image will appear on the PC screen
?? determines how the view can be modified
opposite
cone
360*
receptor
computer
DPT
imaging software
indications for CBCT use
developing dentition
- localisation of unerupted tooth
- Assessment of resorption from unerupted teeth
- Cleft palate patients
- Orthognathic surgery assessment
indications CBCT use in restorative dentistry
Few indications
Assess periapical lesions, root canal anatomy and perforations
Dental trauma
Dental anomalies
indications for CBCT use in surgery
Assessment of 3rd molars
Implant assessment
Jaw pathology assessment
TMJ bone surfaces
Facial fractures
what is the effective dose for Bitewing or periapical?
0.0003 - 0.022 mSv
what is the effective dose for DPT?
0.0027 - 0.038 mSv
what is the effective dose for lateral cephalogram?
0.0022 - 0.0056 mSv
what is the effective dose for upper occlusal radiographs?
0.008 mSv
what is the effective dose for CT head?
1.4 mSv
what is the effective dose for CT mandible and maxilla?
0.25 - 1.4 mSv
what is the effective dose for dento-alveolar CBCT?
0.01 - 0.67 mSv
what is the effective dose for craniofacial CBCT?
0.03 mSv
what affects the dose of an x-ray?
Manufacturer
Scan times
Volume size - field of view
Type of equipment
Part of maxillofacial region being imaged
advantages of CBCT
Multi-planar -> see image from all directions
Geometrically accurate images
Fast scanning times
Good spatial resolution
Lower radiation dose than medical CT
disadvantages of CBCT
Patient must be still
Soft tissues not imaged well
Radio-dense materials such as restorations produce beam hardening artefacts - streak artefacts
Images can be difficult to interpret
this is an I-CAT panoramic radiograph
this shows an I-CAT radiograph
remember
Additional training is required for CBCT
remember
Refer to guidance from European Academy Dentomaxillofacial Radiology
- Basic Principles for Basic Use of Dental Cone Beam CT
