RADIOLOGY - CBCT

Question 1

what is a CBCT?

Answer 1

a form of cross-sectional imaging suitable for assessing radiodense structures

Question 2

what are the non-DMFR uses of CBCTs?

Answer 2

temporal bone imaging
paranasal sinus imaging
orthopaedic imaging
radiotherapy planning

Question 3

what shape is the cbct xray beam?

Answer 3

conical/ pyramidal

Question 4

how are cbcts formed?

Answer 4

conical/ pyramidal xray beam and square digital detector rotate around head (no more than 1 full rotation)
capture many 2D images which are reconstructed into a cylindrical 3D image

Question 5

what position is the patient in for a cbct?

Answer 5

usually either standing or sitting
head position same as panoramic (frankfort plane and sagittal plane aligned)

Question 6

what are the benefits of cbct over plain radiography?

Answer 6

no superimposition
ability to view subject from any angle
no magnification/ distortion
allows for volumetric (3D) reconstruction

Question 7

what are the downsides to cbct over plain radiography?

Answer 7

increased radiation dose to patient
lower resolution (not as sharp)
equipment more expensive
imaged are more complicated to manipulate and interpret

Question 8

what are the benefits of CBCT over conventional CT?

Answer 8

lower radiation dose
potential for sharper images
cheaper
smaller footprint

Question 9

what are the benefits of conventional CT over CBCT?

Answer 9

able to differentiate soft tissues better
cleaner images
larger field of view possible

Question 10

what are the common uses of CBCT in dentistry?

Answer 10

clarifying the relationship between impacted 8s and IDC after plain radiograph suggested possible
measuring alveolar bone dimensions to help plan implant placement
visualising complex root canal morphology to aid endodontic treatment
investigating external root resorption next to impacted teeth
assessing large cystic jaw lesions and their involvement of important anatomical stuctures

Question 11

what are the common orthogonal planes in cbct?

Answer 11

axial
sagittal
coronal

Question 12

what is altered on the cbct machine before the scan starts?

Answer 12

field of view
voxel size
acquisition time

Question 13

what is the field of view in cbct?

Answer 13

the size of the captured volume of data

Question 14

what is a voxel?

Answer 14

3D pixel

Question 15

what does a decrease in voxel size lead to?

Answer 15

increased radiation dose

Question 16

what is the dose of a CBCT compared to a panoramic radiograph?

Answer 16

CBCT 2-3x the dose of a panoramic

Question 17

what are artefacts on a cbct?

Answer 17

visualised structures on the scan that were not present in the object investigated

movement artefacts
streak artefacts

Question 18

how does a movement artefact arise in a cbct? and how does it present?

Answer 18

if patient not still
presents as blurriness or extra contours

Question 19

what are streak artefacts on a cbct caused by? and what issues can arise from this?

Answer 19

caused by high-attenuation objects like amalgam
can prevent caries assessment and canals in root treated teeth

Question 20

what are contraindications for cbct?

Answer 20

if plain radiographs are sufficient
pathology requiring soft tissue visualisation e.g., malignancy, infection in soft tissue
if high risk of debilitating artefacts
patient factors - cant stay still or fit in the machine