CBCT

Question 1

what structures can CBCT be used for

Answer 1

hard radiodense structures only e.g teeth and bone
useless for fat, muscle etc

Question 2

what reference line is used for CBCT and where should it be in a standing patient

Answer 2

frankfort plane parallel to the floor

Question 3

what shape is the x ray beam and the receptor in a CBCT

Answer 3

x ray beam: conical/pyramidal
receptor - square

Question 4

benefits to CBCT over plain radiography

Answer 4

no superimposition
ability to view subject from any angle
no magnification/ distortion
allows volumetric 3D reconstruction (not fully accurate)

Question 5

downsides of CBCT compared to plain radiography

Answer 5

increased radiation dose to the patient
lower spatial resolution (not as sharp)
susceptible to artefacts
equipment more expensive
images more complex to manipulate and interpret
requires additional training to justify, operate and interpret

Question 6

advantages of CBCT compared to CT

Answer 6

lower radiation dose
potential for sharper images
cheaper
smaller units

Question 7

advantages of CT compared to CBCT

Answer 7

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

Question 9

common used of CBCT in dentistry

Answer 9

clarifying relationship of M3M to ID canal prior to intervention
measuring alveolar bone dimensions to help plan implant placement
visualising complex root morphology to aid endodontic treatment
locating lost root in antrum

Question 10

name 3 common orthogonal planes used in dental CBCT

Answer 10

axial
sagittal
coronal

Question 11

what is the main drawback of utilising volumetric 3D reconstruction

Answer 11

modified reconstruction so can create misleading images
Particularly poor at showing thin bone - may show none at all

Question 12

name 3 examples of imaging variables that may be changed between CBCT scans

Answer 12

field of view
voxel size
acquisition time

Question 13

what is a voxel and how does voxel size impact CBCT images

Answer 13

voxel = 3D pixel
(never as small as intra oral pixels)
smaller voxels = clearer image however increased radiation dose and scan time

Question 14

roughly how much more radiation dose does a patient get from a CBCT compared to a panoramic

Answer 14

2-3x

Question 15

what are the 2 main artefacts seen on CBCT images

Answer 15

movement artefacts
streak artefacts

Question 16

what causes a movement artefact in a CBCT

Answer 16

patient not completely still during full exposure, affects whole scan

Question 17

what is a streak artefact in CBCT

Answer 17

most notable caused by high attenuation objects e.g amalgam and earrings
results in ‘lasers’ coming from attenuation object
Immediately adjacent to high attenuation object can appear very dark, should not be mistaken for caries

Question 18

contraindications to CBCT

Answer 18

plain radiograph is sufficient
pathology requiring soft tissue visualisation
high risk of debilitating artefacts e.g heaving restored dentition
patient factors - cant stay still e.g parkinsons

Question 19

what extra training must be done for CBCT

Answer 19

level 1 - for IRMER duty holders
level 2 - for those justifying, performing or interpreting