Other Imaging Modalities 2

Question 1

What is used following plain film when imaging bony tissues?

Answer 1

CBCT- good for cortical bone and dentition

CT- shows soft tissues

MRI- marrow changes, osteomyelitis, peri-neural spread

Question 2

What are the features of CBCT?

Answer 2

Low dose multi-planar imaging- gives reconstruction

Images are made of isotropic voxels (like pixels)

Question 3

What are isotropic voxels?

Answer 3

– Cubes of data with equal measurements (height, width, depth)
– Look at images in 3 planes (axial, coronal and sagittal)
– No distortion of images when looking in any plane
- Smaller voxels = better resolution of image

Question 4

What is the issue with CBCTs poor contrast of soft tissue?

Answer 4

May only show outlines of ST
-> will not show pathology
-> muscles appear pale grey but cannot see definition

Question 5

How is CBCT similar to OPT?

Answer 5

Similar positioning

Panel and source move in opposite directions around patient

Question 6

What are the differences between CBCT and CT?

Answer 6

Beam:
CBCT- cone shaped
CT- fan shaped

Dose:
CBCT- low
CT- high

ST contrast:
CBCT- poor
CT- good (windowing possible- can focus more on bone or ST)

Radiographic contrast:
CBCT- not required
CT- required (usually IV)

Positioning:
CBCT- sitting upright or standing
CT- lying down

Timing:
CBCT- 9 secs
CT- 3-5mins

Question 7

Effective dose comparison of different imaging modalities in uSV?

Answer 7

IO: 0.3-21.6

OPT: 2.7-38

CBCT (up to 5cm): 11-214

*CBCT (5-10cm): 18-674

CBCT (over 15cm): 30-1025

*CT facial bone/maxilla: 430-860

*comparable

Question 8

What are the different fields of view sizes in CBCT and their use?

Answer 8

Smallest is 5cm- imaging of teeth/cysts, implant planning

Largest is 17cm- used for orthognathic surgery

Question 9

What causes variation in effective dose in image modalities?

Answer 9

OPT/IO- speed of film, wet or digital

CBCT/CT- voxel dose, whether 180 (children)/360

Question 10

What is the most common reason for using CBCT?

Answer 10

Determining orientation of impacted teeth

Implant planning

Cysts

Tumours

ORN

MRONJ

Osteomyelitis

Question 11

Why is CBCT helpful for identifying sequestrum?

Answer 11

Can determine whether radiolucency seen on OPT is a sequestrum

Can localise it for surgical planning

Question 12

How does MRONJ appear on CBCT?

Answer 12

Moth eaten appearance of mandible

Perforation of lingual cortex

Sclerosis of bone- reaction to inflammatory stimulus

Question 13

What are the signs which help confirm diagnosis of osteomyelitis Clinically, on OPT and using CBCT?

Answer 13

Clinically- pus

OPT- wide PDL, large/multiple radiolucency

CBCT
-> perforation of cortex- may act as sinus tract
-> sequestration
-> if chronic- laminated thickening of cortical bone
-> speckled radiopacities

Question 14

How do odontogenic cystic lesions or tumours appear on OPT and CBCT?

Answer 14

 OPT- large radiolucency, well defined margins

 CBCT- ovoid lesion, cortical plates intact (may be thinned), larger vertical dimension (so look at 3 views)

Question 15

Why is CBCT so useful for locating odontogenic lesions and tumours?

Answer 15

Helps plan surgery- can see proximity of nerves and other vital structure in relation to growth

Question 16

Which types of imaging is used for different types of TMD?

Answer 16

Myofascial pain- no imaging

Internal derangement- MRI or ultrasound

Degenerative (if crepitus/history of athritis)- CBCT

Question 17

What are the differences between T1 and T2 MRIs?

Answer 17

 T1 weighted scan- fat is white, bone is black, and fluid is black (good for anatomy)

 T2 weighted- fat is white, fluid will be white, bone remains black (look at CSF of brain)
-> T2 is good for pathology

Question 18

Why is MRI helpful in TMD cases with internal derangement?

Answer 18

 Disc is visualised on MRI- appear bowtie shaped and dark grey (10 to 12 position)

 Can determine if with or without reduction and which direction the disc moves in relation to the condyle

Question 19

Why are para-sagittal (along short axis of condyle) and para-coronal (along long axis of condyle) views required in MRI of internal derangement of TMJ?

Answer 19

As anterior displacement may also be medial or laterally

Question 20

Why when imaging the TMJ is it done opened and closed?

Answer 20

To visualise how disc translates

Question 21

What are the features of an abnormal TMJ (due to OA) on opening on MRI?

Answer 21

 Thinning of cortical bone
 Loss of joint space
 Fatty marrow is no longer bright (inflammation and degeneration)
 Disc- sitting further anterior, smaller, loss of bow tie shape, desiccated

-> supplement with CBCT if you want to see bone better

Question 22

What are the features of a CBCT showing TMJ suffering from OA?

Answer 22

Presence of osteophytes (sharp beaks)

Ragged appearance

Lack of joint space

Question 23

What can cause facial asymmetry in TMJ area?

Answer 23

Condylar hyperplasia

Question 24

How can CBCT be used in condylar hyperplasia?

Answer 24

To confirm diagnosis
-> can show one condyle is bigger (axial plane)
-> can show position of condyle in joint space (para-sagittal plane)

Question 25

What treatment can be used to fix condylar hyperplasia?

Answer 25

Distraction osteogenesis

Question 26

What does SPECT stand for? What is it?

Answer 26

Single-photon emission computerised tomography (nuclear medicine using 99mTc)
-> checks for metabolic activity within joint
-> more uptake = more activity

Question 27

What are the advantages/disadvantages of SPECT?

Answer 27

ADV:
Very sensitive to increased activity
-> good at picking up tumours, infection, inflammation and growth
Good for picking up condylar hyperplasia

DIS:
Low specificity- broad spectrum
Only used as screening method

Question 28

What imaging techniques are used in Head and Neck Oncology following examination and history taking?

Answer 28

 Cross-sectional imaging with contrast
– CT
– MRI

 Ultrasound guided biopsy of cervical lymphadenopathy

 PET/CT

 DPT for Dental assessment prior to radiotherapy

Question 29

What are the advantages of MRI compared to CT?

Answer 29

MRI has no radiation

MRI is better for assessing:
-> perineurial spread
-> bone invasion via marrow changes
-> soft tissue characteristics of lesions

Question 30

What are the disadvantages of MRI compared to CT?

Answer 30

MRI takes longer- up to 45mins- 1hr

Pacemakers and cochlear implants are contraindicated due to strong magnet

Tattoos and make up contain metal particles and can heat up during scan

CT may make it easier to see tumour and enlarged LNs

Question 31

What imaging may be helpful in assessing lumps in neck?

Answer 31

Ultrasound- esp if firm and getting bigger
-> if not encapsulated it suggests it may be malignant

Question 32

What is the issue with malignancy in the neck?

Answer 32

Necrotic neoplastic mass can envelop blood vessels
-> spread easier

Question 33

Which part of a necrotic SSC in neck node should you biopsy?

Answer 33

Solid portion (most of it will be fluid filled)

Question 34

What is PET?

Answer 34

Positron Emission Tomography
-> type of nuclear medicine

Question 35

When is PET considered

Answer 35

If not able to find primary tumour with CT etc
-> PET shows hotspots of activity

For follow up and screening against recurrence

Question 36

How does PET work?

Answer 36

 Radioactive fluorine labelled glucose injected (18 – FDG)

 Goes to metabolically active tissues- areas where glucose is required and used (such as tumours)

 Doesn’t give anatomical detail so overlaid onto CT or MRI

Question 37

Why is it important that the patient does not talk or move too much when PET contrast is in place?

Answer 37

Material goes to any metabolically active tissue
-> if muscles in area are activated it can disturb scan as these will present as hotspots