Other Imaging Modalities 2 Flashcards
What is used following plain film when imaging bony tissues?
CBCT- good for cortical bone and dentition
CT- shows soft tissues
MRI- marrow changes, osteomyelitis, peri-neural spread
What are the features of CBCT?
Low dose multi-planar imaging- gives reconstruction
Images are made of isotropic voxels (like pixels)
What are isotropic voxels?
– 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
What is the issue with CBCTs poor contrast of soft tissue?
May only show outlines of ST
-> will not show pathology
-> muscles appear pale grey but cannot see definition
How is CBCT similar to OPT?
Similar positioning
Panel and source move in opposite directions around patient
What are the differences between CBCT and CT?
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
Effective dose comparison of different imaging modalities in uSV?
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
What are the different fields of view sizes in CBCT and their use?
Smallest is 5cm- imaging of teeth/cysts, implant planning
Largest is 17cm- used for orthognathic surgery
What causes variation in effective dose in image modalities?
OPT/IO- speed of film, wet or digital
CBCT/CT- voxel dose, whether 180 (children)/360
What is the most common reason for using CBCT?
Determining orientation of impacted teeth
Implant planning
Cysts
Tumours
ORN
MRONJ
Osteomyelitis
Why is CBCT helpful for identifying sequestrum?
Can determine whether radiolucency seen on OPT is a sequestrum
Can localise it for surgical planning
How does MRONJ appear on CBCT?
Moth eaten appearance of mandible
Perforation of lingual cortex
Sclerosis of bone- reaction to inflammatory stimulus
What are the signs which help confirm diagnosis of osteomyelitis Clinically, on OPT and using CBCT?
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
How do odontogenic cystic lesions or tumours appear on OPT and CBCT?
OPT- large radiolucency, well defined margins
CBCT- ovoid lesion, cortical plates intact (may be thinned), larger vertical dimension (so look at 3 views)
Why is CBCT so useful for locating odontogenic lesions and tumours?
Helps plan surgery- can see proximity of nerves and other vital structure in relation to growth
Which types of imaging is used for different types of TMD?
Myofascial pain- no imaging
Internal derangement- MRI or ultrasound
Degenerative (if crepitus/history of athritis)- CBCT
What are the differences between T1 and T2 MRIs?
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
Why is MRI helpful in TMD cases with internal derangement?
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
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?
As anterior displacement may also be medial or laterally
Why when imaging the TMJ is it done opened and closed?
To visualise how disc translates
What are the features of an abnormal TMJ (due to OA) on opening on MRI?
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
What are the features of a CBCT showing TMJ suffering from OA?
Presence of osteophytes (sharp beaks)
Ragged appearance
Lack of joint space
What can cause facial asymmetry in TMJ area?
Condylar hyperplasia
How can CBCT be used in condylar hyperplasia?
To confirm diagnosis
-> can show one condyle is bigger (axial plane)
-> can show position of condyle in joint space (para-sagittal plane)
What treatment can be used to fix condylar hyperplasia?
Distraction osteogenesis
What does SPECT stand for? What is it?
Single-photon emission computerised tomography (nuclear medicine using 99mTc)
-> checks for metabolic activity within joint
-> more uptake = more activity
What are the advantages/disadvantages of SPECT?
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
What imaging techniques are used in Head and Neck Oncology following examination and history taking?
Cross-sectional imaging with contrast
– CT
– MRI
Ultrasound guided biopsy of cervical lymphadenopathy
PET/CT
DPT for Dental assessment prior to radiotherapy
What are the advantages of MRI compared to CT?
MRI has no radiation
MRI is better for assessing:
-> perineurial spread
-> bone invasion via marrow changes
-> soft tissue characteristics of lesions
What are the disadvantages of MRI compared to CT?
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
What imaging may be helpful in assessing lumps in neck?
Ultrasound- esp if firm and getting bigger
-> if not encapsulated it suggests it may be malignant
What is the issue with malignancy in the neck?
Necrotic neoplastic mass can envelop blood vessels
-> spread easier
Which part of a necrotic SSC in neck node should you biopsy?
Solid portion (most of it will be fluid filled)
What is PET?
Positron Emission Tomography
-> type of nuclear medicine
When is PET considered
If not able to find primary tumour with CT etc
-> PET shows hotspots of activity
For follow up and screening against recurrence
How does PET work?
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
Why is it important that the patient does not talk or move too much when PET contrast is in place?
Material goes to any metabolically active tissue
-> if muscles in area are activated it can disturb scan as these will present as hotspots
