other imaging modalities 2 Flashcards
other bony imaging options (bar plain films)
CBCT or CT
MRI (check changes in marrow)
CBCT
how it works
Low dose multi-planar imaging
Images made up from isotropic voxels
* Cubes of data with equal measurements
* Look at images in 3 planes (axial, coronal and sagittal)
* No distortion of images when looking in any plane
Good at bony imaging – Poor soft tissue contrast
what is 1
CBCT
condylar head
what is 2
CBCT
base of skull
what is 3
CBCT
frontal sinus
what is 4
CBCT
ethmoid and sphenoid sinus
what is 5
CBCT
pituitary fossa
options for size of CBCT
Large sagittal (17cm height) – for orthognathic surgery
smaller view (5cm) for isolated cysts and implant planning
CBCT vs CT
beam
CBCT - cone beam
CT - fan shaped beam
CBCT vs CT
dose
CBCT - low
CT - high
CBCT vs CT
soft tissue contrast
CBCT - poor soft tissue contrast
CT - good soft tissue contrast (windowing e.g. focus on bone alone or soft tissue with bone etc)
CBCT vs CT
radiographic contrast
CBCT - not needed
CT - can be used if indicated e.g. suspected malignancy
CBCT vs CT
pt position
CBCT - pt sitting upright/standing
CT - pt lying horizontally
CBCT vs CT
time
CBCT - quick/seconds
CT - long/3mins
dose comparision
IO variation - Child/adult/ tooth type/ digital/film
Variation – units doing, resolution of scan, full or half scan
Medical CT facial bone (approx. 8cm height)– mid range
indications for CBCT
4
Dental - impact teeth or implant planning
Bony anatomy – cysts, odontogenic tumours, ORN/MRONJ
indications for CBCT
4
Dental - impact teeth or implant planning
Bony anatomy – cysts, odontogenic tumours, ORN/MRONJ
investigations for this MRONJ/osteonecrosis case
Ill defined radiolucency around mental foramen seen on half OPT, there is a radiopacity within (possible sequestrum)
* need CBCT to investigate what it is and how close it is to mental foramen
Doesn’t look solid radiopaque mass – regions more radiolucent than others (moth eaten), irregular margins
* Mental foramen directly next to and perforates the lingual cortex
Differences in cancellous bone on either side
* Right side – very dark radiolucent cancellous bone – expect fatty marrow
* Any pt with chronic low grade inflammation get reactive sclerosis of bone
*
See sequestrum directly above IAN
investigations for this MRONJ/osteonecrosis case
Ill defined radiolucency around mental foramen seen on half OPT, there is a radiopacity within (possible sequestrum)
* need CBCT to investigate what it is and how close it is to mental foramen
Doesn’t look solid radiopaque mass – regions more radiolucent than others (moth eaten), irregular margins
* Mental foramen directly next to and perforates the lingual cortex
Differences in cancellous bone on either side
* Right side – very dark radiolucent cancellous bone – expect fatty marrow
* Any pt with chronic low grade inflammation get reactive sclerosis of bone
*
See sequestrum directly above IAN
what is needed to confirm dx osteomyelitis after this OPT
CBCT
Irregular radiolucency in mandible from 3-3, wide PDL and pus clinically (fits clinical expectation of osteomyelitis post extraction 42
CBCT for osteomyelitis characteristics
In axial view – see radiolucency and multiple sequestrations, perforation of lingual cortex – typical osteomyelitis appearance
In sagittal view – see extensions from crest to inferior border mandible
Perforations act as sinus tracts – create a periosteal reaction (not seen here, so acute here)
Chronic change – would see laminated thickening of cortical bone (periosteal change)
odontogenic lesions can be
2
cysts
tumours
Odontogenic lesion on OPT extending from 33 to 34, relatively well defined margin, sitting close to mental foramen
* CBCT needed for biopsy and surgical planning
odontogenic lesions on CBCT
Axial view – see ovoid radiolucent lesion, slight expansion buccal but both cortical plates intact
higher vertical dimension than axial view
when do we do TMJ imaging
Myofascial
No imaging required
Internal derangement (clicks/cracks/limitation)
* MRI is gold standard
* Ultrasound is alternative – controversial, if not suitable for MRI
Degenerative
* CBCT
MRI for TMJ
internal derangement (clicks/cracks/limitation)
US is alternative but controvesial (only if pt not suitable for MRI)
KEY
* T1W scan fat is always white, bone is black and fluid is black – good for anatomy
* T2W scan fat is white, fluid is white, bone is black – good for pathology
So CSF can determine
MRI for internal derangement for TMJ looks at
Disc is visualised on MRI (only one that can see properly)
Can determine if with or without reduction and which direction the disc moves in relation to the condyle.
* 2 views to determine displacement (medial and/or lateral)
Need to view in para-sagittal (along short axis of condyle) and para-coronal (along long axis of condyle)
* Need dedicated TMJ MRI, not a typically head or neck view
describe these TMJ MRIs
T1W parasagittal view (fat is white)
Usually healthy articular disc – bow tie shape, usually sits at 12 to 10 o’clock
First is normal healthy TMJ joint and articular disc
Image the pt closed and open – 2nd image is open – codylar head has translated forward (normal again)
3rd -abnormal, advanced osteoarthritic appearance – thinning of cortical bone on superior surface (not equal thickness all way round), loss of joint space, fatty marrow is no longer bright white in condylar head – suggested inflammation and degeration. Disc isn’t in normal position – sitting anteriorly beneath articular eminence, shape is smaller and no longer bow tie (shrivelled and desiccated) – long standing articular inflammatory reaction
**Anterior disc displacement without reduction **
imaging for degenerative change of TMJ
Supplement MRI with CBCT – see bone in more detail
See osseous changes more detail
Left image is right degenerative TMJ, right image is left healthy TMJ
Degenerative - irregularities, no smooth outlines, osteophyte at edge (beak) – all degenerative change from osteoarthritis – early stage
how to assess facial assymmetry with imaging
initially US and noticed discrepanacy in floor of mouth
OPT done and noticed left condyle was large compared to right, chin point deviation
CBCT to get more detail
* Left side is bigger than pt right
* Condylar head not sitting in joint space, reaching towards anterior aspect of articular eminence (parasagittal view)
* See subtle change in density in condylar head
Either condylar hyperplasia or osteoblastoma or fibrous dysplasia
Biopsy after MRI
* Condylar hyperplasia – had distraction osteogenesis
when is Radionuclide (SPECT singular positron electron CT) used
E.g Condylar hyperplasia – is joint undergoing active growth?
99mTc used
**Check for activity of joint compared to normal **
High sensitivity, low specificity (cannot tell why – tumor, infection, hyperplasia)
Only used as screening method to see if there is more activity
Not really used due to increased radiation exposure
process of imaging for H&N oncology
Following examination and history taking:
Cross-sectional imaging with contrast (depending on type of tumor)
* CT (SCC)
* MRI
Extensive imaging as assessing distant metastases – e.g. suspect in tongue do head, neck and thorax
Ultrasound guided biopsy of cervical lymphadenopathy
PET/CT – if cannot find primary tumour
DPT for Dental assessment prior to radiotherapy
benefit of CT scan with contrast for H&N oncology
tumors light up with contrast
Darker areas are geniohyoid and mylohyoid
See cervical lymph node in level 1b (circle), enlarged – likely local metastatic spread
why would an MRI with contrast be used for H&N oncology over CT with contrast
Better definition of tumour compared to CT
* See lingual septum is getting encroached on by tumour
* Could change tx plan as getting to contralateral side
but takes longer and more contraindications for MRI
CT with contrast vs MRI with contrast
for H&N oncology
MRI
* no radiation dose to the patient
* scan takes longer
* More contraindications for MRI: Pacemakers, cochlear implants, metal in tattoo (heatup), Claustrophobic
CT
* only contraindication is allergy to iodine-based contrast - rare
but MRI better for assessing (better definition)
* perineural spread
* Bone invasion via bone marrow changes
* soft tissue characteristics of lesion
describe this image
was a level2 mass on neck (firm and fixed)
US
Benign – smooth, lobulated – able to draw round
Here cannot draw round - MALIGNANT
Check masses relationship with CCA and internal jugular vein for level 2 and 3 of neck – here encased
Extracapsular spread here – prognostic 50% worse
Pt went on to have CT found oropharyngeal base of tongue tumor and metastatic spread through perineural invasion to both sides neck and intracranial spread
Necrotic cystic lump further down neck also found –US biopsy non necrotic area to assess
what is PET
Positron Emission Tomography
Radioactive fluorine labelled glucose injected (18 – FDG)
* Goes to metabolically active tissues
* Doesn’t give anatomical detail so overlaid onto CT or MRI
* Good for looking for unknown primary tumours
* Useful for follow-up and recurrence
Goes to any metabolic active tissue – not allowed to talk or drink or swallow
