oncology and bony imaging Flashcards
what is used for bony imaging?
CBCT/CT
- superior for visualising cortical bone changes
MRI to check for changes in marrow pattern
- inflammation/neoplasia
CBCT
low dose multiplanar imaging
images made up from isotropic voxels (pixels)
look at images in 3 planes - axial, coronal, sagittal
no distortion of images when looking in any plane
good at hard tissue - bony imaging
- poor ST contrast
CBCT smaller voxel =
higher resolution
CBCT isotropic
equal measurements in all directions - height, width, depth
cubes of data with equal measurements
how is CBCT taken?
pt stands/sits in centre of unit head still - chin rest or head strap xray source - cone shaped beam flat panel detector = rotate 180 or 360 degrees in opp direction
interpreting CBCT
cortical bone white
air black
ST grey - difficult to distinguish from SC fat
comparing CT and CBCT - beam
CBCT cone shaped
CT fan shaped
comparing CT and CBCT - dose
CBCT low
CT high
comparing CT and CBCT - contrast
CBCT none
CT use of iodinated for ST
comparing CT and CBCT - positioning
CBCT - upright seated/standing
CT - horizontal
uses of CBCT
ORN/MRONJ - moth eaten appearance - precisely locate sequestra osteomyelitis - moth eaten appearance further investigation of odontogenic lesions - cysts and tumours
TMJ imaging - myofascial (parafct habits)
no imaging required
give conservative advice
TMJ imaging - internal derangement
MRI gold standard
- can visualise disc
- parasagittal and paracoronal planes
US alternative e.g. if pt is claustrophobic, articular disc not visualised in US
TMJ imaging - degenerative - osteoarthritis/RA
CBCT / (CT)
loss of uniformly thick cortical bone
osteophyte - projection of new bone
thinning and erosion
facial asymmetry
condylar head different trabecular pattern in part could suggest neoplastic change
how does MRI work?
protons - spin creating small magnetic charge
when a strong magnetic field is introduced protons align with that field
technician introduces a radio frequency pulse
disrupts proton and forces it into 90/180 degree realignment with static magnetic field
- radiofrequency pulse pushes it against its nature
when pulse is turned off protons realign with magnetic field - release EM energy
MRI detects this energy and differentiates various tissues based on how quickly they release energy after pulse is turned off
T1W MRI
good for anatomy
fat white
cortical bone black
fluid and air black
T21 MRI
fat and fluid white
TMJ imaging - radionucleotide SPECT
single photon emission CT
99mTc used - inject into pt
check for activity of joint
- good for condylar hyperplasia
- shows condylar activity in terms of metabolic turnover
- only used as screening method - doesn’t specify if due to overgrowth/neoplasia/inflammation
imaging for oncology
cross-sectional imaging with contrast
- CT
- MRI
- look for lymphadenopathy and size of primary tumour
- also do chest and thorax to check for distant metastasis
US guided biopsy of cervical lymphadenopathy
- if cervical node prominent
- core biopsy
PET/CT
DPT for dental assessment prior to radio
CT vs MRI
MRI no radiation dose to pt MRI takes longer more contraindications for MRI - pacemakers, claustrophobic, cochlear implants MRI better for assessing: - perineurial spread - bone invasion via bone marrow changes - ST characteristics of lesion
PET
Positron Emission Tomography
nuclear medicine technique
radioactive fluorine labelled glucose injected (18-FDG)
goes to metabolically active tissues
can’t talk after injected as glucose will go to vocal cords (false positive of laryngeal tumour)
doesn’t give anatomical detail so overlaid onto CT/MRI (to locate hotspot)
good for looking for unknown primary tumours
useful for follow-ups and recurrence
FOM and oropharynx avid result likely due to tongue movement
