oncology and bony imaging

Question 1

what is used for bony imaging?

Answer 1

CBCT/CT
- superior for visualising cortical bone changes
MRI to check for changes in marrow pattern
- inflammation/neoplasia

Question 2

CBCT

Answer 2

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

Question 3

CBCT smaller voxel =

Answer 3

higher resolution

Question 4

CBCT isotropic

Answer 4

equal measurements in all directions - height, width, depth

cubes of data with equal measurements

Question 5

how is CBCT taken?

Answer 5

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

Question 6

interpreting CBCT

Answer 6

cortical bone white
air black
ST grey - difficult to distinguish from SC fat

Question 7

comparing CT and CBCT - beam

Answer 7

CBCT cone shaped

CT fan shaped

Question 8

comparing CT and CBCT - dose

Answer 8

CBCT low

CT high

Question 9

comparing CT and CBCT - contrast

Answer 9

CBCT none

CT use of iodinated for ST

Question 10

comparing CT and CBCT - positioning

Answer 10

CBCT - upright seated/standing

CT - horizontal

Question 11

uses of CBCT

Answer 11

ORN/MRONJ
 - moth eaten appearance 
 - precisely locate sequestra
osteomyelitis
 - moth eaten appearance
further investigation of odontogenic lesions
 - cysts and tumours

Question 12

TMJ imaging - myofascial (parafct habits)

Answer 12

no imaging required

give conservative advice

Question 13

TMJ imaging - internal derangement

Answer 13

MRI gold standard
- can visualise disc
- parasagittal and paracoronal planes
US alternative e.g. if pt is claustrophobic, articular disc not visualised in US

Question 14

TMJ imaging - degenerative - osteoarthritis/RA

Answer 14

CBCT / (CT)
loss of uniformly thick cortical bone
osteophyte - projection of new bone
thinning and erosion

Question 15

facial asymmetry

Answer 15

condylar head different trabecular pattern in part could suggest neoplastic change

Question 16

how does MRI work?

Answer 16

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

Question 17

T1W MRI

Answer 17

good for anatomy
fat white
cortical bone black
fluid and air black

Question 18

T21 MRI

Answer 18

fat and fluid white

Question 19

TMJ imaging - radionucleotide SPECT

Answer 19

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

Question 20

imaging for oncology

Answer 20

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

Question 21

CT vs MRI

Answer 21

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

Question 22

PET

Answer 22

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