Alternative Imaging Modalities

Question 1

plain radiographs?

Answer 1

2D superimposition
multiple views for localisation
limited use for soft tissues
ionising radiation
static picture requiring demineralisation
sensitivity/specificity
but = cheap,readily available, relatively low dose

Question 2

what is a CT?

Answer 2

uses xray photons
patient in a scanner
xray tube and detector rotate around pt

Question 3

in a CT patient divided into?

Answer 3

voxels = pixels with volume
each voxel is given a CT number according to amount it has attenuated the beam
different CT number = different shades of grey

Question 4

colours of tissues on a CT?

Answer 4

bone = white
st = grey
air = black

Question 5

in a CT an image can be manipluated to allow?

Answer 5

better visuals of more subtle changes between tissues = windowing

Question 6

advantages of CT?

Answer 6

bone and soft tissue seen = differentiates different tissues e.g in a head injury can see brain and bone
speed
multiplanar
cost/availability

Question 7

disadvantages of CT?

Answer 7

dose to head about 2msV
often requires intavenous contrast to distinguish tissues - iodine
artefacts - from metallic objects e.g amalgam
expensive

Question 8

uses of CT?

Answer 8

generally head and neck
intracranial bleeds, trauma, evaluate bony lesions, salivary glands, neoplasia, implant planning, orthogenic assesment and treatment planning

Question 9

how are CT scanners characterised?

Answer 9

by field of view

Question 10

what is a voxel?

Answer 10

volume element
pixel with depth
size varies : 0.08mm - 0.4mm
smaller voxels = higher resolution image
smaller = longer scan time and dose

Question 11

advantages of a CBCT?

Answer 11

3D
multiplanar
dose of CT

Question 12

disadvantages of a CBCT?

Answer 12

artefact from high attenutation objects
scan time of periapicals
dose of radiographs

Question 13

data is reconstructed into what planes?

Answer 13

axial
coronal
saggital
other - dental arches, specific cross sections

Question 14

what is a CBCT used for?

Answer 14

implantology
localisation of impacted teeth and effect on adjacent structures
endo
pathology
trauma

Question 15

what is an MRI?

Answer 15

protons - water
a magnetic field
radiofrequency of pulses

good for soft tissues

Question 16

on an MRI what is always black?

Answer 16

cortical bone/dental hard tissues

Question 17

with an MRI, different frequencies make the tissues diff colours e.g?

Answer 17

T1 - water is dark
T2 - water is bright
T1 gen anatomy, T2 gen pathology

Question 18

advantages of an MRI?

Answer 18

no ionising radiation
excellent soft tissue view
also bone - changes in marrow - infection/infiltration or cortex breach
multiplanar

Question 19

disadvantages of an MRI?

Answer 19

contraindications - pacemarker, heart valves, intracerebral aneurysm clips, 1st trimester of pregnancy
danger with the strong magnetic field
availability/expensive
scan times
claustraphobia

Question 20

MRI’s used for?

Answer 20

head/neck - intracranial pathology
salivary gland disease
soft tissue disease
bone disease
TMJ disc/bone
implant planning

Question 21

what is an ultrasound?

Answer 21

high frequency sound waves over 13MHz

transducer placed on skin

Question 22

advantages of ultrasound?

Answer 22

no radiation
no harmful effetcs
ideal for superficial soft tissue structures
multiplanar
realtime images
blood flow
used to guide fine needle to aspirate

Question 23

disadvantages of ultrasound?

Answer 23

operator dependent
hard to interpret
superficial tissues only cant penetrate bone

Question 24

what are ultrasounds used for?

Answer 24

neck swelling
salivary glands
blood flow
guidance for biopsy/drainage

Question 25

what is radioisotope scanning?

Answer 25

inject unstable isotopes and decay emitting radioactive particles -a.b or radiation = g
isotope selected according to tissue to be imaged
radioactive compound concentrated in target tissue indicating = increased activity - hotspot, decreased activity - cold spot
radioactive emissions detected by gamma camera

Question 26

what is technetium?

Answer 26

99mTc
short half life of 6hours = lower patient dose
easily available
binds easily to different substances e.g mdp in bone, red blood cells
taken up by thyroid and salivary glands

Question 27

what is radioisotope scanning used for?

Answer 27

salivary gland function
condlye growth in mandibular symmetry
thryoid - bone metastases
osteomyelitis

Question 28

disadvantages of radioisotope scanning?

Answer 28

poor resolution
appearances not specific and may not be distinguishable between different pathological processes
radiation dose