Alternative Imaging Modalities Flashcards
plain radiographs?
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
what is a CT?
uses xray photons
patient in a scanner
xray tube and detector rotate around pt
in a CT patient divided into?
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
colours of tissues on a CT?
bone = white st = grey air = black
in a CT an image can be manipluated to allow?
better visuals of more subtle changes between tissues = windowing
advantages of CT?
bone and soft tissue seen = differentiates different tissues e.g in a head injury can see brain and bone
speed
multiplanar
cost/availability
disadvantages of CT?
dose to head about 2msV
often requires intavenous contrast to distinguish tissues - iodine
artefacts - from metallic objects e.g amalgam
expensive
uses of CT?
generally head and neck
intracranial bleeds, trauma, evaluate bony lesions, salivary glands, neoplasia, implant planning, orthogenic assesment and treatment planning
how are CT scanners characterised?
by field of view
what is a voxel?
volume element pixel with depth size varies : 0.08mm - 0.4mm smaller voxels = higher resolution image smaller = longer scan time and dose
advantages of a CBCT?
3D
multiplanar
dose of CT
disadvantages of a CBCT?
artefact from high attenutation objects
scan time of periapicals
dose of radiographs
data is reconstructed into what planes?
axial
coronal
saggital
other - dental arches, specific cross sections
what is a CBCT used for?
implantology localisation of impacted teeth and effect on adjacent structures endo pathology trauma
what is an MRI?
protons - water
a magnetic field
radiofrequency of pulses
good for soft tissues
on an MRI what is always black?
cortical bone/dental hard tissues
with an MRI, different frequencies make the tissues diff colours e.g?
T1 - water is dark
T2 - water is bright
T1 gen anatomy, T2 gen pathology
advantages of an MRI?
no ionising radiation
excellent soft tissue view
also bone - changes in marrow - infection/infiltration or cortex breach
multiplanar
disadvantages of an MRI?
contraindications - pacemarker, heart valves, intracerebral aneurysm clips, 1st trimester of pregnancy danger with the strong magnetic field availability/expensive scan times claustraphobia
MRI’s used for?
head/neck - intracranial pathology salivary gland disease soft tissue disease bone disease TMJ disc/bone implant planning
what is an ultrasound?
high frequency sound waves over 13MHz
transducer placed on skin
advantages of ultrasound?
no radiation no harmful effetcs ideal for superficial soft tissue structures multiplanar realtime images blood flow used to guide fine needle to aspirate
disadvantages of ultrasound?
operator dependent
hard to interpret
superficial tissues only cant penetrate bone
what are ultrasounds used for?
neck swelling
salivary glands
blood flow
guidance for biopsy/drainage
what is radioisotope scanning?
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
what is technetium?
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
what is radioisotope scanning used for?
salivary gland function
condlye growth in mandibular symmetry
thryoid - bone metastases
osteomyelitis
disadvantages of radioisotope scanning?
poor resolution
appearances not specific and may not be distinguishable between different pathological processes
radiation dose
