Intro to radiography Flashcards
Clinical context of radiography
state of patient
relevant previous history
other investigations
Diagnostic context of radiography
differential diagnosis?
what questions are we trying to answer?
why is there doubt?- another test if 1st test is normal
x rays densities
black- air
dark grey- fat
light grey- soft tissue
white- bone/ metal
pros of radiography
quick, cheap, easy, universal, well understood
cons of radiography
2D, artefact, radiation
abnormality during x ray
loss of silhouette sign - cannot see border
common uses of radiography
fracture, failure vs pneumonia, bowel obstruction
CT
x ray source exposure at different angles generating 2D- multiply to make 3D same 4 densities IV and oral contrast toxic, can damage kidneys
modern CT
volume of data for reconstruction, fast- can track contrast and recreate image with structure with most contrast (isolate)
Stroke
urgent CT to decide on thrombolysis- clot busting drug if haemorrhage (white on CT) no thrombolysis because can bleed to death
CT windowing
4000 shades of grey but eye can only see 50 so you can window to select part to display
CT common uses
trauma, cancer staging, abdominal sepsis
CT pros
quick, good spatial detail, reconstructions
CT cons
poor tissue contrast (better with contrast media)
high radiation dose (often needed repeated exams)
Fluoroscopy
continuous screening of patients with x ray with some contrast
inject or drink barium
dynamic assessment
fluoroscopy common uses
upper GI, angiography, renal tract imaging
fluoroscopy pros
adaptable
structure and function
fluoroscopy cons
high radiation dose (repeats)
invasive
planar imaging
Ultrasound
piezoelectric crystals to produce US wave
work out depth of structure
electric signals to sound then reflects back- electric current
US common uses
abdominal pain
renal tract imaging
musculoskeletal
US doppler effect
to measure blood flow
find tumours as lots of blood flow is there, when sound comes towards you the waves compress
US pros
very safe
cheap
portable
good for superficial vessels
US cons
variable
artefact
limited info
MRI
magnet to align protons
radiowaves sent to excite them, let them relax (relaxes at different rates)
collect emitted energy
other applications of MRI
time delays to see how mobile protons are- diffusion weighted
find direction and map- diffusion tensor
analyse chemical signature
MRI common uses
brain and spine imaging
MSK
tumour characterisation
MRI pros
structure and function
no ionising radiation
MRI cons
time consuming
claustrophobia
artefact
magnets
Nuclear medicine
not good for structure
can repeat image
large areas/ specific organs
Nuclear medicine and CT
PET-CT- extra dose
SPECT- volume imaging like normal CT but with isotope
Nuclear and CT common uses
TUMOURS bone imaging lungs renal function thyroid
nuclear and CT pros
structure and function
relatively specific- narrow Dx
nuclear and ct cons
ionising radiation
time consuming
poor spatial resolution
interventional radiology
new field- using imaging to guide therapy- often angiography and US
image guided surgery
neuronavigation
virtual training
risks of radiography
radiation contrast media nephrotoxic invasive procedures artefact- misdiagnosis, false reassurance, further tests incidental findings
what can we do
sensible referrals
optimise techniques
ALARA as low as reasonably achievable
conscientious vetting- ‘scan if you must’
radiology and law
ionising radiation (medical exposure regulations) 2000 concerned with patient dose and radiology staff
referrer required to provide sufficient clinical info in order that the practitioner can make a decision about justifying the medical exposure
