Imaging Flashcards
(34 cards)
what does X ray use
uses an heterogenous beam of x rays
describe how an X ray works
- Based on the density and composition of the structure some of the x rays will be absorbed
- The x rays that pass through are black and these are the less dense tissues
- Grey and white areas are areas that have absorbed more x rays and are therefore white
what are the advantages of plain radiograph
- Cheap
- Readily available
- Uses ionising radiation
not catastrophic - come portable if the patient can’t get to the suite and can take into the operating theatres
- can find some diseases in soft tissue but you need a contrast medium
what are the disadvantages of plain radiographs
- Only calcified tissue shows up clearly
- Soft tissues don’t show up very well
- Not sensitive – have to loose 30% of bone mass before it shows up on an x ray
- Things in front can obscure structures behind
- Processes taking place inside the bone cannot be seen
- 2D representation of a 3D object
what does radio-opaque mean
white - areas that block the x rays
what does radio-lucent mean
black - areas that did not stop the x rays
what does a dexa scan do
- Two different low energy X ray sources
- The denser the bone the fewer x rays that get to the detector
what does 2 different x ray sources do in the DEXA scan
- provides and improves higher accuracy
What is the DEXA scan used for
- Used for body mass calculations
- Used for diagnosis and following of bone density changes in osteoporosis
what does contrast media do
show differences
- barium and iodine issued with contrast
- gadolinium is used in MRI
what does CT do
- Uses multiple x ray beams at different angles to build up a cross section of the bodies organs and tissues
what are the advantages of CT
- Cross sectional images and other planes can be reconstructed afterwards or 3D reconstructiosn
- Good high contrast bone detail
- Well tolerated
- Radily available
what are the disadvantages of CT
- Ionising radiation dose
- Metallic artefacts cause loss of detail
- Soft tissue surrounded closely by bond difficult to image
- Respiratory movement artefact
how does MRI work
- Uses non-iosning radiation – 10,000-30,000 times the earths magnetic field
what are the advantages of MRI
- Very high soft tissue contrast
- Images acquired in transverse plane – can be reconstructed in any plane
- Can get both structural and functional information
- Safe during fetal development as no radiation
- Cheap
- Readily available
- common for both diagnosis and therapeutic imaging
what are the disadvantages of MRI
- does not image bone directly
- difficult to interpret whats going on
- noisy
- catastrophic
how does MRI work
- Based on sound waves with frequencies usually in rnage of 1-18megahertz
what does PA stand for
posterior to anterior
what do you always show in radiographs
always show the image from the front
describe the view in PA
- Clavicle in lung field
- Ribs slanted (posterior ribs distinct)
- Scapula outwards from lung field
- Heart shadow smaller
- Usual view for the chest as it does not show the heart being magnified
describe the view in AP
- Clavicle remains at top of lung field
- Ribs lie more horizontal (anterior ribs more distinct)
- Scapula comes in the lung field
- Heart shadow looks larger
- Usually bedridden and infants
for the appendicular skeleton…
AP and lateral views are most common
why are AP and Lateral views used in the appendicular skeleton
Need two view to be able to get view
Need AP to get a head on view and lateral view to see if you can see anything that you can see from the front
what is a difference in children X rays
different cartilage isn’t calcififed, if the cartailage plate is not calficided appears as a radiolucent line that appears in childrens x rays, this is where the bone is growing and is a growth plate, not a fractured
