Imaging Flashcards
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
Define contrast media
these are solutions of non toxic substances that contain elements of high atomic number
what do you do in order to increase the average atomic number of a hollow structure
- you fill the cavities with a liquid with a much higher average atomic number
describe the difference in densities in contrast media
- large difference in densities of two organs show up such as the solid muscle in the heart and the airs in the lungs
- if two organs have similar densities then they do not show up such as the small intestine and large intestine
how do you reduce the density of a hollow organ
- fill it with gas or air
how do you give barium
Barium is non toxic – give it in differnte ways
Swallow – looks at the oseophogus and goes down to the stomach after time and the small insteine
Rectum – becomes an enema – jiggles the person around as your working against the normal flow, takes 30 minutes to jiggle the person around to get to the colon
Will be excreted and go back out
Few people that asparate it – goes into the lungs instead of the osphogus
how do you give iodine
- non toxic
- inject it into the vascular system either in the arteries or the veins
describe the radiation in CT
Normal background radiation per year is around 3.0 mSv, coast to coast flight across US adds 0.03 mSv
CT of abdo and pelvis = 10 mSv versus radiograph 8 mSv
Radiograph of arms or legs 1.5 mSv bone DEXA 0.001 mSV
Chest x-ray 0.1 whereas mSV chest CT 7 mSv, therefore it is higher, as your taking multiple x ray images down the chest
when looking at axial scans how do you look at them
- look at them as if your standing from the head of the individual
MRI what is T1 and what is T2
T1 – fat white
T2 – high free water white (oedema) – sees pathological process and measures water
what does gadolinium do
goes across the blood brain barrier
- contrast enhancemnet
