25 Flashcards
what kind of radiation is in an X-ray
heterogenous ionising radioation, gamma radiation at diff wavelengths.
in an xray, what densities are black? white? grey?
Air = black Fat = light grey Soft tissue/fluid = shades of grey Calcium = most dense naturally occurring tissue Metal = white
what is the main use of x rays
skeletal system and some diseases in soft tissue
advantage of x rays
Quick
Cheap
Most common readily available –> First call you request
disadvantages of x rays
2D representation of a 3D object
things in front can hide things that are behind and you cant see into the bone itself.
Don’t get good view of muscle tissue and other soft tissues bc of density pb
Limited range of densities that can be seen in x ray
Only calcified tissue shows up clearly
Soft tissues do not show up very well
Not very sensitive
You have to loose 30% of bone mass before it shows up on an X-ray
Processes taking place inside the bone can not be seen (avascular necrosis, osteomyelitis etc)
You sometimes have to do lateral view to see other structures
what view are CHEST x rays taken in
PA view.
why is the dome of the diaphragm higher on the right side
bc liver is dense organ so pushes diaphragm further up, even when stomach fills w food its not that dense
what view is most commonly used for the APPENDICULAR SKELETON
AP and lateral view, bc doesn’t matter if things are distorted
what color is radioopaque
white (v dense)
what coloraturas is radio Lucent
black (less dense)
what’s situs inverses totals
all the organs are the other way around, BUT be careful maybe it hasn’t been labelled properly
what’s dextrocardia
when only the heart is flipped
what are epiphyseal growth plates
Bones need to grow so plate of cartilage at either ends of bone which become bones after to allow bones to lengthen
what’s a pneumothorax
(air in intrapleural space between parietal and visceral pleura causing right lung to collapse)
what’s a DEXA scan
Two different low energy X-ray sources (heterogenous)
The denser the bone the fewer X-rays that get to the detector
Using 2 different X-ray rather than massive amount of sources improves accuracy
Used to detect ostoeporosis and body fat compositin
Lower levels of xray comparired to normal radiograph
X ray of arm of legs give you 1.5milisivers vs dexoscan 0.001 milisivers so much lower x ray exposure
why would you use a contrast medium
Large difference in the densities of two organs show up
e.g solid muscle of the heart and the air in the lungs
If two organs have similar densities then do not show up
e.g. the small and large intestines
Reduce the density of a hollow organ by filling it with gas or air, provides negative contrast
Increase average atomic number of hollow structure (ie making it denser) by filling cavity with a liquid with a much higher average atomic number
Contrast media are solutions or suspensions of non-toxic substances that contain elements of high atomic number
Barium
Iodine
Gadolinium
No longer used bc it caused discomfort and air that had to be expelled so not pleasant
what 3 contrast mediums exist and what are they used for
barium sulfate for GI
iodine for vascular system
gavalinium used for MRI
what’s a CT scan
Here multiple x ray beans at diff angles passing through body to diff detectors, builds up picture of inside of body w more accuracy
CT scan advantage
Cross-sectional images and other planes can be reconstructed afterwards or 3D reconstructions
Good high contrast bone detail so good for calcified tuissue
Well tolerated (not claustrophobic noisy)
Readily available
CT scan disadvantage
Ionising radiation dose is higher bc multiple x ray sources so NOT FOR PREGGOS
Metallic artefacts cause loss of detail
Soft tissue surrounded closely by bone difficult to image
Respiratory movement artefact cause loss of details that’s why they tell you not to breath and hold your breath
Sturcutures that are close to ech other can lead to loss of details
Whats an MRI
uses magnets instead of ionising radiation
MRI advantage
Very high soft tissue contrast bc soft tissue has lots of water which has hydrogen ions
Images acquired in transverse plane (patient passes through the MRI lying down)
Can be reconstructed in any plane
Can get both structural and functional information
disadvantage
Does not image bone directly (bones only 5% water)
what’s an ultrasound
non ionising radiation based on density how d¡sound waves are absorbed by tissue and bounce back to receiver.
advantages of ultrasound
Safe during fetal development as no radiation
Cheap
Readily available
Becoming more common for both diagnosis and therapeutic imaging
But difficult to interpret what is going on
Gives you real time imaging
Not as clautrophobic and noisy as MRI
what’s the difference between T1 and T2 wighted MRI imaging o
The timing of radiofrequency pulse sequences used to make T1 images results in images which highlight fat tissue within the body.
The timing of radiofrequency pulse sequences used to make T2 images results in images which highlight fat AND water within the body.
