Principles of Radiography Flashcards
What are xrays?
EM radiation - non particulate radiation that travels in a straight line through a vacuum
What colour are bones in a positive image
Dark
Bones are white in a negative image
How are xrays produced and what is required for this process?
Fast electrons collide with atoms of a heavy metal eg. tungsten
- source of elecctrons
- accelerator
- heavy metal target
Why is copper used to support the tungsten target@
Heat sink
What is the purpose of a collimator?
Shapes the electron beam to the area required.
What 3 factors affect absorption of xrays in the body?
Density
Thickness
Atomic number of material
[as these ^ no. electrons in the path of the xray beam to interfere with it]
Why is an aluminium filter used on the xray beam?
Filters out low energy radiation which would otherwise sunburn patient
Allows high energy radiation to pass through still
What 5 types of tissue may be distinguished on radiographs?
Air (lungs, intestine) LUCENT
Fat
Soft tissue (parenchymal organs, body fluids, muscle)
Calcified tissues and bones
Metal/^ Atomic No. materials (L/R marker, contrast mediums) OPAQUE
What do mAs refer to?
mA: Current (No. Electrons) passing across the xray tube
s: Duration of current
^current or time -> ^ total number of electrons, ^ no. xrays, IMAGE WILL BE DARKER
Xrays will have the same average energy but there will be more of them
What is the typical range of mAs used to radiograph small animals? Why would you adjust the mA and s settings?
25-300 mA
0.01 - 0.3s
Upper end of these ranges will make the radiograph DARKER
Increasing mA allows time to be decreased and prevents motion blur
What is the kVp
kilovoltage peak - maximum voltage applied across the xray tube. Increased the kVp increases BOTH the no. xrays produced AND their average energy
- increases the penetrating power of the beam
When and how is the kVp adjusted?
Low kVp used for thin/small body parts
High kVp used for thicker eg. thorax - penetrates deeper
Where is the contrast medium injected for an angiogram?
Carotids to enter vie the brachiocephalic trunk
What 3 types of contrast medium exist?
Positive - eg. Iodide solution for bladder, IV Barium Sulphate meal GIT Negative - eg. Gases Double - eg. Distend using gas Add positive medium
What is Bremsstrahlung radiation principle?
Electrons fired at the heavy metal target interact with the nucleus and electrons, changing the direction. The velocity is lowered, KE drops and direction changes. Remaining energy is given off as an xray.
