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principles of diagnostic imaging questions and answers graded A+

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  • Course
  • Radiology imaging
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  • Radiology Imaging

principles of diagnostic imaging questions and answers graded A+

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  • August 8, 2024
  • 27
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers
  • Radiology imaging
  • Radiology imaging
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BravelRadon
principles of diagnostic imaging

why is electromagnetic radiation best for image formation? - correct answer ✔✔travels in straight lines



velocity of EM radiation? - correct answer ✔✔speed of light (this stays constant)



energy of EM radiation? - correct answer ✔✔inversely proportional to wavelength

(shorter wavelength = higher energy)



how are x-rays different from gamma rays? - correct answer ✔✔different based on how they're formed:

>Xrays: produced by interaction of fast moving electrons with metal (tungsten) target and used in
radiography

>gamma rays: produced by decay of radioactive elements and used in nuclear medicine (scintigraphy)



what does heating the cathode of a x-ray machine do? - correct answer ✔✔'thermionic emission' =
cloud of electrons around cathode



how is a xray produced? - correct answer ✔✔>tungsten wire filament heated by small electric current =
cloud of free electrons around cathode

>electrons are focused in beam by a negatively charged focusing cup around the cathode

>electrons then accelerated towards anode by application of high PD between anode and cathode

>electrons rapidly decelerated upon interaction with anode atoms = x ray production



why is tungsten used in the cathode? - correct answer ✔✔used due to high atomic number (74) and
melting point (3380'C)



what is mA? - correct answer ✔✔AMOUNT OF XRAY

>alters the small current heating the cathode filament

,>the higher the filament current (mA), the higher the temperature heating the cathode = greater
number of electrons produced = more xray



what is the normal potential difference applied to accelerate electrons towards the anode? - correct
answer ✔✔50-100,000V



what is kV? - correct answer ✔✔STRENGTH/PENETRATING POWER OF XRAY: alters the PD across the
tube, between the anode and cathode

(max energy of x-ray = kV across tube)



what is the focal spot (FS)? - correct answer ✔✔electrons from cathode are focused so they impinge on
small area (FS) of the anode



what is the general emission method of x-ray formation? - correct answer ✔✔>aka 'braking radiation'

>interaction of electrons = x-ray production



what is the characteristic emission method of x-ray formation? - correct answer ✔✔>electron knocked
out of target atom

>another falls down through shells to replace it → loss of energy = X-ray photon



why is x-ray production inefficient? what can be done to prevent this? - correct answer ✔✔Interaction
between electrons and anode = 99% heat and 1% x-rays so have to try and remove heat produced from
focal spot



what are the 2 methods of removing heat from the focal spot? - correct answer ✔✔1. stationary anode
(lower output machine)

>tungsten target embedded in block of copper = conduction of heat away from anode target

2. rotating anode (higher output machines)

>anode = disc (molybdenum or graphite- doesn't have to be conducting) with angled edge

>tungsten track runs round angled edge

>disc is mounted on a molybdenum rod rotated by electric motors (motors outside of the tracks)

>heat lost by convection from surface of disc as molybdenum is a poor conductor

, >have to 'prep' the x-ray machine as this starts the anode spinning and heats the cathode



what is the x-ray tube made of? - correct answer ✔✔evacuated pyrex tube containing anode and
cathode

>immersed in oil- helps heat conduction and electrical insulation

>entire tube surrounded by lead, except for a small window where useful X-ray beams emerge



how are the exposure factors of an x-ray altered? - correct answer ✔✔control panel on X-ray machine



what are the 4 exposure factors of an x-ray? - correct answer ✔✔>on/off button

>mA control

>kV control

>timer



why is the on/off button an xray exposure factor? - correct answer ✔✔>when X-ray machine is
connected to power supply, area around = 'controlled area' with access restrictions by law



what does the step up transformer do in the xray machine? - correct answer ✔✔increases voltage from
mains to supply the kV across the tube



what happens in the xray producing mechanism when you increase the kV? - correct answer ✔✔=
greater potential difference across X-ray tube = faster electrons between cathode and anode = more
kinetic energy when they hit anode = higher energy in resultant X-rays



when would you increase the kV and/or mA? - correct answer ✔✔thicker bodies



why is kV not linear? - correct answer ✔✔increase of 10kV = double energy



what happens in the xray producing mechanism when you increase the mA? - correct answer ✔✔=
hotter cathode filament = more electrons available to accelerate across tube = more electrons hit anode
= more X-rays produced (energy of xray = unchanged)

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