Exam (elaborations)
principles of diagnostic imaging questions and answers graded A+
- Course
- Institution
principles of diagnostic imaging questions and answers graded A+
[Show more]
Content preview
principles of diagnostic imagingwhy 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)
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller BravelRadon. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $20.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
72042 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now
