MEDICAL IMAGING Flashcards
what is X ray production
electrons are emitted from a hot filament and then accelerated with a high voltage, which increases the kinetic energy.
the electrons are then fired at the anode
what is the X ray curve
obtained when energetic electrons strike a material
the smooth part of the spectrum is called bremsstahlung radiation
the peaks are characteristics of the anode material
is cathode positive or negative?
negative
how is an X ray formed
de accelerating an electron
why does qv=hf
e=hf
e=qv
Why does the intensity over wavelength graph plateau as the wavelength increases and the intensity decreases
energy is converted into heat
what is the compton effect
high energy x ray photon, bounces off electron, the x ray photon changes direction and loses energy to the electron. Lower energy x ray. The bigger the angle the electron the bigger the loss of the energy
what is the attenuation coefficient
the amount of xray absorbed per meter, if you double the thickness of the material, it will quarter the the radiation
what experiments did wilhelm Rontgen carry out
passing current through an evacuated glass tube, with a high voltage cathode and anode. He noticed that it could travel through glass and the dark paper around it, annd cause a fluorescent plate near his apparatus to grow.
what are the nature of X rays
have both wave and particle like properties. They can be diffracted, which display a pattern that correspond with the wavelengths between 10^-12 ans -9.
they can also behave like a stream of particles called photons.
how can x rays be produced in a glass chamber
thermionic emission from cathode, electrons are emitted, and accelerated (kvp) then decelerated by colliding with anode
what is thermionic emission
release of electrons or ions in response to heat
how does increasing kVp effect, electron and x ray energy
proportionally
how does increasing mA EFFECT ELECTRONS AND XRAYS
Proportionally, more electrons
why is the glass tube evacuated.
the electrons would lose energy colliding with any glass molecules in their path.
is the maximum energy of a xray limited by the energy the electron gained while being accelerated through a voltage? reference an equation
yes= eV
e=hf=eV
fmax=ev/h
λmin=hc/eV
since maximum frequency occurs for minimum wavelength.
what does attenuation mean
a gradual decrease in intensity
what is the attenuation coefficient
is a constant used to calculate how the intensity of X-rays decreases as they pass through a material. Units are : m^-1
what are the four ways X-rays can interact with materials
simple scattering
the photoelectric effect
pair production
compton effect
in photoelectric effect, all the incident x ray energy is -“”
absorbed
what is simple scattering
when low energy X rays encounter electrons in an atom, the energy of the X ray photon is not sufficient to cause ionisation. The photon is instead scattered (direction changed), there is no overall change in energy, It causes noise in the image.
what is the photoelectric effect (for Xrays)
Xrays are capable of releasing free electrons from atoms. Apply the conservation of energy to the photoelectric effect.
Energy of incoming photon=work function + maximum Ek of photon
explain the compton scattering experiment
Compton used monochromatic X-rays , obtaining these by filtering out the wavelengths except those which correspond with the highest peaks of intensity. Compton used an Xray spectrometer to measure the wavelengths of the scattered radiation from a carbon target. he deduced that some wavelengths were longer than the initial WLs. The orbital electron is emitted with a fraction of the kinetic energy, and the rest is emitted as a photon. Mass-energy is conserved. The Xray photon and electron are scattered in diff directions due to the conservation of momentum. Any photon deflected through a large angle would would have lost more energy.
what is pair production
in a beam of high frequency X-rays, it is possible for a photon of Xrays to interact with the nucleus of an atom and ofr the xray photon to vanish ,spontaneously producing a positron and electron pair.
pair production
energy of an X-ray photon→?
0 0
e + e
1 -1
how can we find the minimum energy required for pair production?
e=mc^2
explain X-ray absorption by the patient
the amount of absorption by both tissue and bone varies considerably with the frequency of the x ray.
low energy x rays are absorbed mostly by photoelectric effect. at higher frequencies, compton scattering is more frequent. at very high, pair production is much more common.
how can attenuation coefficients vary
with the energy of the X rays.
whats is CAT.
Computerised axial tomography.Is a process using multiple scans to produce images of slices, in order to create a 3d image.
advantages of a cat scan over an X ray image
provides the doctor with accurate visuals
sensitive to changes in density, and give much better contrast to soft tissues. can see the tissues through multiple angles
what is a tracer?
a radioactive substance either ingested or injected into a patient, it emits gamma photons to be detected by a gamma camera
what is a gamma camera?
detects gamma photons emitted from a patient. This is used to produce a real time image of the parth of the tracer through the body
what is a collimator
is a device for producing a parallel sided beam of electromagnetic radiation.
what is a scintillator
material which produces photons of visible light when struck by a high energy photon.
what is a photomultiplier tube
is a device used to give a pulse of electrons for each incident photon.
what are the uses of radioactive medical tracers
must be put into a patients body to diagnose or treat an illness.
why must radioactive medical tracers use gamma
alpha and beta would be absorbed by the tissues, and remain undetected.and would also damage the body because of the ionising power.
what is positron emission tomography
is the use of photons produced when positrons annihilate with electrons.
what is ultrasound
waves are longitudinal above the u[pper limit of the audible range.§
what is a transducer
is a device which converts a non electrical signal into an electrical signal.
piezoelectric effect
is the change in volume of a material when a p.d is applied across its opposite faces. alternatively, it is the production of an induced e.m.f. when crystals are put under stress.
