MEDICAL IMAGING

Question 1

what is X ray production

Answer 1

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

Question 2

what is the X ray curve

Answer 2

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

Question 3

is cathode positive or negative?

Answer 3

negative

Question 4

how is an X ray formed

Answer 4

de accelerating an electron

Question 5

why does qv=hf

Answer 5

e=hf
e=qv

Question 6

Why does the intensity over wavelength graph plateau as the wavelength increases and the intensity decreases

Answer 6

energy is converted into heat

Question 7

what is the compton effect

Answer 7

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

Question 8

what is the attenuation coefficient

Answer 8

the amount of xray absorbed per meter, if you double the thickness of the material, it will quarter the the radiation

Question 9

what experiments did wilhelm Rontgen carry out

Answer 9

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.

Question 10

what are the nature of X rays

Answer 10

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.

Question 11

how can x rays be produced in a glass chamber

Answer 11

thermionic emission from cathode, electrons are emitted, and accelerated (kvp) then decelerated by colliding with anode

Question 12

what is thermionic emission

Answer 12

release of electrons or ions in response to heat

Question 13

how does increasing kVp effect, electron and x ray energy

Answer 13

proportionally

Question 14

how does increasing mA EFFECT ELECTRONS AND XRAYS

Answer 14

Proportionally, more electrons

Question 15

why is the glass tube evacuated.

Answer 15

the electrons would lose energy colliding with any glass molecules in their path.

Question 16

is the maximum energy of a xray limited by the energy the electron gained while being accelerated through a voltage? reference an equation

Answer 16

yes= eV
e=hf=eV
fmax=ev/h
λmin=hc/eV

since maximum frequency occurs for minimum wavelength.

Question 17

what does attenuation mean

Answer 17

a gradual decrease in intensity

Question 18

what is the attenuation coefficient

Answer 18

is a constant used to calculate how the intensity of X-rays decreases as they pass through a material. Units are : m^-1

Question 19

what are the four ways X-rays can interact with materials

Answer 19

simple scattering
the photoelectric effect
pair production
compton effect

Question 20

in photoelectric effect, all the incident x ray energy is -“”

Answer 20

absorbed

Question 21

what is simple scattering

Answer 21

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.

Question 22

what is the photoelectric effect (for Xrays)

Answer 22

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

Question 23

explain the compton scattering experiment

Answer 23

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.

Question 24

what is pair production

Answer 24

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.

Question 25

pair production
energy of an X-ray photon→?

Answer 25

0 0
e + e
1 -1

Question 26

how can we find the minimum energy required for pair production?

Answer 26

e=mc^2

Question 27

explain X-ray absorption by the patient

Answer 27

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.

Question 28

how can attenuation coefficients vary

Answer 28

with the energy of the X rays.

Question 29

whats is CAT.

Answer 29

Computerised axial tomography.Is a process using multiple scans to produce images of slices, in order to create a 3d image.

Question 30

advantages of a cat scan over an X ray image

Answer 30

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

Question 31

what is a tracer?

Answer 31

a radioactive substance either ingested or injected into a patient, it emits gamma photons to be detected by a gamma camera

Question 32

what is a gamma camera?

Answer 32

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

Question 33

what is a collimator

Answer 33

is a device for producing a parallel sided beam of electromagnetic radiation.

Question 34

what is a scintillator

Answer 34

material which produces photons of visible light when struck by a high energy photon.

Question 35

what is a photomultiplier tube

Answer 35

is a device used to give a pulse of electrons for each incident photon.

Question 36

what are the uses of radioactive medical tracers

Answer 36

must be put into a patients body to diagnose or treat an illness.

Question 37

why must radioactive medical tracers use gamma

Answer 37

alpha and beta would be absorbed by the tissues, and remain undetected.and would also damage the body because of the ionising power.

Question 38

what is positron emission tomography

Answer 38

is the use of photons produced when positrons annihilate with electrons.

Question 39

what is ultrasound

Answer 39

waves are longitudinal above the u[pper limit of the audible range.§

Question 40

what is a transducer

Answer 40

is a device which converts a non electrical signal into an electrical signal.

Question 41

piezoelectric effect

Answer 41

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.