Medical Imaging

Question 1

How is an X-Ray created?

Answer 1

Deceleration of electrons at the anode (target metal) converts their KE into high energy photons

Question 2

Basic structure of X-ray

Answer 2

Electrons accelerated from cathode due to high temperature (thermionic emission)
Vaccinated glass tube
Target metal attached to spinning motor to prevent overheating

Question 3

Max energy of x-ray photon

Answer 3

Voltage x charge

Question 4

Efficiency of X-ray

Answer 4

1% of energy converted to photons

Question 5

Attenuation of X-rays

Answer 5

I=I₀e^-μx

Question 6

what are I, I₀, μ, x

Answer 6

Intensity
Initial intensity
Attenuation coefficient
Distance from surface

Question 7

Describe simple scatter

Answer 7

Simple scattering occurs when an X-ray photon interacts with an atom and is scattered with no change in energy

Question 8

Describe Compton effect

Answer 8

Compton scattering occurs when an X-ray photon removes an electron from an atom and is scattered with reduced energy

Question 9

Describe pair production

Answer 9

Photon absorbed and creates electron-positron pair (1.1MeV)

Question 10

Describe photoelectric effect

Answer 10

Photon absorbed by an electron which its ejected from the atom. gap in electron is filled by another electron which emits a photon.

Question 11

what is attenuation coefficient proportional to

Answer 11

μ∝Z³

Question 12

properties of contrast media

Answer 12

high proton number
iodine/ barium

Question 13

Define thermionic emission

Answer 13

when electrons are released from a material by heating it

Question 14

what is a radiopharmaceutical

Answer 14

medical tracer; radioisotope (fluorine-18/ technetium-99m) combined with other elements to target specific organ

Question 15

features of technetium-99m

Answer 15

emits gamma radiation
half life of 6 hours
decays to stable isotope

Question 16

features of fluorine-18

Answer 16

used in PET scans
undergoes beta plus decay
half life of 110 minutes

Question 17

what is a collimator

Answer 17

hollow lead tubes which only let gamma rays pass if they are directly bellow them

Question 18

whats is a scintilator

Answer 18

above the collimator, prudes photons of visible light when gamma ray hits it

Question 19

what are photomultiplier tubes

Answer 19

photons incident at the photocathode produce cascade of electrons which produces pulse of voltage at the end of the tube

Question 20

how does transducer emit ultrasound

Answer 20

crystal supplied with alternating potential difference to expand/contract it which causes sound waves to be produced at high frequencies.

Question 21

how does reflection of ultrasound at boundary depend on the physical property of the material

Answer 21

there will be no reflections if both materials have the same impedance.
Large difference in impedance will provide with most reflection
fraction of reflected intensity= (z2-z1)^2 / (z2+z1)^2

Question 22

how are ultrasounds used to measure blood flow

Answer 22

ultrasound waves reflected at angle to the blood flow
work out speed from change in frequency of the reflected wave caused by doppler shift