radionuclide

Question 1

what is beta decay?

Answer 1

neutron decays to porton + electron

Question 2

how are positrons emitted?

Answer 2

proton decays to neutron and positron

Question 3

what is the decay equation?

Answer 3

N=N0exp(-lamdat)
Lambda = decay constant
N = number of nuclei after time t

Question 4

why are gamma particles regularly used for nuclear medicine?

Answer 4

they have the energy to escape human tissue although they interact with matter (photoelectric and compton scattering)

Question 5

why are alpha particle less preferable for nuclear medicine?

Answer 5

their coulomb interaction causes short range travel - imaging not possible

Question 6

what are beta particles less preferable for nuclear medicine?

Answer 6

do not travel straight, undergo coulomb interaction, imaging impossible as their travel distance 1mm

Question 7

what is the purpose of a cyclotron?

Answer 7

produces PET radionuclides by smashing protons together with high energy, in a circular path by B field and vacuum chamber

Question 8

what are the two types of cyclotrons

Answer 8

1 ) shielded room (expensive but easy access for maintenance)
2) self shielded (compact, cheap, work near by but access difficult)

Question 9

how do nuclear reactors produce radionuclides?

Answer 9

by fission: uncle of heavy elements absorb thermal neutron, fission products = neutrons and radionuclide

Question 10

radionuclide generators produce what sort of radionuclides?

Answer 10

• short lived radionuclides

- ‘carrier free product’ daughter nuclides distinctly different to parents for seperation

Question 11

describe an ideal generator

Answer 11

• simple
• daughter yield high
• compact with shielding
• daughter stable, parent free
• sterile

Question 12

what is the decay equation for 99Tc?

Answer 12

99Mo -> 99mTc -> 99Tc

beta decay, than gamma decay 6 hours

Question 13

properties of photon emitting radio tracers for SPECT scan

Answer 13

• low energy gamma photons
• heavy nuclides label larger molecules
• majority use 99mTc

Question 14

how are tracer synthesised?

Answer 14

• with robotics and shielding due to radioactivity

- only small quantities desired

Question 15

properties of positron emitting radio tracers for PET scan

Answer 15

• short half lives (expensive)
• low energy
• cyclotron required
• biological elements
  comm: 18FDG

Question 16

what problems are there with tracer distribution?

Answer 16

short half lives need delivering quickly, or ideally a cyclotron on site making tracers expensive for PET

Question 17

what does PET stand for?

Answer 17

positron emission tomography

Question 18

what does SPECT stand for?

Answer 18

single photon emission computed tomography

Question 19

what are the principles of radionuclide imaging?

Answer 19

1) small amounts of molecules labelled with radionuclide
2) radiotracer administered to person
3) signal detected of radionuclide decay
4) convert signal to image

Question 20

describe how molecules are labelled with radionuclides?

Answer 20

• radiotracer amounts are are v small, half life is low, pure (radionuclide at one molecule)
• radionuclide is pure, no other ways of decay

Question 21

describe how radiotracer administered to biological system?

Answer 21

-all tracer molecules travel quickly to the abnormal area and stay

Question 22

how is the signal of the radionuclide decay detected?

Answer 22

• emitted particle should pass through the body, arriving at the detector in a predictable manner
• detector can discriminate each decay event

Question 23

how do the gamma photons go from patient to electrical pulse?

Answer 23

• collimator absorb non parallel photons
• scintillator crystal absorbs gamma photons
• scintillation emits optical photons that are converted to electrical current by photocathode in PMT

Question 24

how does scintillation work?

Answer 24

• gamma photons ejects electrons by e- (compton/photoelectric)
• when electron is excited then relaxed, visible light photon emitted
• NaCL doped with thallium crystal material

Question 25

describe a problem with light photons travelling from scintillation crystal to PMT photocathode

Answer 25

if their is air/solid interface TIR occurs so SI grease of similar optical index to crystal and cathode used

Question 26

How does the PMT (photomultiplier tube) work?

Answer 26

light hits photocathode producing e-, e- attracted to dynode gaining energy from ascending voltages. result is amplified electric signal

Question 27

what is a block detector?

Answer 27

cuts in scintillator crystal to distribute light between PMT, cost effective and solution to reading out scintillation light from large number of small crystals

Question 28

how does the pulse height analyser exclude scatter?

Answer 28

don't want badly positioned counts, so an energy limit applied within a percentage of the radioisotope energy

Question 29

how does the collimator work?

Answer 29

parallel lead bars absorb photons that will negatively impact the image

Question 30

how does the septal thickness of the collimator effect the image

Answer 30

septa must be thick enough to stop radiation with energy of imaged isotope. increasing thickness increases the imaging energy of photons that can pass, however this decreases sensitivity

Question 31

how does the hole depth of the collimator effect image

Answer 31

increasing the hole depth is increases resolution but decreases the sensitivity

Question 32

how does the hole size of the collimator effect the image?

Answer 32

- decreasing the hole size increases resolution | - smaller holes means more are of lead septa so sensitivity decrease

Question 33

how does the collimator to patient distance effect image?

Answer 33

larger collimator to patient distance increases the amount of noise effecting image

Question 34

what is the attenuation decay equation?

Answer 34

I=I0 exp(-ux) | u=attenuation coefficient

Question 35

describe image reconstruction with the analytical approach? adv and dis

Answer 35

- projects backwards the data with filter - fast, linear, well known - low resolution, streak artefacts

Question 36

describe image reconstruction using the iterative approach? adv and dis

Answer 36

- model measurement and integrating filtering - high resolution, visually better images - slow, stopping criteria, salt and pepper noise