pet scan / astronomy

Question 1

tracer

Answer 1

substance introduced into the body and it is absorbed by tissue being studied which emits e+ particles

Question 2

role of Fluorine-18

Answer 2

• medical tracer used in position emission tomography
• half life of 110 mins (good cuz ↓er radiation exposure)
• (use) : 18/9 F –> 18/8 O + 0/1 e + 0/0v + Y
• (production) : has to be made on-site/lab with particle accelerator.
  ↑ speed proton collides w O-18 to produce F-18 and 0/1 N
  18/8 O + 1/1 p –> 18/9F + 1/0 n

Question 3

role of FDG

Answer 3

• radioactive tracer similar to naturally occurring glucose but is tagged w radioactive F-18 and oxygen atom

Question 4

adv of FDG

Answer 4

• taken up at different rates by diff tissues or organs.

- cancer cells r more active than surrounding cells, and absorb glucose at ↑er rate & emit radiation at a ↑er rate

Question 5

Outline principles of PET scanner

Answer 5

• tracer with positron emitter as tag
• when positron meets an e- in tissues, annihilation of positron-electron pair takes place
• pair of gamma rays w same magnitude of momentum is produced, and they travel at 180° to each other in order to conserve momentum
• the y rays strike detector and line of response is established
• the point at which interaction took place determined by arrival time

Question 6

explain what is meant by ‘line of response’ and how it is used to identify the precise site of cancerous tissue

Answer 6

• line of response is a straight line btw 2 detectors detecting y rays produced by annihilation event
• the precise position of the annihilation event is on this line and is calculated from the time difference btw the arrival of the 2 y-rays produced in the event

Question 7

explain what is meant by an ‘annihilation event’ with ref to PET scanning and name the important quantities which are conserved in an annihilation event.

Answer 7

• when a particle and its anti-particles meet, they annihilate each other and emit a pair of y-rays which travel at 180° to each other
• the quantities which are conserved are mass-energy and momentum

Question 8

In 1 type of PET scanner, the tracer isotope is Rb-32. Write an eqn for the decay of this isotope

Answer 8

82/37 Rb –> 0/1 e + 0/0 v + Y + 82/36Kr

Question 9

state the name of particles emitted from body nd detected by detectors during PET scanning

Answer 9

gamma photons

Question 10

explain how gamma photons are created from positrons

Answer 10

• positron emitted meet w e- in the tissue
• annihilation takes place
• positron is anti-particle of e-
• gamma ray is produced

Question 11

disadv of PET

Answer 11

• expensive as facilities on found in large hospitals

Question 12

adv of PET

Answer 12

• non invasive technique (no surgery/break in skin required)
• used to help diagnose diff types of cancers, as it helps to plan complex heat surgery and observe function of brain
• helps assess the effect of new meds and drugs on organs

Question 13

Positrons are artificially created by a process in the lab, producing a positron and e- moving w same speed in the same directions.
- Suggest why 2 of the gamma photons required to create 1 positron

Answer 13

• positrona and e- have same mass.
• combined momentum of positron and e- is 0
• since gamma rays have the same magnitude of momentum but in opp directions, they can be used to produce positron and electron in order to conserve momentum

Question 14

annihilation

Answer 14

a particle interacting w its anti-particle so that mass is converted into E

Question 15

exp how gamma photons are used to produce an image

Answer 15

• the 2 y photons travel in opp directions
• the no. of photons arriving from a particular point determines the conc of the tracer at that point
• when there’s many photons arriving at the same time, this means that there is a ↑ conc of tracer
• bright spot on image in shown

Question 16

luminosity

Answer 16

total power of radiation emitted by the star