Radiopharmaceutical

Question 1

What is Alpha, beta and gamma?

Answer 1

Alpha is composed of 2 protons and 2 neutrons - not very penetrating but highly ionising

A beta is an electron - partially penetrating and ionising

A gamma is energy - most penetrating low ionising.

Question 2

Describe how nuclear medicine can be used for therapy and imaging

Answer 2

Therapy

Label pharmaceutical with alpha or beta emitter to be absorbed locally at tumour/target site e.g. Radium-223 dichloride (Xofigo TM).

Imaging

Label pharmaceutical with gamma emitting radionuclide which can escape from body e.g. Technetium-99m phosphonates (bone imaging)

Question 3

The Gamma Camera

Answer 3

Question 4

The collimator

Answer 4

Provides positional information. Only ionising radiation parallel to the collimator holes are allowed through to the scintillation crystal

Question 5

Scintillation Crystal

Answer 5

Ionising radiation creates light photons

Question 6

Photomultipler Tubes

Answer 6

Light photons are converted into electrons and then significantly amplified in number

Question 7

Processing Electronics

Answer 7

Positional and energy information is gathered. Image is digitised ready for display

Question 8

The tracer principle

Answer 8

A trace amount of active pharmaceutical that follows the pharmacological pathway without affecting physiology.

Question 9

Basis of Radionuclide Imaging

Answer 9

Measures the pathway of a Drug in the body

– Where, How Much, How Fast?

Detect Abnormalities unexpected Distribution

Measure Physiology by Uptake (Kinetics)

Achieved by:

– Labelling the drug with a Radioactive Material

– Collecting the Emissions from this Material

Question 10

How does radionuclide imaging compare with X-Ray imaging?

Answer 10

• Measures Function not Structure
• Image Contrast Due to Uptake not Attenuation
• Radiation Source is inside the Body and not Outside
• Radiation Emission Position and Detection Unknown
• Radiation Energy Known (Energy Ranges Similar)
• Radiation Flux Much Lower
• Radiation Emitted Before, After and During Imaging
• Harder to Correct for Scattered Radiation

Question 11

what does 131 and 53 mean?

Answer 11

Question 12

What values of Z are stable and not stable?

Answer 12

high values of z.

Question 13

Unstable nuclei emission?

Answer 13

Question 14

Describe Beta minus decay?

Answer 14

Excess of Neutrons

• Conversion to proton, negative beta particle (electron), and neutrino
• Beta particles ejected at very high velocities with a range of energies (up to a finite maximum)

– Z → Z + 1 Atomic number increases by 1

– N → N - 1 Neutron number decreases by 1

– A → A Mass number is unchanged

Question 15

Beta Plus (Positron) Decay

Answer 15

• Excess of Protons
• Conversion to neutron, positive beta particle (positron), and neutrino
• Beta particles ejected at very high velocities with a range of energies (up to a finite maximum)

Z → Z - 1 Atomic number decreases by 1

– N → N + 1 Neutron number increases by 1

– A → A Mass number is unchanged

Question 16

electron capture mechanism?

Answer 16

p + e- → n + v

• excess protons leads to k-shell electron to be captured by a proton
• neutrobn and neutrino created during the transformation
• outer electron falls into vacant orbit

X-ray emitted with energy determined by the transition energy ΔE = hv

where h = plancks constant and v = frequency

Z → Z - 1 Atomic number decreases by 1

– N → N + 1 Neutron number increases by 1

– A → A Mass number is unchanged

Question 17

alpha decay mechanism?

Answer 17

2p + 2n -> α

Natural Radioactive elements heavier than Lead

Ejection of an alpha particle (Helium nucleus)

Z → Z - 2 Atomic number decreases by 2

N → N - 2 Neutron number decreases by 2

A → A - 4 Mass number decreases by 4

Question 18

gamma decay?

Answer 18

• Gamma ray emission only happens after previous beta or alpha emission.
• Many parent radionuclides go to a ‘metastable’ state through beta or alpha emission.
• Metastable daughter loses excess energy as a gamma photon to revert to ground state
• Most common radionuclide i n muclear medicine is a metastabkle isotope (Tc-99m)
• No change in mass or atomic number using this type of decay.

Question 19

What is used in Positron Emission tomography

Answer 19

Beta plus (positron) decay

• positron has tortuous path, with several interactions,

It eventually annihilates with an electron

2 x 511 keV photons (180 degrees to eachother)

Question 20

Decay scheme for Tc-99m?

Answer 20

The nucleus is in a metastable state and the ground state are different isomers. The decay of 99mTc to 99Tc is an example of an isomeric transition.

Question 21

Ideal imaging characteristics

Answer 21

Radiation type

• XRAY or gamma

Photon energy

• ideally 120-180keV

Half life

• Depends on uptake rate - normally hours

Question 22

what is the decay equation?

Answer 22

N – no Atoms of a particular Radioactive material

dN – change in no. Atoms

dt – change in time

λ – the transformation constant

Question 23

equation for activity?

Answer 23

A = -dN / dt

Question 24

define Half life?

Answer 24

Defined as the time required for half the atoms to decay.

The activity is also reduced by half in this time.

Question 25

Answer 25

Question 26

Answer 26