Nuc Med

Question 1

What type of radionucelide is used for diagnostic purposes?

Answer 1

• Single photon emitters (planar imaging, SPECT)
• Positron Emitters (PET)

Question 2

What type of Radionuclide is used for therapeutic purposes?

Answer 2

• Beta minus emitters
• Augur emitters
• Alpha emitters

Question 3

what is an augur electron?

Answer 3

auguer e- are emitted with an atom undergoes the auger process - have low energies
1. atom is ionised by absorbing a photon - atom loses e-
2. another outer shell electron jumps down to fill the space and gives out auger e- instead of characteristic x-ray
3. another augur - can be emitted if the atom still have excess energy and it passes it onto another atom

Question 3

what is an augur electron?

Answer 3

auguer e- are emitted with an atom undergoes the auger process
- have low energies
- have short ranges in matter
1. atom is ionised by absorbing a photon - atom loses e-
2. another outer shell electron jumps down to fill the space and gives out auger e- instead of characteristic x-ray
3. another augur - can be emitted if the atom still have excess energy and it passes it onto another atom

Question 4

What factors are considered when looking at any radionucleide?

Answer 4

• Emission (gamma for diagnostics)
• Half life
• Energy of ray
• Complexity (not too many emissions - would add additional noise)
• chemical properties (can it be incorporated into another organic compound)
• ease of manufacture
• toxicity

Question 5

how is Tc-99m formed from 99Mo

Answer 5

1. Mo-99 is produced in a nuclear reactor
2. Mo-99 is extracted from target material, which is dissolved. Mo-99 is chemically isolated
3. Mo-99 is taken to pharmacy and loaded onto generator column made of an alumina material where the Mo-99 is aDsorbed
4. Mo-99 decays with a half-life of 66 hours and transforms into Tc-99m
5. When Tc is needed, a saline solution is passed through the generator column to selectively extracts the Tc only.

Question 6

How does a gamma camera work?

Answer 6

1. Collimator - shield with holes to let through only gamma rays that are perpendicular to the scanner. (Helps with spatial localisation) thicker lead can be used to prevent septal penetration but too much reduces sensitivity
2. Scintillation crystals - Nal doped with Tl. gamma rays deposit energy in crystal and release another e- which ionises other atoms. These e- move into valence spaces and give out flashes of light
   light guide to couple the crystal to PMT to minimise light loss and variation in collection
3. PMTs are sensitive to light and convert scintillation photons into electrical pulse which is then amplified using dynodes
4. Gamma camera moves around the pt and takes images from all angles
5. Data Acquisition System - The data acquisition system collects the electrical signals generated by the PMTs and digitizes the signals, records their positions, and measures their energies.
6. The signal goes to a computer where the data is reconstructed into a visual.

Question 7

What is the equation for a gamma camera collimator for resolution?

Answer 7

Rg ~ d(L+D)/L (D is distance from pt)
* Increase diameter – worse resolution
* Increase length – better resolution
* Increase distance from collimator – worse
resolution
(Rg)^2 = sensitivity

Question 8

What is the equation for a gamma camera for spatial resolution?

Answer 8

Combination of intrinsic resolution and extrinsic (collimator)
resolution
* Rs = √(Ri 2 + Rc 2)
Ri = intrinsic resolution, Rc = collimator resolution, Rs = system resolution

Question 9

What is intrinsic and extrinsic resolution linked to in terms of gamma camera components?

Answer 9

Intrinsic - Light Spread from crystals interactions
Extrinsic - Image blurring from collimator design, distance between pt and detector

Question 10

Is sensitivity of the gamma camera dependent on distance?

Answer 10

No (maybe scatter in air), only collimator geometry (compromise with resolution)

Question 10

Is sensitivity of the gamma camera dependent on distance?

Answer 10

No (maybe scatter in air), only collimator geometry (compromise with resolution)

Question 11

Count Rate Performance Equation

Answer 11

R = N e ^(-N tau) where tau = dead time

Question 12

Standards of Gamma Camera

Answer 12

Uniformity
Resolution (spatial and energy)
Linearity (spatial distortion)
Sensitivity (efficiency)
Count Rate Performance

Question 13

Gamma camera
- photo peak
- FWHM

Answer 13

• photo peak = 140 keV (+- 10%)
• FWHM = 18 keV

Question 14

causes for non-uniformity in gamma camera

Answer 14

• Crystal construction
• PMT gain
• Non-linearity in anger logic

Gamma camera can “correct” through the use of maps

Question 15

SPECT Benefits

Answer 15

• 3D localisation of source
• Improved quantification
• Background removal

Question 16

dose equation

Answer 16

dose rate x time = dose rate

Question 17

effective dose equation

Answer 17

Effective dose = sum(equivalent dose x tissue weighting factor) for all organs

(Equivalent dose is absorbed dose weighted for radiation type)

Question 18

S-factor

Answer 18

Dose from one organ (source) to another (target) for a specific energy or radionuclide

Question 19

Idea of cumulated activity and equation

Answer 19

• Total number of emissions from an organ during lifetime
  of radioactive material
• Area under time-activity curve
• 𝐴cumul = f . Ao / λeff
• where f is the fraction of the
  initial administered activity, A o ,
  within the source organ
• And λeff is the effective decay
  constant for the organ (physical
  and biological clearance)