Medical imaging

Question 1

How does a gamma camera work in a flow chart?

Answer 1

1. Radionuclide attached to a compound so it can be absorbed by organ of interest.
2. Patient given nuclear tracer. After some time, patient placed in front of gamma camera. Gamma rays exit patient body.
3. Collimator only allows gamma rays to pass at a particular angle so a sharper image can be formed.
4. Gamma rays hit detection crystals and scintillate.
5. Photomultiplier tubes electronically increase/ amplify intensity of light produced.
6. These are now able to be picked up by light sensors. They pass the data to electronics and computers to then process an image.

Question 2

How does an MRI scan work?

Answer 2

1. Electromagnetic field causes the spin of protons in water to align to its direction. (High H2O content good for viewing with MRI)
2. Radio frequency causes protons to resonate (excite and precess further)
3. When radio frequency ends, protons de-excite and release a radio signal.
4. The signal, as well as relaxation time, is picked up by the receiver coils.

(The change in precession from near 90 degrees back to normal (because of magnet) is picked up by receiver coils to process an image.)

Question 3

Explain how medical imaging is done with nuclear isotopes.

Answer 3

1. The suitable radiotracer is attached to a compound so it can be absorbed by the organ of interest.
2. Availability, chemical versatility, penetration, activity (not too high/low) and half-life (not too high/low) are the factors.
3. I2 used for thyroid scans as the thyroid absorbs iodine naturally.
4. Tc-99m used in bone scans. Gamma rays it emits can be picked up by gamma cameras to diagnose diseases (brain, heart, liver, kidneys, lungs, bone).
5. They have short half-lives (physical and biological) and can be given by injection, inhalation or orally.