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Nuclear Medicine and Radiation Safety: Quiz

Seven questions on radiation units, medical isotopes, PET and radiation protection, with explanations.

7 questionsIntermediate

7 questions

  1. Question 1EasyWhich unit measures the energy absorbed per kilogram of tissue?
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    Answer: gray

    1 Gy = 1 J/kg. The becquerel measures activity; the sievert adds the radiation weighting factor.

  2. Question 2EasyWhich isotope is best suited to imaging an organ?
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    Answer: a gamma emitter with a half-life of 6 hours

    Gamma rays leave the body to reach the camera, and a short half-life limits the dose. This describes technetium-99m.

  3. Question 3MediumAn absorbed dose of 0.010 Gy from alpha particles gives an equivalent dose of:
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    Answer: 0.20 Sv

    Equivalent dose = 0.010 Gy × 20 = 0.20 Sv.

  4. Question 4MediumThe dose rate at 1.0 m is 36 µSv/h. What is it at 3.0 m?
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    Answer: 4.0 µSv/h

    36 µSv/h × (1.0 m ÷ 3.0 m)² = 36 µSv/h ÷ 9 = 4.0 µSv/h.

  5. Question 5MediumIn a PET scan, what is detected?
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    Answer: two gamma rays travelling in opposite directions

    Positrons annihilate with electrons inside the body, producing pairs of 511 keV gamma rays at 180°.

  6. Question 6HardA shield has a half-value thickness of 2.0 mm. What fraction of the gamma rays passes through 6.0 mm?
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    Answer: 1/8

    6.0 mm ÷ 2.0 mm = 3 half-value thicknesses, so (½)³ = 1/8 gets through.

  7. Question 7MediumWhy is iodine-131 used to treat the thyroid?
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    Answer: the thyroid takes up iodine, and its beta particles destroy nearby tissue

    Chemistry delivers the isotope to the right organ; the short-range beta particles deposit their energy there.