Download Chapter 24 Radioactivity and nuclear magnetic resonance in medicine

CHAPTER 24 RADIOACTIVITY AND NUCLEAR MAGNETIC
RESONANCE IN MEDICINE
Name:
QUESTIONS
24.1 Radioactivity in medicine
1.
Write equations, as in the examples above, for the decay of:
(a)
americium-241 by alpha particle emission
(b)
uranium-238 by alpha particle emission
(c)
iridium-192 by beta particle emission
(d)
phosphorus-32 by beta particle emission.
2.
Thallium-201 has a half-life of 3 days. What percentage of an original sample will remain
after 12 days?
3.
Technetium-99m has a half-life of 6 hours. The original sample contained 2 mg of
technetium-99m. How long until only 0.25 mg of technetium-99m remains?
4.
Iodine-131 has a half-life of 8 days. How long will it take for the activity of iodine-131 to
drop from 10 MBq to 0.313 MBq?
5.
Summarise as a series of points the steps needed to obtain an image of an organ using a
radioisotope.
6.
Outline the function of the following parts of a gamma camera.
(a)
Lead collimator
(b)
Sodium iodide crystal
(c)
Photomultipliers
© John Wiley & Sons Australia, Ltd
1
QUEENSLAND PHYSICS
7.
Write an equation for the decay by positron emission of:
(a)
fluorine-18
(b)
oxygen-15.
8.
Summarise in point form the processes that occur when a PET scan is made.
9.
‘PET scans measure functional rather than structural information.’ What does this
statement mean?
10. In a table, compare SPECT with PET for imaging the brain.
11. Outline why alpha and beta emitters can be used for internal radiotherapy.
Review questions
Understanding
1.
Carbon-11 has a half-life of 20 min while bromine-75 has a half-life of 100 min. If
samples of these isotopes initially have the same activity, show on the same graph how
their activities vary with time.
2.
(a)
Outline two reasons why the hydrogen nucleus is imaged more than other nuclei in
MRI.
(b)
When protons are in a strong magnetic field they can occupy one of two possible
energy states. Describe these energy states and state which is the higher of the two.
(c)
Describe in what sense the MRI technique is nuclear.
3.
Explain why artificial metal joints between bones and metal fillings in teeth are a
problem with MRI.
4.
‘Medical physics has produced a wide range of harmless techniques that avoid the use of
invasive surgery.’ Evaluate this statement.
Application
5.
A small amount of iodine-131, which has a half-life of 8 days, is used to treat a patient
with a thyroid condition. Sixteen days later, an amount of 6.0 mg remains.
(a)
How much iodine-131 was used in the treatment?
© John Wiley & Sons Australia, Ltd
2
QUEENSLAND PHYSICS
6.
(b)
How much of the radioisotope will remain after another 16 days?
(c)
When is iodine-123 preferred to iodine-131 even though it is more expensive?
A sample of a radioisotope has a half-life of 2.0 minutes.
(a)
Calculate the time it will take the activity to drop from 4.0 MBq (megabecquerels)
to 1.0 MBq.
(b)
Calculate the time it will take for its activity to be 0.25 MBq.
7.
A particular isotope has a half-life of 100 days. Discuss the suitability of this isotope for
use in medical diagnosis.
8.
Describe the problems associated with using a radioisotope of very short half-life for
medical diagnosis.
9.
(a)
Choose two specific radioactive isotopes used in medical diagnosis and outline
where they would be used in the body. Justify your answer.
(b)
Explain why -emitting radioisotopes are not used for medical imaging.
10. Identify a radioactive tracer study in which the tracer:
(a)
mixes with the substance under investigation
(b)
is accumulated in the organ of interest.
11. Explain why technetium-99m is such an ideal radioisotope for medical imaging.
12. How are the radioisotopes used in PET scans different from those that are not used in
PET scans?
13. (a)
What is a positron?
(b)
How are positrons obtained?
(c)
Identify issues associated with positron−electron interaction and describe how this
interaction is used in medical diagnosis.
14. Figure 24.11 shows two different types of studies of lungs.
(a)
Contrast the studies.
© John Wiley & Sons Australia, Ltd
3
QUEENSLAND PHYSICS
(b)
Relate the type of study to the disease diagnosed.
15. Figure 24.9 shows an X-ray of a leg and a bone scan of the body.
(a)
Compare the X-ray image with the bone scan.
(b)
Explain why there are differences in the images obtained.
Challenge
16. The function of the lungs can be studied using a radioactive gas. The choices are
xenon-133 or krypton-81m and their properties are listed in the table below. Evaluate the
claim that ‘Xenon should be used in preference to krypton for investigations of lung
function’.
Notes:
© John Wiley & Sons Australia, Ltd
4