24.3. PET scanning
A subsection of Physics, 9702, through 24. Medical physics
Listing 10 of 11 questions
Positron emission tomography (PET scanning) obtains diagnostic information from a person. The information is used to form an image. PET scanning uses a tracer. Explain what is meant by a tracer. PET scanning involves annihilation. Explain what is meant by annihilation. State the names of the particles involved in the annihilation process. Calculate the total energy released in one annihilation event in . energy = J Calculate the wavelength of each gamma photon released. wavelength = m Explain how the gamma photons are used to produce an image.
9702_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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Positron emission tomography (PET scanning) involves the detection of gamma-radiation in order to identify the position of origin of positrons in the body. Positrons are not naturally present in the body. Explain how positrons come to be present in the body during PET scanning. Explain how positrons cause the emission of gamma-radiation from the body during PET scanning. Show that the wavelength of the gamma-radiation that is detected during PET scanning is approximately 2.4 pm. Explain your reasoning.
9702_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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Fluorine-18 (18 9F) is a radioactive nuclide that is used as a tracer in positron emission tomography (PET scanning). Fluorine-18 decays to a nuclide of oxygen (O) according to 9F Q P X + R 8O. State what is meant by a tracer. State the symbol of the particle that is represented by X and the values of P, Q and R. X: P: Q: R: Explain how the radioactive decay of fluorine-18 results in the emission from the body of the gamma-ray photons that are detected during a PET scan. Explain how the detection of the gamma-ray photons is used to produce an image of the tissue being examined. The half-life of fluorine-18 is T. A patient is injected with amount of substance n of fluorine-18. Determine an expression for the initial value R0 of the rate R of production of gamma-ray photons by the tracer, in terms of n, T and the Avogadro constant NA. R0 = On , sketch the variation with time t of R. R0 R 0 T t
9702_w23_qp_42
THEORY
2023
Paper 4, Variant 2
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Fluorine-18 ( 18 9F) decays by beta-plus (β+) emission with a half-life of 110 minutes. State the name of the beta-plus particle. Show that the decay constant of fluorine-18 is 1.05 × 10–4 s–1. Determine the activity of 2.1 × 10–12 kg of fluorine-18. activity = Bq A small sample of fluorine-18 injected into the body acts as a tracer for use in medical imaging. Describe how the interaction of a β+ particle with an electron in the body enables the formation of an image. Suggest why 110 minutes is a suitable half-life for a nuclide used as a tracer in medical diagnosis.
9702_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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Fluorine-18 ( 18 9F) decays by beta-plus (β+) emission with a half-life of 110 minutes. State the name of the beta-plus particle. Show that the decay constant of fluorine-18 is 1.05 × 10–4 s–1. Determine the activity of 2.1 × 10–12 kg of fluorine-18. activity = Bq A small sample of fluorine-18 injected into the body acts as a tracer for use in medical imaging. Describe how the interaction of a β+ particle with an electron in the body enables the formation of an image. Suggest why 110 minutes is a suitable half-life for a nuclide used as a tracer in medical diagnosis.
9702_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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A parallel beam of electrons, all travelling at the same speed, is incident normally on a carbon film. The scattering of the electrons by the film is observed on a fluorescent screen, as illustrated in . Assuming that the electrons behave as particles, predict what would be seen on the screen. In this experiment, the electrons do not behave as particles. Describe briefly the pattern that is actually observed on the screen. You may draw a sketch if you wish. Use carbon film beam of electrons glass envelope fluorescent screen vacuum [T The speed of the electrons is gradually increased. State and explain what change, if any, is observed in the pattern on the screen.
9702_s06_qp_4
THEORY
2006
Paper 4, Variant 0
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A positron ( 0 +1e ) is a particle that has the same mass as an electron and has a charge of +1.6 × 10–19 C. A positron will interact with an electron to form two γ-ray photons. +1e + 0 –1e → 2 γ Assuming that the kinetic energy of the positron and the electron is negligible when they interact, suggest why the two photons will move off in opposite directions with equal energies, calculate the energy, in MeV, of one of the γ-ray photons. energy = MeV
9702_s08_qp_4
THEORY
2008
Paper 4, Variant 0
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Explain what is meant by gamma radiation (γ-radiation). A source of gamma radiation is placed a fixed distance away from a detector and counter, as illustrated in . [ GHWHFWRU VKLHOGLQJ VRXUFH OHDGVKHHW WRFRXQWHU A sheet of lead of thickness x is placed between the source and the detector. The average count rate C, corrected for background, is recorded. This is repeated for different values of x. The variation with thickness x of ln C is shown in . The value of μ calculated in is for gamma radiation in lead. Suggest and explain whether the value of μ for aluminium would be the same, greater or smaller.
9702_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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An electron, at rest, has mass me and charge –q. A positron is a particle that, at rest, has mass me and charge +q. A positron interacts with an electron. The electron and the positron may be considered to be at rest. The outcome of this interaction is that the electron and the positron become two gamma-ray (γ-ray) photons, each having the same energy. Calculate, for one of the γ-ray photons: the photon energy, in J energy = J its momentum. momentum = N s State and explain the direction, relative to each other, in which the γ-ray photons are emitted.
9702_s20_qp_41
THEORY
2020
Paper 4, Variant 1
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An electron, at rest, has mass me and charge –q. A positron is a particle that, at rest, has mass me and charge +q. A positron interacts with an electron. The electron and the positron may be considered to be at rest. The outcome of this interaction is that the electron and the positron become two gamma-ray (γ-ray) photons, each having the same energy. Calculate, for one of the γ-ray photons: the photon energy, in J energy = J its momentum. momentum = N s State and explain the direction, relative to each other, in which the γ-ray photons are emitted.
9702_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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Questions Discovered
11