Medical Physics - exam practice
Medical Physics
Question 1 of 5
This question is about the use of ultrasound in medical imaging.
Explain how an ultrasound transducer can emit ultrasound.
Explain what is meant by impedance (acoustic) matching and how it may be achieved.
Explain how the reflection of ultrasound at a boundary between two tissues depends on the physical properties of the tissues.
This question is about the use of X-rays in medical imaging.
Describe the structure of an X-ray tube and explain how X-ray photons are produced.
X-rays used in hospitals have an energy of around 105 eV.
State the attenuation mechanism for these photons.
Calculate the minimum energy of a photon that is attenuated by the method in part b). Give your answer in eV.
Calculate, in terms of the incident intensity I0 of the X-ray beam, the intensity after passing through 3 cm of soft tissue. Soft tissue has an attenuation coefficient of 9.90 cm-1.
This question is about the attenuation of x rays.
Describe how x-rays are produced.
An X-ray of intensity I0 is incident on material A.
When the X-rays emerge from material B, they have an intensity I.
The attenuation coefficients of A and B respectively are 0.6 cm-1 and 0.4 cm-1.
Calculate the value of if the intensity of the emerging X-rays is 0.1653 I0.
State what is meant by the contrast of an X-ray image.
Magnetic resonance imaging is one method of visualising internal body structures.
Explain the principles of nuclear magnetic resonance imaging (NMRI) to obtain information about internal body structures.
Radioactive isotopes are used in medical imaging.
Fluorine-18 is a radioactive isotope used in positron emission tomography (PET).
A patient is injected with a radiopharmaceutical containing fluorine-18.
Describe how a PET scanner is used to locate an area of increased activity within the patient.
The decay constant of fluorine-18 is 1.05 x 10-4 s-1.
Calculate the time in minutes for the activity of the radiopharmaceutical to decrease to 15% of its initial activity.
Suggest one reason why PET scanners are not available in all hospitals.