Medical Physics - exam practice

A radiographer in a hospital directs a parallel beam of X-rays at the leg bone of a patient. The attenuation (absorption) coefficient of bone is 0.7 cm^-1.

The answers below are given to one significant figure.

What is the percentage intensity of X-rays transmitted through bone of thickness 9.7 cm?

The Doppler effect is used to measure the speed of blood flow in arteries.

What medical diagnostic method uses this technique?

Ultrasound is reflected at a boundary between two materials.

Which property of the materials governs the intensity of the ultrasound reflected at the boundary?

A contrast material is used while taking an X-ray image of a patient.

Which statement is correct?

There are four important attenuation mechanisms by which X-ray photons may interact when they pass through matter.

In which mechanism is the X-ray photon scattered with a longer wavelength?

The acoustic impedance Z of a material in the shape of a cube can be determined using the equation $Z=\frac{Mc}{L^3}$

Where M is the mass of the material, L is the length of each side of the cube and c is the speed of ultrasound in the material.

The percentage uncertainty in L is 1.2 % and the percentage uncertainty in c is 1.8 %. The percentage uncertainty in M is negligible.

What is the percentage uncertainty in Z?

The potential difference across the cathode and anode of an X-ray tube is V. The minimum wavelength of the X-ray photons emitted from the tube is ${\lambda }_0$.

Which of the following statements is / are correct?

1. ${\lambda }_0$ is halved when V is doubled.
2. ${\lambda }_0$ is unchanged when the temperature of the cathode is increased.
3. ${\lambda }_0$ is independent of the cathode material.

Which is not a component used in a gamma camera?

A beam of ultrasound is incident normally at a boundary between two tissues F and G.

The table shows some data on the two tissues.

What percentage of the intensity of the ultrasound is reflected at the boundary?

What is the SI unit for acoustic impedance?