'A' Level Medical Option Questions - X-Rays
(a) When an X-ray image is obtained of certain organs, image contrast enhancement is necessary. Explain why image contrast enhancement is needed and describe how this might be achieved.
For a clear image you need a large difference in densities between part being investigated and parts around it. When this is not natural, you can add material to the part under investigation which has high density to provide good attenuation of X-rays An example of a suitable contrast material for a barium meal is barium sulfate
(b) A monochromatic X-ray beam of intensity 3.2 × 10–2 W m–2 is incident on an aluminium sheet. Calculate the thickness of aluminium required to reduce the intensity of the X-ray beam to 1.2 × 10–2 W m–2.
mass attenuation coefficient of aluminium, m = 0.012 m2 kg–1
density of aluminium, = 2700 kg m–3
= 2700 x 0.012
= 32.4 m-1
I = Io e-x
1.2 × 10-2 = 3.2 x 10-2 x e-32.4x
x = 0.030 m
(Total 6 marks)