X-ray Spectra and Medical Uses of X-rays
1.1 Describe two mechanisms for the production of Xrays and relate these to X-ray spectra (continuous and line spectra.)
1.2 Using a diagram describe the structure of an X-ray tube.
1.3 Describe the production of X-rays by a rotating anode tube.
1.4 Explain the importance of reducing exposure dose and time and describe mechanisms for achieving this.
1.5 Interpret graphs relating X-ray spectra to tube voltage, tube current and target material.
2.1 Define attenuation and explain attenuation of Xrays by scatter, the photo-electric effect, Compton scatter and pair production.
2.2 Describe how attenuation effects correlate with photon energy, transmission material and distance travelled.
2.3 Explain the significance of attenuation for conventional medical X-ray imaging.
3.1 Explain the principle of computer aided tomography and the advances that led to the development of the CAT scanner.
3.2 Explain the use of X-rays in radiotherapy.
Assignment Brief:
Question 1
There are two distinct components to an X-ray spectrum generated by an Xray tube — the braking radiation (Bremsstrahlung) and characteristic lines. The appearances of these two components depend on the nature of the tube and its operating conditions. Describe the features of these components relating them to the mechanisms by which they are produced.
Question 2
Draw and label a schematic diagram to show the structure of a basic X-ray tube.
Question 3
Describe the production of X-rays by a rotating anode tube. Explain the advantages of using a rotating anode compared to a fixed anode.
Question 4
Explain the importance of reducing exposure dose and time to a patient undergoing a diagnostic X-ray examination. Describe ways to achieve this.
Question 5
In the following spectra the solid line represents the original operating conditions of the X-ray tube and the dashed line represents the modified spectrum obtained after changing either tube voltage, tube current or target material.
Identify which of the spectra, a), b) or c) relate to each of the three kinds of change in operating conditions, and explain the physical processes leading to these modifications in the spectra.
Question 6
Define attenuation and explain attenuation of X-rays by simple scattering (Rayleigh), the photo-electric effect, Compton scattering and pair production.
[2.1]
Question 7
Describe how the attenuation of X-rays correlate with
i) their photon energy,
ii) the chemical make-up of the transmission material, and
iii) the distance they have travelled through the material.
[2.2]
Question 8
Explain how attenuation in conventional medical X-ray imaging leads to projection images of the patient and how the X-ray energy spectrum can be optimised to produce images with good contrast between tissues of different density.
[2.3]
Question 9
Explain the principles of computer aided tomography and the advances that led to the development of the CAT scanner.
[3.1]
Question 10
Explain the principles behind X-ray radiotherapy treatment of malignant tumours.
Describe how treatment is optimised to reduce damage to healthy tissue.
[3.2]
