Question T 11 marks a) Usc the information given in the graph in Figure A below

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Question T 11 marks a) Usc the information given in the graph in Figure A below to cxplain why an X-ray beam with an avcrage photon encrgy of 0.05 MeV would produce a more effective X-ray image of a mixture of bone and tissuc than a beam with an avcrage encrgy of 0.10 McV Figure A Graph of the % of attenuation that occurs via Compton scattering as a function of X- ray photon cncrgy for bonc and tissuc 100% 90% 80% 70% 60% 50% Tissue Compton % of total attenuation l 40% 30% 20% 10% 0% 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 photon energy (Mev) Use the information in the following graph in Figure B to help you to explain why using a thin sheet of aluminium to remove X-ray photons with energy less than 0.01 MeV from an X-ray beam with average encrgy of 0.05 MeV would result in a lower doe to the patient while still producing an adequate image of bone and muscle. (b) 500 Figure B Graph of the total attenuation coefficient as a function of TotalE 450 attenuation coefficient X-ray photon energy for bone and tissue (m350 300 250 200 Bone 100 50 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 photon energy (Mev) (c) The attenuation coefficients for 0.05 MeV X-ray photons passing through blood and tissue are very similar so blood vessels are difficult to image. Bricfly describe one technique that could be used to produce an excellent X-ray image of a blood vessel embedded in tissue and explain why it would be effective. [4+4+3= 11 marks ] End of examination questions; Equations and data sheet follows. PHYC10006, Semester 2 2014, Page 11 of 13

Explanation / Answer

(a) The difference between the attenuation of tissue and bone at X-ray energy 0.1 MeV is around 15%, but that of the X-ray energy 0.05 MeV it is around 50%

Hence the variation of compton scattering will lead to a better contrast in the X-ray image involving bone and tissue. This leads to sharper looking images increasing contrast.

(b) The value of attenuation due to tissue is very high for X-ray photons with energies less than 0.01 MeV. This leads to high dose deposition through the tissue. The thin sheet of aluminium would absorb most of the photons below 0.01 MeV, This leads to lesser dose while maintaining the contrast between tissue and bone.

(c) As attenuation coefficients of 0.05 MeV X-ray photons for blood and tissue are similar, it is difficult to obtain images with contrast. One technique to overcome this, is to use contrast agents. Iodine (Z=53), and Barium (Z=56) based compounds are used to administered and improve contrast of the blood vessel embedded in tissue. The attenuation due to these high atomic number (Z) elements within the blood vessel will be much higher compared to background tissue. Hence this method is effective to distinguish and produce good contrast images.

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