Calculate the contrast of the sphere

Calculate activity qustions. See the attatchment

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J. A 1.0 cm diameter sphere (to simulate a tumor) is placed inside a20 cm diameter, cylindrical phantom (total volume of 6 L). The sphere is filled with water containing 1.0 MBq of Tc-99m. The phantom is also filled with a Tc-99m water solution, but with an activity of 850 Mbq. a) Calculate the contrast of the sphere. This would represent the contrast seen in a SPECT image. (2 marks) Now consider the imaging set-up shown in the figure. The detector acquires a lD image along x that is I cm thick in the z-direction. The sphere is located at a distance of (x, y) : (5 cm, 5 cm) from the centre of the phantom. The sphere is centered in the camera, with regard to the zdirection. The centre of the phantom is a distance of 30 cm from the imaging plane. The resolution of the scanner (including effects from all sotuces, i.e. collimator, crystal, etc.) is 12 mm @WHW). Assume an ideal, parallel-hole collimator. b) Neglecting l/f and attenuation artifacts, plot the relative counts, as a function of x, as seen on the detector. Assume perfect resolution. Calculate the contrast of the sphere in the image. Why does this contrast differ from that found in a)? (4 marks) c) Repeat b), but now include llf and attenuation affects. How do the recorded counts and calculated contast differ from that found in b)? Explain the differences. (4 marks) d) Redo c), but this time, include the effects of resolution. Label and explain the differences between the two sketches. (2 marks) e) Is there any location within the phantom that the sphere could be placed which would improve contrast? Explain. (2 marks) f) If noise is added to the image, would you expect the contrast from d) to change? Explain. (2 marks) detector a *ly –


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