A-LevelPhysicsMedical physics9702/42 · May/June 2018 · Q117 Marks
Describe the basic principles of CT scanning (computed tomography).
- (a)Describe the basic principles of CT scanning (computed tomography).[5]
- (b)(i)By reference to your answer in (a), suggest why CT scanning was not possible before fast computers with large memories were available,[1]
- (b)(ii)the radiation dose for a CT scan is much larger than for an X-ray image of a leg bone.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- [M1] X-ray image(s) taken of one slice
- [A1] (many images) taken from different angles
- [B1] (computer) produces 2D image of slice
- [M1] (this is) repeated for (many) slices
- [A1] to build up a 3D image (of structure)
- [B1] combining of images involves (very) large number of calculations
- [B1] CT scan consists of (very) many (single X-ray) images
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