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An explanation of the principles behind x-ray imaging, focusing on the role of scanning lines, objects, and filters. How objects represent pixels, the number of lines required for adequate resolution, and the importance of filters in removing low-energy radiation. It also mentions the historical context of roentgen's discovery of x-rays.
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Figure 12.1 Scanning lines and round objects (a) Each object represents 1 pixel, but each cycle of output signal represents 2 pixels. (b) For 2 n scanning lines, n vertical objects are required. (c) If objects are located between scanning lines, 2 n lines are insufficient. (d) For adequate resolution, 2 n √2 lines are required. © From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 12.2 In each successive gamma-camera picture of a thyroid phantom, the number of counts is increased by a factor of 2. The number of counts ranges from 1563 to 800,000. The Polaroid camera aperture was reduced to avoid overexposure as the number of counts was increased. © From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 12.6 The x-ray tube generates x rays that are restricted by the aperture in the collimator. The Al filter removes low-energy x rays that would not penetrate the body. Scattered secondary radiation is trapped by the grid, whereas primary radiation strikes the screen phosphor. The resulting light exposes the film. © From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 12.7 The lowest-energy x rays are absorbed in the anode metal and the tube glass envelope. An Al filter further reduces the low-energy x rays that do not pass through the body and would just increase the patient dose. Only the highest-energy x rays are capable of penetrating the body and contributing to the film darkening required for a picture. Note that the average energy increases with the amount of filtration. © From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
