ABSTRACT
K-edges are in the diagnostic range b. Intensifying screens utilize thermoluminescence c. Up to two intensifying screens might be used d. Characteristic curves are plotted with OD against exposure e. Film gamma is measured as the average slope of the characteristic
curve
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19. has an OD of 0.5 high gamma will have a
relatively wide latitude c. Ideally an intensification screen should be as thick as possible d. A phosphor with greater X-rays to light conversion will be
associated with more noise than an equally sensitive phosphor with a lower conversion efficiency but a greater thickness
e. Crossover is impossible if a single side of film emulsion is used
20. Intensifying screens: a. Intensifying screens reduce dose but increase noise for the same
amount of film blackening b. Without an intensification screen, only about 20% of the X-ray
photons would be absorbed by the film c. Intensification factor is the ratio of kerma for a film density of
1 with and without the intensifying screen d. Rare earth screens are used because of their very high atomic
number e. A thicker phosphor layer decreases dose required at the expense
of greater noise and screen unsharpness
21. In mammography: a. A K-edge filter such as molybdenum is commonly used b. The filter should not be the same element as the anode target
otherwise the characteristic radiation would be absorbed c. Typical spatial resolution for both digital and film mammography
is 15 lp/mm d. Typical mean glandular breast dose is 1.5-3 mGy for a single
exposure e. Typical kV for mammography is 24-35 kV
22. With linear tomography: a. Blurring is deliberately introduced into the image through
movement b. The cut plane slice is centred at the pivot height c. The slice thickness is increased by increasing the angle of move-
ment of the tube and plate d. Zonography techniques image a very narrow slice thickness e. Contrast is typically lower in linear tomography compared to
conventional radiography because of the blurring of overlying tissues spread over the image
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23. alternating between a high
to allow the formation of a subtracted image that maximizes tissue contrast
b. For a given mA, soft tissue contrast will be increased by using a lower kV X-ray beam
c. Subtracting a low kV image from a high kV image will improve soft tissue contrast and minimize the visualization of bone
d. The detection of a calcified lung nodule could be improved by subtracting the low kV image from the high kV image
e. Dual energy digital subtraction angiography (otherwise known as DE DSA) is performed after an intra-arterial or intravenous injection of iodinated contrast medium
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1a. False Radio-opaque contrast media is chosen so that the high atomic number maximizes photoelectric absorption of the beam. The K-edge energy of the contrast medium should be slightly less than the major part of the X-ray energy spectrum to maximize this effect.
