Film Screen Q & A Robert Metzger, Ph.D. RAPHEX General Question 2001 D10: Flood replenishment of a processor involves all of the following except: A. Draining and refilling the developer tank each day. B. Putting starter solution into the replenishment tank. C. Replenishment of developer on a timed basis (e.g. every 15 min). D. Stabilization of sensitometry for low volume pressures. E. A possible compromise in film contrast. RAPHEX Answer to 2001 General Question D10 A. Flood replenishment uses timed replenishment to stabilize the processor in low film volume situations. It requires the addition of starter to the developer replenishment tank, which may not result in optimum processing of film. It does not involve daily draining. RAPHEX General Question 2001 D15: If the absorption efficiency of each intensifying screen in a dual screen system is 30%, what percentage of x-rays is stopped by the screens together? A. B. C. D. E. 9% 30% 51% 60% 70% RAPHEX Answer to 2001 General Question D15 C. 30% is absorbed in the first screen, 70% passes through. The second screen absorbs 30% of that 70% (or 21%). Total stopped is 30% + 21%. RAPHEX General Question 2003 D25: A radiograph with an optical density (OD) of 3.0. A. Transmits 1/3 times as much light as a film with an OD of 1.0. B. Has a combined OD of 6.0 when placed over another film of OD 2.0. C. Looks “light gray” on a standard view box. D. Transmits 0.1% of the light incident upon it. RAPHEX Answer to 2003 General Question D25 D. Optical densities are additive, so the net OD of both films is 5.0. An OD of 3.0 looks black on a standard view box. OD = log10(I/T), where I and T are the incident and transmitted light intensities. For OD = 3.0, T = 0.001, and OD = 1.0, T = 0.1. RAPHEX General Question 2001 G72: A radiograph transmits 10% of the light from a viewbox with an illumination level of 400 lux. The optical density of the radiograph is ________ . A. B. C. D. E. 10 2 1 0.1 1/400 RAPHEX Answer to 2001 General Question G72 C. Optical density (OD) = log (incident intensity / transmitted intensity) = log (1/0.1) = log10 = 1.0. RAPHEX General Question 2002 G75: A grid improves the quality of a diagnostic x-ray primarily by attenuating ________ . A. B. C. D. E. Primary photons Compton scattered photons Compton electrons Photoelectrons Coherent scattered photons RAPHEX Answer to 2002 General Question G75 B. Compton-scattered photons travel in random directions, and contain no useful diagnostic information. The grid absorbs most of these photons, and thus improves image contrast. RAPHEX General Question 2003 G80. There are approximately _______ bits in a megabyte. A. B. C. D. E. 1024 2048 8000 2,000,000 8,400,000 RAPHEX Answer to 2003 General Question G80 E. 1 byte = 8 bits, 1 Mbyte = 1024 x 1024 = 1,044,448,575 bytes = 8,388,608 bits. RAPHEX General Question 2003 G81: For protection purposes, the absorbed dose is multiplied by a “radiation weighing factor” wR is ______. A. B. C. D. E. 1 5 10 20 50 RAPHEX Answer to 2003 General Question G81 D. See NCRP Report 116.