The purpose of the linearity quality control lab was to test the linearity between mAs and dose. For part 1 of this experiment, a Radcheck was placed in the centre of the detector in room 6 at a distance of 75 cm from the x-ray tube. Multiple exposures were taken at 80 mA with small focal spot and 160 mA with large focal spot. At each mA station, 4 different mAs settings were used: 8, 16, 32 and 64, and each exposure at a different setting was taken twice. The kVp remained constant at 70 and the mR values on the Radcheck were recorded (refer to Table 1). During part 2, the same set up used as part 1 except this time the technical factor combinations were 8 mA at 0.2 s, 160 mA at 0.1 s, and 320 mA at 0.05 s and each exposure was taken twice at each combination of factors. Once again the kVp remained constant at 70 and the mR values on the Radcheck were recorded (refer to Table 2). This quality control test determines the accuracy of mA and time. When the mAs changes, their should be a proportional change in dose, therefore the ratio of mR/mAs should remain constant for each exposure. According to Papp (2011), in order for the x-ray unit to be within standards, the following equation must be true: lx1bar - x2barl ≤ 0.10(x1bar + x2bar). Part 1 Calculations: small focal spot: l0.01-0.00997l ≤ 0.10(0.01+0.00997) 0.00003 ≤ 0.001997 large focal spot: l0.01-0.0101l ≤ 0.10(0.01+0.0101) 0.001 ≤ 0.00201 Part 2 Calculations: l0.009906-0.00963l ≤ 0.10(0.009906+0.00963) 0.000276 ≤ 0.0019536 Based on the calculations above, the x-ray unit in room 6 is within standards. If the unit were to fall outside of the standard, a service technician would need to be brought in to fix it. Quality control tests should be preformed on the timer and kVp accuracy to determine if non-linearity could be as a result of other problems. The sticker on the Radcheck should also be looked at to verify it has recently been calibrated. Table 1 Table 2
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