DIANNE GUIANG 1204474
Exposures made at the same kVp and mA stations of the same phantom thickness should produce the same optical density on the resulting image. This is referred to as reproducibility (Papp, 2011, p. 107). This speaks to the fact that the radiation intensity produced by the x-ray tube should be the same given the same technique setting.
Instead of looking at the optical densities of images, an alternate method that can be performed to examine reproducibility is with the use of an exposure meter, also known as a dosimeter; this was the chosen method for the lab that was performed in x-ray room 4 in the B114 lab of the Institute of Applied Health Sciences building. The process involved making 10 separate exposures of the exposure meter at 100 cm SID with the technical factors set at 60 kVp and 5 mAs. In between each exposure, factor settings were changed to provide different combinations of 5 mAs; this can be seen in Table 1 below.
Instead of looking at the optical densities of images, an alternate method that can be performed to examine reproducibility is with the use of an exposure meter, also known as a dosimeter; this was the chosen method for the lab that was performed in x-ray room 4 in the B114 lab of the Institute of Applied Health Sciences building. The process involved making 10 separate exposures of the exposure meter at 100 cm SID with the technical factors set at 60 kVp and 5 mAs. In between each exposure, factor settings were changed to provide different combinations of 5 mAs; this can be seen in Table 1 below.
To able to establish whether the reproducibility for the x-ray unit in room 4 is within acceptable limits, the reproducibility coefficient of variation was first determined using the equation:
Calculation:
C = 1/0.0172 {[(0.017 - 0.0172)^2 * 8 + (0.018-0.0172)^2 *2]/(10-1)}^1/2
C = 0.02451
Mean value of exposure measurement compared to each exposure reading:
(0.017 - 0.172)/0.0172 = -1.16 %
(0.018 - 0.0172)/0.0172 = 4.65%
According to Safety Code 35 (S.C. 35), the coefficient of variation of any ten consecutive radiation irradiation measurements, should be no greater than 0.05, and each of the ten irradiation measurements should be within 15% of the mean value of the ten measurements. On the other hand, the Healing Arts Radiation Protection Act (H.A.R.P) states that the coefficient of variation of any ten consecutive radiation irradiation measurements, should be no greater than 0.08, and each of the ten irradiation measurements should be within 20% of the mean value of the ten measurements. Since the recorded values from the performed lab resulted in a coefficient variation of 0.02451, it can be concluded that the x-ray unit in room 4 is within acceptable limits. Also, as calculated above, each of the ten irradiation measurements are well within 15% and 20% of the mean value of the ten measurements; the x-ray unit also passes this criteria.
According to S.C. 35, the reproducibility test for an x-ray unit should be performed annually. It is important make sure that the reproducibility for an x-ray unit is within acceptable limits to ensure that the same results will be obtained when the same technical factors are selected. This way, if a technologist wishes to reproduce a good quality image, they can be confident that the same technique setting will produce the same result. This would then eliminate the need for a repeat x-ray which reduces patient dose.
C = 1/0.0172 {[(0.017 - 0.0172)^2 * 8 + (0.018-0.0172)^2 *2]/(10-1)}^1/2
C = 0.02451
Mean value of exposure measurement compared to each exposure reading:
(0.017 - 0.172)/0.0172 = -1.16 %
(0.018 - 0.0172)/0.0172 = 4.65%
According to Safety Code 35 (S.C. 35), the coefficient of variation of any ten consecutive radiation irradiation measurements, should be no greater than 0.05, and each of the ten irradiation measurements should be within 15% of the mean value of the ten measurements. On the other hand, the Healing Arts Radiation Protection Act (H.A.R.P) states that the coefficient of variation of any ten consecutive radiation irradiation measurements, should be no greater than 0.08, and each of the ten irradiation measurements should be within 20% of the mean value of the ten measurements. Since the recorded values from the performed lab resulted in a coefficient variation of 0.02451, it can be concluded that the x-ray unit in room 4 is within acceptable limits. Also, as calculated above, each of the ten irradiation measurements are well within 15% and 20% of the mean value of the ten measurements; the x-ray unit also passes this criteria.
According to S.C. 35, the reproducibility test for an x-ray unit should be performed annually. It is important make sure that the reproducibility for an x-ray unit is within acceptable limits to ensure that the same results will be obtained when the same technical factors are selected. This way, if a technologist wishes to reproduce a good quality image, they can be confident that the same technique setting will produce the same result. This would then eliminate the need for a repeat x-ray which reduces patient dose.
REFERENCES
Health Canada. (2008). Safety code 35: Safety procedures for the installation, use and
control of x-ray equipment in large medical radiological facilities.
Retrieved from http://www.hc-sc.gc.ca.
Service Ontario. (2011). Healing Arts Radiation Protection Act.
Retrieved from http://www.e-laws.gov.on.ca/html/regs/english/elaws_regs_900543_e.htm.
Papp, J. (2011). Quality Management in the Imaging Science
(4th ed.). St. Louis, MO: Elsevier Mosby.
Health Canada. (2008). Safety code 35: Safety procedures for the installation, use and
control of x-ray equipment in large medical radiological facilities.
Retrieved from http://www.hc-sc.gc.ca.
Service Ontario. (2011). Healing Arts Radiation Protection Act.
Retrieved from http://www.e-laws.gov.on.ca/html/regs/english/elaws_regs_900543_e.htm.
Papp, J. (2011). Quality Management in the Imaging Science
(4th ed.). St. Louis, MO: Elsevier Mosby.