Graduate Thesis Or Dissertation
 

Validation of radiographic automatic exposure control device testing in the era of filmless radiography : and new variables associated with testing

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2b88qg58m

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  • The exposure needed for a clinically useful image requires much less precision when using digital radiography (DR) than when using screen/film (SF) radiography. The Automatic Exposure Control (AEC) device was developed for ensuring accurate and precise exposures with SF technology. This thesis evaluates the importance of the AEC device in DR. Several tests were performed to evaluate the operation of the AEC devices. A performance test was used to measure variation associated with different tube potentials and phantom thicknesses. The criteria used for the performance test was dependent on the imaging device manufacturer. A balance test measured variation among detectors within the AEC device. The criteria used for the balance test was dependent on the imaging device manufacturer. A reproducibility test measured variation among exposure values when no changes were made to the testing materials. The reproducibility test was considered acceptable if the coefficient of variation was found to be less than or equal to 5%. A density test was used to measure the amount of user-selectable adjustment to the exposure. Tolerance for this adjustment was a 20 to 50% change in the exposure per step. The appropriateness of the exposure was examined using an Exposure Index (EI) range test. The criteria used for the EI range test was dependent on the imaging device manufacturer. Finally, the overall operation of each AEC device was examined. An AEC was determined to be functioning properly if it passed all above stated tests. Roughly a quarter of devices failed the performance test. One-third of the AEC devices failed the balance test. No AEC device failed the reproducibility test. Roughly 60% of the AEC devices failed the density test. Approximately 60% of the AEC devices failed the EI range test. Overall, nearly 80% of all AEC devices tested failed one or more test. There was no significant difference in the table AEC devices versus the upright AEC devices. More than three-fourths of AEC devices used with Cassette Radiography (CR) failed at least one test. All Direct Digital Radiography (DDR) systems failed at least one AEC test. Although the importance of AEC devices has shifted from ensuring good image quality to maintaining appropriate patient exposures, the research performed in this thesis confirms AEC device calibration is still important for patient care. This paper also demonstrates the need for updated AEC testing methods developed for use with CR and DDR.
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