SHELDON LIU, 1223168
Pixels are the foundation in producing a digital image. In the clinical setting, it is essential that the images being produced have good quality (spatial resolution), as well as accuracy. In computed radiography (CR) images, artifacts could arise from scratches, ghosting, film/screen contact, and mishandling of the cassette, which can pose a threat for diagnostic purposes. In contrast, any artifacts in digital radiography (DR) can be due to incorrect flat field corrections. Artifacts can easily hide or be mistaken for pathologies that do not exist. Consequently, these images will have to be repeated, resulting in excessive radiation to the patient due to poor quality control. Quality Assurance Procedure (QAP) is a software used in DR, designed to assess and correct distorted pixel to pixel variation within a certain degree. It uses a technique called flat fielding to compensate for a discrepancy in electronic gain, offset and variation in conversion layer thickness (Padgett & Kotre, 2004 ; Seibert, Boone, & Lindfors, 1998). The process is done by applying a uniform signal (averaging) to the pixels in order to produce a final uniform image.
Figure 4. Results from the QAP test.
Figure 4. Refers to the image quality test results conducted from QAP. On the left hand side are the lists of different tests performed and to the right are its corresponding parameters. Determining the status, whether the test has failed or passed, is achieved by the lower specification limit (LSL) and upper specification limit (USL). If the measurement falls out of the USL or LSL range, it will fail the test. For instance, the number of bad pixels was 122397. This well over exceeds the USL value of 30.
Flat Fielding QC should be tested for on a monthly basis to provide consistency in producing acceptable diagnostic images. The results have provided evidence that action is required in order to address the failed tests. The important part to the solution is determining the cause of the problem before deciding on immediately repairing or replacing equipment, which could cost a lot of money.
References
Padgett, R., & Kotre, C. J. (2004). Assessment of the effects of pixel loss on image quality in direct
digital radiography. Physics in medicine and biology,49(6), 977.
Seibert, J. A., Boone, J. M., & Lindfors, K. K. (1998). Flat-field correction technique for digital
detectors. In Medical Imaging'98 (pp. 348-354). International Society for Optics and Photonics.
digital radiography. Physics in medicine and biology,49(6), 977.
Seibert, J. A., Boone, J. M., & Lindfors, K. K. (1998). Flat-field correction technique for digital
detectors. In Medical Imaging'98 (pp. 348-354). International Society for Optics and Photonics.