The purpose of this lab is to check the efficiency of the computed radiography (CR) processor to see if it is functioning properly. Different components are utilized during the process of reading and erasing a cassette to ensure the residual image is erased. When a cassette is placed into the CR reader, mechanical features take the imaging plate out of the cassette. Following the removal of the plate, the latent (invisible) image is stimulated by a laser that scans the plate line by line in a raster pattern to knock off the electrons so they can be read. Afterwards a bright light will hit the imaging plate and release any electrons that were not released by the laser (Bushong, 2013).
To test the functioning of the CR processor, two exposures were taken on a CR plate. The first exposure was using the technical factors of 80 kilovolt peak (kVp) and 30 milliamperes second (mAs) with no filtration. The source to image distance (SID) was set to 150 cm with a collimated field of 10 cm X 10 cm with two pennies positioned at the centre of the CR plate. After the exposure was taken, the cassette was processed in the CR processor. The same cassette was used to take the second exposure. However, 80 kVp and the lowest possible mAs was used, as well as a 9 cm X 9 cm field centred on the same spot of the cassette but with no pennies. The cassette was processed in the CR processor, and the image was visually inspected for any remnant of the previous image. It was found that there was slight ghosting in the second image, therefore the CR system did not pass. The qualitative criteria for acceptance for the erasure thoroughness is absence of a ghost image of the lead block, or in our case pennies, from the first exposure to the re exposed image. The quantitative criteria for acceptance is EIGP<80, EIHR<380, PVGP<80, PVHR<80, PVSD<4. The main way to determine if the CR processor is working efficiently is to examine images to see if there is any ghosting. Ghosting is when remnants from the previous x-ray show up on the subsequent image (Papp, 2011). This could be due to a few factors. Firstly, if the bright light is burnt out or worn out because of age, residual electrons may be left behind causing them to show up on following x-rays. Secondly, ghosting may be present if the entire surface of the imaging plate is not exposed by the bright light because of misalignment. Last but not least, the mechanics may be out of sync reducing the length of time the imaging plate is held causing electrons to be left on the imaging plate. Ghost artifacts can be reduced in the clinical setting by erasing cassettes on a regular basis. Although a cassette may not be exposed to radiation, it is still receiving some exposure from the lighting in the room. Therefore erasing a cassette that has been sitting around can reduce the risk of ghosting. Regular quality control testing can also be done to ensure the equipment is functioning properly.
16 Comments
|