August 27, 2015 — Radiologists at a Japanese hospital were baffled when dark spots began appearing on computed radiography (CR) images in March 2011. They discovered that the spots were caused by fallout from the nuclear disaster at the nearby Fukushima Daiichi nuclear power plant, according to an August 21 article in the American Journal of Roentgenology.
Researchers believe the spots represent radioisotopes from the Fukushima Daiichi accident that were suspended in the air as particulate matter. The radioisotopes filtered into CR imaging plates (IPs) to create artifacts on images. Even today, black spots are still appearing on some images, according to the team led by Yasuhiro Kashimura.
The artifacts have not impeded the diagnostic abilities of radiologists at the hospital, and the fallout itself does not represent any more of a health hazard than normal background radiation. But the issue has forced staff members at the hospital to change how they handle CR imaging plates to contain the contamination (AJR, August 21, 2015).
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“Therefore, any effects on humans of the radioactive material … that caused the black spots on CR images can be ignored,” the authors wrote. “That is, the health implications of the dose from individual contaminated cassettes are negligible, although the effects on human health from the radioactive fallout generally remain unclear.”How has the staff at Iwaki Kyoritsu General Hospital adapted to the situation? While radioactive material on the surface of a cassette or IP can be wiped off, isotopes adhering to the felt inside the cassette cannot be removed. Therefore, radiology personnel should erase latent images from an imaging plate immediately before clinical use, and read the IPs quickly after an x-ray exam.
As a side note, the researchers pointed out that this issue probably was not observed after other nuclear disasters such as Three Mile Island in 1979 and Chernobyl in 1986, as computed radiography was not in widespread use at the time.
While the problem has subsided somewhat since the disaster, personnel from Iwaki Kyoritsu are still dealing with fallout — both literal and metaphorical — four years later.
“Although fewer black spots were detected in radiographic images taken after April 2011, some were still observed more than six months later,” Kashimura and Chida wrote. “Furthermore, we still observe some black spots even today.”
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