Filters allow CT radiation dose to be cut without significant loss of acuity
CHICAGO (Reuters Health), Dec 9 - The dose of radiation delivered on computed tomography (CT) can be cut by as much as 75% in adults who require a chest CT, a team at Massachusetts General Hospital in Boston reported at the annual meeting of the Radiological Society of North America (RSNA).
A double-blind study of 35 chest CT images acquired at standard radiation dose (144-224 mAs) and at half-dose radiation (72-112 mAs) was conducted by Dr. Mannudeep Kalra and colleagues. Low-dose images were processed through 2D filters at two settings to reduce noise and increase sharpness.
Standard, original and filtered images were reviewed by two radiologists who were blinded as to which image was which. The readers rated the images on a five-point scale (1 was excellent and 5 was poor) for image noise, contrast and visibility of small structures.
Standard-dose images with subtle lesions were processed through the same 2D filters and read by the radiologists, who assessed them for noise and contrast, as well as number of lesions, lesion size, how conspicuous the lesions were and likely diagnosis.
“A significant improvement in both subjective and quantitative image noise with the 2D filters was noted without any decrease in contrast and visibility of small structures,” Dr. Kalra told Reuters Health.
“CT is the largest source of radiation for the general population,” he noted.
“With certain body lesions, such as in the chest, noise doesn’t affect the image so much,” Dr. Kalra said. “With lesions of the abdomen and head, image is more affected by noise.”
“You have to consider what lesion you want to look at,” Dr. Kalra said. “Gallstones are dense, liver tumors are soft. That will affect how much (filtering) you can use. With gallstones or kidney stones, you can use more filtering, so that you can reduce radiation dose by as much as 75%.”
“You also have to consider the size of the patient. With a child, you are starting with a low radiation dose, and so there is a limit as to how much lower you can go,” Dr. Kalra commented.
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