While the radiologists found, in general, the low-dose images to be subjectively slightly noisier, the differences were not clinically significant as they were always less than half a point on the scale, the authors said. That is, a 3-point image -- basically good with mildly unsharp edges -- was not significantly clinically different from one registering a 3.3 on the scale.

Still, the authors were somewhat surprised by the finding, as the image noise, when objectively measured, was around 24 percent lower on the ASIR-reconstructed scans.


The discrepancy between objective and subjective measures of noise on the images might come about as CT colonographies are such low-dose, noisy scans to begin with, the authors speculated: even routine doses for the scans are typically less than half of what's given in an ordinary CT abdominal scan.

"They're never really pretty images; they're always rather noisy," Hara suggested. "Little differences in really noisy images are harder to appreciate."

Predictably, as the size of the patient increased, as measured by the body mass index, image quality worsened.

"We know that in bigger patients you need more radiation dose. That will probably be the same for this as well," Hara said.

In future studies, the researchers suggested using more patients, and also cranking up newer iterations of the iterative reconstruction software to 100 percent.

In any case, the findings could help ease worries about virtual colonoscopies, which have become a subject of some controversy as pressure mounts on Medicare to reimburse the procedure. A bill introduced into Congress earlier this month would require Medicare to pay for it.




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