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Ruido-quitar técnica corta la dosis de la radiación por la mitad para los colonoscopies virtuales

por Brendon Nafziger, DOTmed News Associate Editor | June 22, 2010
Reducing image noise
is a technique to reduce
radiation exposure
A noise-removing technology can cut radiation dosage in half for virtual colonoscopies without significantly hurting the image quality, according to a new study.

The scans, called CT colonographies, performed with a technique known as adaptive statistical iterative reconstruction, or ASIR, delivered around 50 percent less radiation than a normal procedure without really affecting the clinical usefulness of the image, according to a study published Monday in the July issue of American Journal of Roentgenology.

"In patients, no significant image quality differences were identified between standard- and low-dose images using ASIR," C. Daniel Johnson, a professor of radiology at the Mayo Clinic in Scottsdale, Ariz. and lead author of the report, said in a statement.

ASIR reconstructs CT images using noise-canceling algorithms, allowing clearer images at lower doses, the authors said.

"It's basically a mathematical formula," Dr. Amy K. Hara, associate professor of radiology at the Mayo Clinic in Scottsdale, and co-author of the study, told DOTmed News.

"It looks at the neighbors next to each pixel...to figure out if the noise in that pixel is accurate or not. In real organs, there should be subtle changes in noise, not big differences between neighbors. So when there are big differences, [ASIR] eliminates that mathematically."

For the study, begun around two years ago, the researchers used a GE Healthcare-made scanner, the Discovery CT750 HD, with ASIR software built-in.

To create the images, the researchers mixed ASIR with normal filtered back projection reconstructions, setting the amount of the image reconstructed with ASIR to only around 40 percent.

This is because the researchers were "using an earlier version of ASIR, where if you turn it up to 100 percent, you have this noiseless image that has an artificial appearance to a lot of radiologists," Hara said.

For the study, the researchers first tested CT scans with ASIR on phantoms, or dose-calculating dummies, to get the settings right, then they performed the exams on 18 patients at the Mayo Clinic in Scarsdale.

As dictated by the screening protocol, each patient got scanned twice, once lying on the back, and once face down. First, a standard CT colonography technique was done on those in the supine position, delivering a radiation dose of around 5 mSv. Then, while prone, the patients got a scan with ASIR, delivering only half the dose, or about 2.5 mSv.

Three radiologists then graded the 2D and 3D images produced by the scans on a five-point scale, with four being nearly perfect, and zero diagnostically worthless.