"At the correct dose, there should be no injury,” said Dr. Cynthia McCollough, from at the Mayo Clinic (Rochester, MN, USA). "We believe in the clinical value of perfusion CT, so we're trying to lower the dose and reduce the stigma.” Dr. McCollough and her colleagues created a new image-processing algorithm that can give radiologists all of the information they need using as up to 20 times less radiation, depending on the diagnostic application. The research was presented July 20, 2010, at the 52nd annual meeting of the American Association of Physicists in Medicine (AAPM) in Philadelphia PA, USA.
A typical CT perfusion procedure lasts approximately half a minute and scans the same tissue many times, each scan at a low dose. These scans both reveal the internal anatomy of the patient and show how levels of a contrast agent, such as iodine injected into the bloodstream, change of over time. Changing concentrations of iodine can be used to calculate blood volume and flow in order to detect injuries to blood vessels or tumor responses to treatment.
The new adaptive algorithm compares these 20-30 scans and can distinguish between anatomic regions that do not change from moment to moment and those regions that carry the contrast agent--effectively reducing image noise while preserving iodine signal. The quality of each scan improves through nonlinear comparisons with scans acquired earlier and later in the exam.
"When we use very low doses, the noise gets so high that it's hard to tell what you are seeing,” said Dr. Juan Carlos Ramirez Giraldo. "With this algorithm, we're trying to maintain both the image quality, so that a doctor can recognize the anatomic structures, and the functional information, which is conveyed by analyzing the flow of the contrast agent over the many low dose scans.”
At the AAPM meeting, the researchers presented animal data showing the effectiveness of the technique. They have also started to process data from clinical brain perfusion CT exams in patients. "We're up to 15 or 20 cases that we've shown to the docs, and they're all giving us the thumbs up,” said Dr. McCollough.
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