Since physicians can't ask patients to stop breathing for three minutes, Chang found a way to turn a patient's respiratory motion the amplitude into a waveform that serves as a kind of time code.
In the new method, patients are fitted with a flexible band around the chest that records their breathing cycles during the CT scan -- the three-dimensional X-ray taken as the patient slides through the ring-shaped device.
During the subsequent, much longer PET scan, the program creates a "gate," which allows data for specific points in the breathing cycle to pass through and throws away the rest. The program automatically correlates that data to the CT images.
A patient may take 40 breaths during those three minutes. Combining 40 images from a specific point in the breathing cycle say, mid-breath makes for a much sharper image because the tumor will be in pretty much the same spot.
Even better, Mawlawi said, the radiological signal captured by the "gated" PET scan is more coherent. "One of the important aspects of PET imaging is that it can tell us how malignant a lesion is," he said. "The scan gives us a specific number which is correlated with the measured signal intensity; the more accurate this number is, the better the physician's assessment is of a lesion's malignancy and response to treatment."
When someone undergoing therapy is scanned again, he said, "the change in signal intensity not just the size of the lesion tells us whether the patient is responding or not. This is equally important to the quality of the image."
In tests on 13 volunteer patients at M.D. Anderson, information gathered using the technique on 21 tumors was significantly better with Chang's gated technique than without, the paper shows. Patients were not required to modify their breathing in any way, Chang said; this enabled them to be as comfortable as possible duri
|Contact: David Ruth|