When fifth-year Rice University (Houston, Texas) graduate student Guoping Chang began working with PET/CT imaging, he never expected to find out that "less is more" when it comes to helping physicians make an accurate cancer diagnoses.
But it as it turns out, that's the key to a technique employed by Chang and other researchers at Rice and the University of Texas M. D. Anderson Cancer Center (Houston) as they aim to make CT/PET imaging more efficient.
In a paper published last month in The Journal of Nuclear Medicine, a team led by Chang described an amplitude gating technique that they say gives physicians a clearer picture of how tumors are responding to treatment.
CT scanners capture a 3-D image of the inside of the body. PET (positron emission tomography) scanners look for a radioactive signature. Before a PET scan, a patient is injected with slightly radioactive molecules tagged to track and adhere to particular cancer cells. As the molecules gather at those cells and decay, they give off a signal that the PET scanner can read.
Together, the scanners give doctors a good idea of a tumor's location and whether it's malignant or benign, the researchers noted. Subsequent scans can show how it's responding to treatment.
CT scans take relatively quick snapshots while PET scanners need as long as three minutes to capture an image from a single section of the body. The problem is patients have to breathe during PET scans so the images don't always correlate well, Chang explained.
"Patients might have lesions located in organs that move due to respiratory motion," said Chang's technical adviser, Osama Mawlawi, an associate professor in the Department of Imaging Physics at M.D. Anderson and an adjunct lecturer in electrical and computer engineering at Rice. "When patients breathe, these lesions will be blurred."
According to Rice, 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. 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.
"Less is better than more," Chang told Medical Device Daily. "That is exactly what surprised me." He said the fact that his team was able to help improve the ability of CT/PET imaging simply by discarding some of the data was "amazing."
A patient may take 40 breaths during those three minutes. Combining 40 images from a specific point in the breathing cycle makes for a much sharper image because the tumor will be in pretty much the same spot.
Mawlawi said that 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, according to the paper. Chang said patients were not required to modify their breathing in any way.
Chang, who earned his bachelor's degree in space physics at Beijing University, expects to defend his dissertation based on his imaging work in March. He said he became interested in the project shortly after joining Rice's Department of Electrical and Computer Engineering, where Professor John Clark is his academic adviser.
"Being able to image with good resolution means you might be able to catch a small tumor very early," Clark said. "It's a good piece of work."
Mawlawi credited Behnaam Aazhang, the J.S. Abercrombie Professor in and chair of Electrical and Computer Engineering at Rice, for his help in supporting the collaborative work between Rice and M.D. Anderson. The research was supported in part by a grant from GE Healthcare.
Chang, Mawlawi and Clark co-authored the paper with Tingting Chang, a Rice graduate student, and Tinsu Pan, an associate professor in the Department of Imaging Physics at M.D. Anderson. Chang won a Young Investigator Award for his presentation on the topic during the 56th annual Society of Nuclear Medicine meeting in Toronto last June, Rice noted.
Chang said that for him the best part of this research is that it can really benefit patients. "Our objective here is to save patients' lives using our technique," he said.
Amanda Pedersen, 229-471-4212;