Annick Van den Abbeele, M.D. (left), and Chief Technologist Rick Tetrault, C.N.M.T., consult about a patient's PET scan.
Laboratory proven
As with many instruments that are now a familiar part of the clinical landscape, PET scanners were invented as research tools. It is only in the past few years that their diagnostic potential has been tapped by physicians — and reimbursed by insurers.
For all its technological virtuosity, the machine works by a rather simple principle. All cells absorb glucose — a common type of sugar — as fuel, but cancer cells are glucose guzzlers, absorbing the substance at much higher rates than normal cells. PET technology takes advantage of this fact by applying a radioactive "tag" to glucose that is then given to patients intravenously (through a vein). When tumor cells absorb the radioactively labeled glucose, they begin emitting positively charged electrons called positrons. The positrons collide with nearby electrons, producing gamma rays. As a patient is passed through the scanner, thousands of sensors in the machine's "doughnut" hole record the gamma-ray patterns. A computer then unscrambles the signals and reassembles them into actual images, providing a three-dimensional portrait of tumors' locations within the body. (Patients need to lie still during the scan because the quality of the image can be affected by motion.)
"[At the Institute,] we're commited to providing patients with the latest in diagnostic technology."
— Annick Van den Abbeele, M.D.
The technology's capabilities don't end there. Because active tumors absorb more radioactive glucose — and emit more positrons — than normal cells, the PET scanner can determine not merely where a particular tumor is, but also how much of it consists of living tissue, and how much of dead scar tissue — a capability beyond that of either MRI or CT scanners. Before the advent of PET scanners, the only way to determine the proportion of living and dead tissue in a tumor was to surgically remove a sample and examine it under a microscope. "Another advantage of PET technology is that it is possible to take an image of a patient's entire body to find signs of cancer spread, something that is impractical with current CT or MRI scanners," says Rick Tetrault, C.N.M.T., chief technologist in Nuclear Medicine.
A technology commitment
Since they represent a relatively new technology, PET scanners have been approved by Medicare for only five types of malignancies thus far: solitary masses in the lung, gastrointestinal cancers, melanomas, Hodgkin's and non-Hodgkin's lymphomas, and for determining the severity of non-small-cell lung cancers. As more data is collected, the number of approved applications is expected to grow, Van den Abbeele says. Many private insurers have already approved other applications.
"The purchase of this machine demonstrates the Institute's commitment to providing patients with the latest in diagnostic technology," Van den Abbeele says. "The Institute's leaders are to be commended for their work in making this possible."
The machine's high level of sensitivity means it is capable of detecting minute amounts of disease. "The scanner can detect tumors that are just four to five millimeters in diameter, compared to more than one centimeter with other technologies. That's roughly half the size we've been able to detect before," says Tetrault.
Because it can show how active tumors are as well as how widely they're dispersed, the PET scanner helps physicians determine which patients are most likely to benefit from surgery and which are not. Physicians will also be able to tell more quickly whether a particular therapy is effective, or whether another needs to be tried.
- Next: For distinguishing between disease types, the key is in the genes
- Page: 1 | 2 | 3 | 4 | 5
