PET scans effective in the detection of cancer

A new avenue of cancer detection was proven effective in two recent University studies. PET, or positron emission tomography, is coming to the forefront of medical imaging technology and can locate cancer and infections, researchers say.

Although the images produced by PET scans look similar to CAT, or computerized axial tomography, scans, a PET image shows tissue metabolism and biochemistry.

"PET is type of CAT scanner that makes pictures of the biochemistry of tissues," said assistant Internal Medicine Prof. Paul Shreve, one of the studies' authors. In comparison, both CAT scans and MRIs (magnetic resonance images) show anatomy, or "if there's a lump or a bump," Wahl said.

MALLORY S.E. FLOYD/Daily Dr. Richard Wahl, a professor of internal medicine and radiology at the University, stands next to a PET scanner. Machines like this one may be useful in future cancer detection.

"PET is substantially better than CAT to tell if (cancer) is spreading or not," said Internal Medicine and Radiology Prof. Richard Wahl, who co-authored of the studies. "The major clinical role is imaging cancer. ... To treat malignancy, you have go to know where the disease is located."

PET is especially useful in treating breast, lung and colorectal cancers, as well as lymphomas, melanomas and other types of cancer.

"One thing PET does very well is to tell if (the cancer) is localized or spread around," Wahl said.

Researchers have also "accumulated enough data to prove that PET scanning is useful in staging cancer," Shreve said.

Physicians stage cancer by estimating how far a malignancy has progressed. To make an accurate staging diagnosis, images must show where and how extensively a tumor has spread.

"Staging requires detecting small pieces of tumor," Shreve said. "The real power of PET is finding tumors we can't see on a CAT scan."

CAT scans work well when viewing large tumors, but smaller tumors may go unnoticed, Shreve said.

"PET scanners have a much greater ability to make good pictures," Shreve said. "When it comes to a really small tumor, that's when you need a good PET camera."

Some companies sell dual-head cameras, which are intended to be a less-expensive alternative to PET. But the images created by these cameras are "much less clear," Shreve said. "The practicing radiologists need to know this, and patients do too."

Many of the companies that manufacture and distribute the lower-line PET scans are "interested in profits, not the big picture," Shreve said.

Shreve said it is necessary to test new technology vigorously and said he wants to see an end to the push of "substandard medicine" on the public. "The whole thing is being driven by money issues," Shreve said. Hospital administrators decide which pieces of equipment to buy and from whom to buy them, Shreve said.

"The bottom line is that you need a good camera to take a good picture," Wahl said. "A good camera costs more money."

A PET scanner costs about $1 million, but "if you (scan) a lot of patients, it drives the cost down," Wahl said.

PET images are produced after patients are injected with radiotracers, which act like glucose. "Tumors use sugar like crazy and light up on the (PET) scan," Shreve said.

The radioactive tracers used with PET have become less expensive and more advanced in recent years. Their short half-life and low dose of radiation made them expensive in the past, Wahl said, but new technology has improved production and lowered cost.

"Knowing the correct diagnosis leads to appropriate therapy," Wahl said. In addition, diagnosing a patient correctly can eliminate extra tests and treatments to lower overall medical cost.

PET may also be helpful in quickly diagnosing infections. It is not unusual for a patient to arrive at the emergency room with a high fever and severe type of infection, Wahl said. PET has located infections within an hour in University studies, but Wahl said more studies must be done in this area before it can become a common diagnostic tool.

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