PET/CT Weds Imaging Technologies

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PET/CT Weds Two Imaging Technologies to See Disease Better


PET/CT, notes radiologist Richard Wahl, reveals both anatomic detail and metabolic activity of tumors.

PET, or positron emission tomography, is very good at giving doctors pictures of functions and metabolic changes in the body, including the activity of tumors. Unfortunately, this imaging technology is not good at determining precisely where in the body such changes are taking place.

CT, or computed tomography, on the other hand, is an excellent tool for showing the exact size and anatomic location of a tumor. But unlike PET, it can’t reveal whether or not the mass is malignant, or whether it has spread to lymph nodes.

Given the advantages and disadvantages of each technology, considered the best imaging tests for cancer, why not wed the two? Johns Hopkins, the first U.S. hospital to install a combination PET/CT scanner for patients in a clinical setting, has done just that.

“Now we’re able to get hybrid images of both anatomic detail and metabolic activity, of both form and function,” says radiologist Richard Wahl. “The sum of the two, we believe, is greater than the individual parts.”

Indeed, in one study of 28 ovarian cancer patients, Hopkins radiologists have found that PET/CT detects cancer spread more accurately than PET alone. The radiologists found 3 true positive and 2 true negative results with PET alone, and 14 true positives and 10 true negatives with PET/CT. Also, PET/CT had a fairly high sensitivity rate, accurately diagnosing cancer 73.6 percent of the time.

“We know better where the tumor is, whether it’s localized or spread,” says Wahl.

Wahl and other radiologists are finding similar results in evaluating PET/CT images of colorectal and lung cancers. So promising are the findings that the scanner is being used to detect a variety of other diseases, including breast cancer and melanoma. In head and neck cancers, Wahl says, the technology is especially effective because of complicated anatomy and critical structures in the neck. PET/CT allows surgeons to see precisely where tiny lesions are located, and minimize dissection and disfigurement.

“The more complex and variable the anatomy, the greater the efficacy of PET/CT,” Wahl says.

He adds that the PET piece of the combined imaging scanner has been effective in determining whether cancer treatments, like chemotherapy and radiation therapy, are working. “Unfortunately, all cancer therapies don’t work,” Wahl explains. “PET/CT gives us very rapid feedback on the efficacy of therapy.”