Dual-Headed CZT Gamma Camera Finds Small Breast Tumors

CHICAGO—A home-grown molecular breast imaging system using a dual-headed cadmium-zinc-telluride (CZT) gamma camera was highly sensitive in detecting breast tumors less than 10 mm in size in a preliminary study of 100 patients with confirmed breast cancer. The camera, which was created by mounting two opposing 20 X 20 cm CZT detectors on an upright gantry, was configured by radiologists at the Mayo Clinic, Rochester, Minnesota, headed by Stephen Phillips, MD. Dr. Phillips presented the results at the Radiological Society of North America 92nd Annual Meeting (abstract LL-BR4224-B07).

Tc-99m sestamibi studies (20 mCi per injection) were performed in 100 patients with suspected breast lesions with an estimated diameter of less than 2 cm on ultrasound or mammography. All patients were scheduled for biopsy. Patients were imaged seated. Using light pain-free compression, 10-minute craniocaudal and mediolateral oblique views were obtained of each breast. Of the 100 patients studied, 54 had confirmed breast cancer at surgery; 82 lesions were identified in these 54 patients. Of these 82 breast cancers, the CZT camera found 76, for an overall sensitivity rate of 93%. The camera detected 9 of 12 tumors that were less than 5 mm in size, for a sensitivity rate of 75%. For lesions that were between 6 and 10 mm, the camera detected 25 of 27 tumors, for a sensitivity rate of 93%.

Sensitivity for all tumors 10 mm or less in size was 88%. For tumors greater than 10 mm, 42 of 43 were detected for a sensitivity of 98%. The sensitivity rate for finding cancers below 10 mm in size achieved by the dual-headed camera was more than 100% higher than the rate shown in previous studies of a single-headed CZT camera, Dr. Philips said.

The difference may be due to the increased number of views available when a camera is fitted with two heads instead of one. No single-view camera has detected all types of lesions, because craniocaudal and mediolateral oblique views have been needed. The gain in sensitivity by the dual-headed camera may be due, in part, to the ability of capturing opposing views, he said.

The technique did not detect six tumors, and four of these were invasive ductal carcinoma. Three of these tumors were 2 to 3 mm in size and below the resolving power of the CZT camera system. Two lesions were not detected because of a positioning error.

Since the 1990s, radiologists have known that large-field-of-view CZT cameras could find large breast tumors (over 2 cm). "When we had an opportunity to use small cameras to look at the heart, we decided to try using them to detect small tumors in the breast, because as a breast imager, my job is to find the smallest cancers possible," Dr. Phillips said.

The dual-headed system used in this study was put together by Mayo Clinic bioengineers according to radiologists' specifications. It is the only one of its kind, at least in the United States, Dr. Phillips said. "The next step is working with the companies that produce the cameras to see if a commercially viable product is possible, after we continue to prove the science behind it," he added.

Large Study in Progress

Mayo Clinic radiologists are currently evaluating the effectiveness of the technique as an adjunct to conventional mammography. A study in progress will use the dual-headed CZT camera to evaluate 2,000 high-risk women who have dense breast tissue on mammography. "We are looking at this population because mammography is very good for imaging fatty breasts. But everybody is concerned about what we don't see in women with high glandular densities in the breasts. So that is where we are focusing our research efforts at this time," Dr. Phillips said.