Scintimammography researcher explores breast biopsy applications

Technique may be able to locate occult lesions

A nuclear medicine physician who has spearheaded the use of gamma cameras for breast imaging plans to discuss his latest research in a presentation at next month's Society of Nuclear Medicine meeting. Dr. Iraj Khalkhali of Harbor-UCLA Medical Center in Torrance, CA, believes that scintimammography could be useful for breast biopsy procedures, such as finding occult lesions that can't be located using anatomical-based imaging modalities like mammography.

Khalkhali was one of the first nuclear medicine physicians to begin working with Du Pont Merck's Cardiolite technetium sestamibi agent for detecting breast lesions. Khalkhali and others have found that the radiopharmaceutical can help differentiate malignant from benign breast lesions (SCAN 8/2/95). Du Pont, of North Billerica, MA, has sponsored a multicenter clinical trial to prove the utility of its agent for this application.

Scintimammography advocates believe that the technique will be more useful for biopsy applications than for screening. To this end, Khalkhali and others at Harbor have developed a device that can be used to localize lesions for biopsy.

The device retrofits to a standard gamma camera. The researchers at Harbor-UCLA have been using a gamma camera manufactured by Sopha Medical, now part of SMV America of Twinsburg, OH, and a specialized biopsy needle and guidewire device made by North American Scientific of North Hollywood, CA.

A patient with a suspicious lesion to be scanned with the technique lies prone on the gamma camera, with her breast hanging through a hole in the system's table. Below the hole are two plexiglass compression paddles that are fenestrated, or pierced with holes, through which a biopsy needle can be inserted.

The patient receives 30 mCi of sestamibi intravenously, and any areas of abnormal uptake are visualized in the persistence mode of the scan, according to Khalkhali. Three wires with cobalt-57 markers are overlaid over the region of interest as reference lines to provide x, y, and z axes. Cobalt-57 is used for localization because it has a different energy than technetium, Khalkhali said.

The reference lines help clinicians determine the holes in the compression paddle through which the biopsy needle and guidewire should be inserted. The biopsy needle is also tipped with cobalt-57, and when it reaches the region of interest the cobalt marker is removed and a dye is injected to help surgeons find the lesion. A standard guidewire is inserted to mark the lesion, the needle is removed, and the patient is sent to the operating room for surgical excision of the lesion.

The surgeon removes the tissue marked by the guidewire, and the excised specimen is sent back to nuclear medicine to confirm that the hot spot seen in the scintimammography image is in the specimen image, Khalkhali said.

Khalkhali's group published a paper on the technique in the European journal Nuclear Medicine Communication last year, and another paper will be published in the July issue of the Journal of Nuclear Medicine. Khalkhali will also discuss the work at a presentation he is giving on Wednesday morning at next week's SNM meeting in San Antonio.

In the Nuclear Medicine Communication article, the Harbor-UCLA researchers attempted localizations of 30 lesions in breast phantoms. The researchers successfully localized all 12 shallow lesions (20 to 39 mm deep), and 15 of 18 deep lesions (40 to 67 mm deep). All lesions larger than 1 cm were accurately identified, while all missed lesions were smaller than 1 cm in diameter. Of the missed lesions, all had a partially superimposed region of interest, indicating that the biopsy needle had come close to the lesion. This led the team to claim that 90% of all lesions were successfully localized.

Harbor-UCLA has received a patent for the technology and is interested in working with a nuclear medicine vendor to commercialize it, Khalkhali said. He believes that the technique would work best with a dedicated scintimammography gamma camera, which is probably years from becoming a commercial reality.

So far, the biggest difficulty has been recruiting patients for the studies, because scintimammography is not being used as a screening tool. Three patients were studied for the JNM article. All the patients Khalkhali has examined are women in whom metastatic lesions have been localized but the primary lesion can't be found, he said. The Harbor-UCLA researchers are accepting patients from across the U.S. who have axillary nodes that are positive for cancer yet who have occult primary lesions.

If the technique does achieve widespread use, Khalkhali believes it could help clinicians find lesions that aren't visible with anatomical imaging modalities.

"We believe that breast cancer starts as biological changes in the breast that we don't see with mammograms at the early stage," he said. "These women had normal mammograms, and on the three patients we sent to the JNM study, two of them had infiltrating ductal carcinoma."