Gamma camera detects small breast tumours
19 December 2006
San Antonio, Texas. A new technique, called molecular
breast imaging, can detect tumours less than 10mm in diameter. The imaging
unit uses a dual-head gamma camera system and resembles a mammography unit.
The technique, which is still under development, will likely be only
slightly more expensive to use than mammography, and will be much more
comfortable for women because much less pressure is needed to image a
breast. It will also be a lot cheaper than magnetic resonance imaging, which
is currently the best technology available.
Researchers at Mayo Clinic,
who helped develop the technology along with industry collaborators Gamma
Medica and GE Healthcare, say it may make it a valuable complementary
imaging technique to mammography,
This new technique is sensitive enough
to detect tumours less than 10mm (about 0.4 inches) in diameter in 88% of
cases where it is used. Early findings from an ongoing comparison of the
device with mammography show that it can detect small cancers that were not
found with mammography, say the investigators. Mayo Clinic physicist Michael
O’Connor, Ph.D., presented these results on Dec. 16, at the 2006 meeting of
the San Antonio Breast Cancer Symposium.
"Our ultimate goal is to detect
small cancers that may be inconspicuous or invisible on a mammogram for
high-risk women with dense breasts," says Dr. O’Connor.
"We hope that our
studies will eventually show our device to be almost as sensitive as
magnetic resonance imaging (MRI), which is probably the best diagnostic test
available to date, but is not widely used because of its expense," says
Stephen Phillips, M.D., a Mayo radiologist and a study co-author. An MRI
scan costs as much as ten times more than a traditional mammogram and
involves injection of a contrast agent.
Mammography uses low-dose X-rays
(ionizing radiation) to create images of the anatomy of breast tissue. If
the breasts are very dense, it can only accurately help in tumour diagnosis
in 30 to 50% of cases, says Deborah Rhodes, M.D., another study co-author.
Yet women who have dense breasts are four to six times more likely to
develop breast cancer, and more functioning breast tissue is available in
which disease can occur, she says.
Conventional gamma cameras cannot be
easily adapted for breast imaging. Instead, the investigators used new,
small semiconductor-based gamma cameras and incorporated them into a new
breast imaging system. Images obtained with these gamma cameras are not
affected by dense or fatty tissue.
In the procedure, women are injected with a small amount of the
radioactive drug sestamibi that preferentially travels to tumours, which
absorb the substance. These women then are seated in front of the device,
which looks like "a strange mammography unit," Dr. O’Connor says. Each
breast is lightly compressed between the gamma cameras with just enough
pressure to keep it from moving for 5 to 10 minutes while several images are
taken. "It is much more comfortable for women, because a force of only 15
pounds is used, compared to the 45-pound force compression needed to take a
mammogram," he says.
The image usually shows low, but some, absorption of
the sestamibi throughout the breast. In areas of cancer, the amount of drug
absorption is significantly increased by the cancer. Although some benign
conditions such as fibroadenomas will occasionally absorb the drug, creating
a false-positive result, the researchers believe that the error rate is less
than the approximately 10% rate found with traditional mammography.
research team used this innovative dual-head gamma camera system to scan 100
patients who had suspicious breast lesions that were small, with a diameter
of 2cm (four-fifths of an inch) or less. Eighty-two cancers were later
identified at surgery in 54 patients. The gamma camera detected 76 of the
cancers, giving it a 93% success rate in these cases. Some were missed,
either because the breast was not properly positioned in the device or
because they were too small to detect with this technology (2 to 4mm or
about 0.1 to 0.15 inches), says Dr. O’Connor. Still, the gamma camera was
88% accurate in picking up cancers less than 10mm.
"Although these initial
results are very exciting, we clearly need to image more patients to confirm
the promise of the device," says Dr. Rhodes. She says the team hopes to
complete the ongoing trial in the next two years.