Applied Radiology

Kathleen M. Dallessio

Although most imaging studies and biopsies of the breast are conducted using mammography or ultrasound, in some cases, magnetic resonance (MR) imaging may be the most appropriate modality.

"There are a number of indications for breast MRI," said Steven E. Harms, MD, FACR, Professor of Radiology, University of Arkansas for Medical Sciences, Little Rock, AR in an interview with Applied Radiology . Dr. Harms is also the Medical Director at Aurora Imaging Technology, Inc. , North Andover, MA. "Probably the most common use is in a patient with an inconclusive clinical or diagnostic imaging study. Getting question marks on imaging exams is not unusual--approximately 10% of mammograms require some other kind of test--and breast MRI is the 'high court' of breast imaging. It's very similar to having an abnormal chest X-ray and being able to get a chest computed tomography (CT). Breast MRI is the back-up procedure for all other breast imaging procedures; it's at the top of the food chain."

Breast MRI can be especially helpful in women who have impaired mammography results due to dense breast tissue. It can also be used to detect occult primary breast cancer in patients presenting with metastatic disease without a known primary tumor. "Other indications," noted Harms, "include any patient with a high suspicion of cancer who is a breast-conservation candidate. You can determine the presence of additional disease. You can determine the extent of the disease for more appropriate therapy. In patients who have had a lumpectomy with positive margins, MR can evaluate for the presence of additional disease, which will help to determine whether to do a lumpectomy or a mastectomy."

MR can also be used to monitor cancer therapy. "We can evaluate adjuvant therapy or chemotherapy to determine if there is a response to chemotherapy or the extent of residual disease in the breast of patients who might be candidates for breast conservation after chemotherapy," said Harms.

This imaging modality is also very useful for women with silicone breast implants, since MR studies are not impaired by the presence of silicone injections or implants as are mammography and ultrasound. "In women with silicone implants," added Harms, "we can not only find the cancer but also determine if the implants are intact or if there is free silicone in the breast."

In addition to finding cancer, MR imaging can also be used to exclude the presence of breast cancer in women who are determined to be at high-risk due to family history, genetic markers, or high-risk histology. "For example," said Harms, "if a patient has a cancer on one side, the other side needs to be evaluated to make sure there's not a cancer on the other side. Even if all the other imaging studies are negative, MRI can pick up additional disease."

One major drawback, however, noted Harms, has been that once the lesion is found using MR imaging, the physician still had to rely on ultrasound for localization and biopsy. "One of the reasons we do breast MRI is that we can see tumors that you can't see any other way; they can't be seen with mammography or ultrasound. Obviously if MR reveals disease that can't be seen any other way, then you can't rely on those other methods to do the biopsy," he explained. "As part of providing a breast MRI service, we have to be able to perform biopsies and localization. We don't want to have an abnormal MRI suspicious for cancer and then have to tell the patient, 'We don't have any way of getting a tissue diagnosis.' That is a terrible position to be put in and that is the reason why I believe that breast intervention should be an integral part of providing breast MRI services."

To address this need, Aurora Imaging Technology has designed their Dedicated Breast Magnetic Resonance Imaging System with the newly approved Integrated Interventional System.

"Instead of building a machine to make breast images, with breast biopsy considered after the fact," said Harms, "our machine is built from the ground up with intervention in mind. What that means is that all of the imaging features of the machine--the magnetic field, the gradient, the patient table--are also designed for better intervention."

The imaging system, which has been on the market for several months, was recently upgraded to a gradient of 21 mT/m at 40 msec rise time. "This is fast enough to do dynamic scanning and yet still very linear," said Richard W. Rosene, vice president of sales at Aurora. The magnet is also being upgraded from 0.5 to 1.5 Tesla. The patient table acts as an incline plane. "All the coils are built up and around the breast," said Rosene.

Harms noted, "Our gradients are designed to be low-distortion gradients--the lowest distortion gradients in the business, with <1 mm of error over 44 cm, where the typical whole-body scan will have 2 to 4 cm of error. So it's a significant improvement in the linearity of the gradient. It is designed so that if you find an area of abnormality on the breast, you can accurately guide a needle into it and you won't be fighting distortion errors on the instrumentation."

The Interventional System (which was approved by the FDA in February for the localization, biopsy, and treatment of lesions visualized on MR images) is an extension to the patient table that attaches to the side. The extension, which can slide back and forth along the table, includes 2 mylar grids for each breast and a staging device that can be placed in any one of four quadrants. LED readout is used to locate lesions stereotactically to within 3 mm.

"The latest attachment, which is the interventional attachment, is simply the final piece that makes intervention possible with this machine. Instead of using regular compression plates as are used in mammography or even biopsy systems for mammography, these plates are designed to fix the skin of the breast so that there will be minimal movement in the breast tissue when you do the intervention," said Harms.

"One of the problems that add-on biopsy systems for whole-body MR systems have is that you don't have good access to the breast; you are usually working through a small hole, and not all the breast tissue can be biopsied," he continued. "The tissue near the chest wall is particularly difficult to biopsy with a whole-body system. Our system has a very open architecture because the whole table is designed for breast intervention. You've got lots of room to work, and you can approach the breast from the medial or the lateral side. Most add-on systems approach the breast only from the lateral side; ours can approach from the medial too."

"This is a relatively automated system," continued Harms. "With the workstation included, you put a cursor on the lesion and then mark the position where the lesion is and then mark the position of a fiducial marker on the stage that holds the needle. Then the scan console displays automatically calculated numbers that allow you to put the needle in place accurately."

"An additional highlight of the machine's interventional design is that the scan console is in the room so that the technologist who runs the scanner doesn't have to go outside the room to operate it," he said. "The scan console is right next to the interventional table, and you can see the images as you do the biopsy. You can run the scanner without ever having to leave the room."

One drawback to breast MR imaging is the lack of reimbursement for most examinations. "There are some new areas that are not yet readily reimbursed," said Harms. "The most visible one is high-risk patients, people who have a high genetic risk for breast cancer. Right now they do not have a suitable alternative: many of them are recommended to have prophylactic mastectomy. Another group that could benefit from breast MRI but are also not readily reimbursed is people with very dense breast tissue. They are not very well imaged by mammography and often undergo numerous additional tests because of the ambiguity of mammograms. Breast MRI has no problem imaging dense breasts and could be a suitable alternative. In fact, in Boston, Faulkner Hospital is conducting a study of women with dense breasts who could be scanned and pay out of pocket if they want to. So I think that the availability of a dedicated breast MRI that could do low-cost breast MRI procedures is a real benefit for those people because it offers them an alternative. But it's not readily reimbursed, so they have to pay out of pocket. Frankly, it's not likely to be very successful until we can get third-party reimbursement."

"The biggest difference in this device compared with what's out there is that the whole system is built from the ground up around intervention," concluded Harms. "It's not an afterthought add-on piece. As a result, this design will translate into clinical benefits of being able to do the biopsy faster, more easily, and more accurately."

Other breast MRI news

Suros Surgical Systems (Indianapolis, IN) recently previewed a new MRI-compatible version of its Automated Tissue Excision and Collection (ATEC) breast biopsy and excision system. The vacuum-assisted system can now be used with ultrasound, stereotactic systems, and MRI. It is capable of performing 16 biopsies per minute with either a 9- or 12-gauge disposable needle. The company has planned a full launch of the new system for the end of the first quarter of 2003.

MRI Devices (Wauskesha, WI) recently introduced a new open breast array coil for use on the Intera 1.5 MRI scanner from P hilips Medical Systems (Andover, MA). The coil has a four-channel design to image in either a unilateral or bilateral mode and an open design for ease of patient positioning and for use in biopsy or needle localization.