Magnetic resonance imaging of the breast, accepted by the FDA for use as a supplemental tool to mammography in 1991, provides exquisitely detailed information about very small lesions that mammography and ultrasound often cannot detect. Of the 5,000 MRI scanners in the United States, close to a quarter are being used for breast exams.
While MRI in no way is usurping mammography’s dominance in breast cancer screening, it is shining as an adjunct for a variety of types of high-risk patients who fit specific criteria. The importance of highly experienced MRI breast specialists to perform these examinations cannot be overemphasized.
The High Risk Pool
Elizabeth Morris, M.D., assistant radiologist, at Memorial Sloan Kettering Cancer Center (New York, N.Y.) describes her study that determined the usefulness of breast MRI for very select patient populations such as women who are at increased risk for developing cancer, including those with a strong family history or with a known biopsy result that revealed a malignancy. Another indication would be a woman who has completed a breast conserving “lumpectomy” yet still has positive margins. Pre-surgical planning with MRI informs the surgeon as to the specific size and location of the tumor he or she is attempting to excise.
Young women with dense breasts who have cancers that are difficult to detect mammographically or those with a great amount of DCIS (ductal carcinoma in situ) associated with them comprise another class of high-risk patients for which breast MRI makes good sense.
In a study using a GE Medical Systems (Waukesha, Wis.) 1.5 Tesla Horizon scanner with breast coils and contrast injection, Morris’ group discovered several very small cancers that were not detected with mammography. “The screening trial found that we were able to detect cancers with MR that weren’t detected by other means in these patients,” Morris says. “It happened in 4 percent of the patients, which is very high for a screening study. It went up to 8 percent if they had a personal and family history of breast cancer. We were surprised at how high that was.” With mammography, the detection rate is usually about 0.6 percent, according to Morris.
Bruce A. Porter, M.D., F.A.C.R., medical director of First Hill Diagnostic Imaging and clinical associate professor at the University of Washington (Seattle) explains their group uses breast MRI solely for high-risk patients because it provides imaging data not available through other techniques.
“Especially using dynamic information, we commonly find and confirm tumors that are between three and five millimeters in diameter,” explains Porter. “Almost by definition, these would be women whose mammograms would be negative.”
Besides the high-risk categories of patients mentioned by Morris, Porter cites other women who benefit from breast MRI. A small number of breast cancers present with positive malignant axillary nodes, but normal breast exams and mammograms. MR is capable of locating the primary site. Women who have had breast implant surgery improve their care from information obtained through MR studies, too. In approximately 10 percent of women who have biopsy-diagnosed tumors in one breast, they will have another tumor in the contralateral breast or for women with invasive lobular carcinoma, there is frequently a circumstance of multifocal disease in the first breast that includes tumors undetected by mammography or ultrasound.
|Fifty-five-year-old woman with a prior LT cancer and new malignancy in the RT breast with mixed ductal/lobular features on biopsy. MR was used to determine the extent of the tumor and assess the left breast for recurrance.|
|Clinical image of a fifty-seven-year-old woman with malignant right axillary adenopathy. A 1.3-cm mass was detected by MR in the right breast. Both images on this page courtesy of First Hill Diagnostic Imaging.|
“When MR is done by an experienced group, it has a very high negative predictive value,” says Porter. “It’s one of the best tests we have in modern medicine to say there is nothing lurking on the other side.”
Richard Reitherman, M.D., Ph.D., director of women’s imaging at the Newport Diagnostic Center (Newport Beach, Calif.) concurs. “The people who do breast MRI should be breast radiologists as opposed to MR specialists,” says Reitherman.
Because breast imaging and treatment is a very integrated field, the radiologists who perform mammographic and ultrasound studies, are in close contact with surgeons, pathologists and treating physicians. And thus, Reitherman believes the best way to increase the value of new applications in breast MRI involves having a subspecialist perform the scans so they become integrated into a multimodality, multispecialty application for breast cancer diagnosis and treatment.
Paul D. Friedman, D.O., attending radiologist and breast interventionalist at St. Barnabas Medical Center in Livingston, N.J., agrees with this multidisciplinary approach. They are using their Philips Medical Systems (Bothell, Wash.) Intera 1.5 Tesla scanner to image high-risk patients for diagnostic purposes and for needle localization for biopsy of suspicious lesions.
“We correlate all of the mammographic films, ultrasound and any outside films and then we do the MRI,” Friedman says. They have dedicated breast specialists and mammographers reading the films.
Their scanner is equipped with new SENSE technology developed by Philips designed to image more quickly with thinner slices to improve resolution. Friedman says that allows them to image both breasts simultaneously, with a typical study taking 25 minutes to complete.
SENSE (SENSitivity Encoding) is a technique based on the use of multiple RF coils and receivers. Improvements in acquisition speed — greater than that possible through conventional methods involving increased gradient strength — is intended to improve efficiency for this real-time imaging modality.
There have been two issues of paramount importance in providing appropriate MR studies for patients with breast cancer. The first is the need to use a system that is capable of acquiring both breasts simultaneously. The second is to provide images in the sagittal plane because mammographers are accustomed to reviewing images and seeing breast structures in this way.
GEMS addresses these issues through an application called EXCITE, which has just been applied to their breast imaging system. Prior to the launch of this new capability, radiologists scanned one breast at a time, with an overnight interim period to allow contrast material to be metabolized out of the patient’s body. Huge amounts of data may be acquired in one of these studies, up to hundreds of images in a sequence or an exam, which presents workflow and image reconstruction issues.
Confirma’s new CADstream produces a 3D volume rendering
of a pre-contrast image with tumors highlighted.
Mona Theobald, GEMS general manager Americas MR sales and marketing says, “This is new technology and a new data pipeline in the MR scanner that allows this system to scan data much more rapidly at high resolution.” The system is capable of reconstructing 400 images per second, enabling bilateral breast imaging in the sagittal plane with contrast injections and high spatial resolution imaging. Any installed GEMS MR scanner can be upgraded to include EXCITE technology, and Theobald says the breast application runs the most efficiently using this enhancement.
Another question that often arises is the optimum level of field strength of the magnet to use in breast MRI.
Porter says they have found their Siemens Harmony 1.0 Tesla MR scanner with dedicated breast coils provides images with few artifacts and reliable high-resolution images to deliver the clinical information they require.
“At higher field strengths, motion sensitivity becomes greater, chemical shift becomes greater, and inhomogeneity of the radiofrequency field becomes more of an issue,” explains Porter who describes that imaging the breast is like driving on ice — it requires more finesse than raw power. He believes that gradient amplifiers are a more critical component. In his courses to teach clinicians MR breast imaging techniques, he finds that those with a higher field strength magnet may face challenges he does not.
Helmuth Schultze-Haakh, MR collaborations manager of the Pacific Region for Siemens Medical Solutions (Malvern, Pa.), explains that over the past decade, two approaches to breast MR were developed. The first, pioneered by radiologists in Germany, employs injection of a bolus of gadolinium to quantify and display uptake and washout of the contrast through the vasculature of the tumor. The second technique, developed in the U.S., takes advantage of an image software enhancement called Rotating Delivery of Excitation Off-resonance (RODEO) to improve the resolution of morphologic features of the tumor being studied.
Porter explains that his group employs a hybrid approach that incorporates both techniques for breast imaging to produce high-resolution morphologic imaging with dynamic kinetic information from contrast studies.
By combining both techniques, clinicians increase the specificity required for making treatment decisions. Porter describes that when they image women with a known tumor in one breast, between 3 and 10 percent will have a tumor in the contralateral breast that is undetected on mammography. This information has a high impact on the management of that patient.
Typically, a pre-contrast image acquisition is followed by an intravenous injection and then five one-minute acquisitions. Comparing data between all of the single acquisitions produces a dynamic curve evaluation to identify the way a particular lesion enhances over all the time points. Reitherman, who uses a Siemens Symphony 1.5 Tesla scanner with breast coils, describes the characteristics of many malignancies including those of the breast. Tumor angiogenesis occurs in all organs of the body, and involves the formation of abnormal blood vessels used to nourish the tumor. The features of this vasculature allow one aspect of specificity in diagnosis.
“Tumor angiogenic vessels have two basic abnormalities that we monitor,” says Reitherman. “The vessels are more permeable and the gadolinium leaks out more quickly, and the vessels characteristically form arterial-venous malformations which makes the blood wash out more quickly.”
The classic malignant curve during an MR study would show a high initial uptake within the first 60 to 90 seconds, and then a “wash out” where the curve reverses itself and the clinician sees a drop in the absolute intensity within the tumor volume.
The second type of curve is one that enhances rapidly, but after the initial 60 to 90 seconds, it plateaus. The third kind of dynamic curve is one where after the initial phase, it continues to increase over time.
However, many cancers do not exhibit the high washout curve, according to Reitherman. So they couple the findings from the dynamic study with high-resolution images that reveal the morphology of the tumor mass, and define whether the outer edges are smooth or fuzzy. Reitherman is using a new software tool scheduled for release this month, for interpreting these dynamic curves. A product of Confirma Inc. (Kirkland, Wash.), CADstream performs processing functions that physicians currently are accomplishing through manual calculations.
Mary Gatewood, product manager for CADstream, describes this approach as an efficiency tool for breast MRI.
“It does things like subtraction, multiplanar formats, … within about a 15-minute processing time,” explains Gatewood. Other than the autoprocessing capability, other features assist the physician in interpreting images. One segment of this application is designed to register images to compensate for any patient movement during the study. Because these studies involve the acquisition of a series of images, even breathing could decrease the specificity of interpretation. The image registration feature provides a summary of whether or not major correction was required, aler ting the reader to that fact.
The product provides an interactive tool, where the physician can run the computer mouse over an image and see the curve for any point on that image. Currently, physicians ask their technicians to find an area where they want to see the curve, and perform manual calculations for the information.
“One of the most popular features about the product is the angiogenesis map which is a color overlay that corresponds to contrast uptake and washout,” says Gatewood. Employing three different colors to denote the variations in uptake and washout over a specified period of time, the physician gains valuable information about unique tumor qualities.
Reitherman describes that for a new user, someone who has not been doing breast MRIs for a long time, that CADstream offers straightforward methods of analyzing images that simplify the process.
Tissue Sampling: A Vital Function
Because MRI is capable of identifying lesions that are undetected with other imaging techniques, being able to use MR guidance for needle locations and tissue sampling is critical to the effective and efficient use of this modality in managing patients with breast cancer.
“We’ve done more than 50 MRI needle localizations on lesions that were occult to mammography and ultrasonography,” says Friedman. These were lesions that would have been missed without MRI, and about 30 percent of the women had either cancer or a high-risk lesion. They had MRI exams because they fit into high-risk categories of patients such as those with a family history or other factor, but their cancer would have been missed until it had spread further if their care had been directed with just the usual imaging studies.
Xiaoming Chen, M.D., Ph.D. assistant professor in the department of radiology at the University of Washington, has been involved in a study where they used a standard 14-gauge stainless steel core biopsy needle to obtain tissue samples.
“This new method uses an MR-compatible coaxial device which consists of an outer titanium sheath and an inner titanium stylet to target the lesion,” says Chen. The titanium sheath is inserted into the breast tissue and imaged using their GEMS 1.5 Tesla scanner with dedicated breast coils. Once they are sure the sheath is in contact with the lesion, the patient is moved two meters away from the bore of the magnet where the sample is obtained. They do not have any problems with the stainless steel needle being attracted by the magnet at this distance.
At the University of Washington, they use MR prior to the first surgery to look for multifocal or contralateral disease because that helps to decide whether breast-conserving surgery is an option, or if a mastectomy would be the best way to proceed. They can use this technique to sample any lesions they suspect of being cancerous.
Suros Surgical Systems Inc. (Indianapolis, Ind.) launched a new product in May: the ATEC breast biopsy system that is designed to enable MR-guided biopsies within 30 minutes. This vacuum-assisted breast biopsy device is pneumatically powered (air driven) which means it is MRI compatible. Zeeshan Shah, M.D., associate professor of radiology at Indiana University School of Medicine relates that every patient who they have used this system to obtain tissue samples on has been amazed by how quick and how easy the biopsy was. Using the ATEC system, tissue samples can be acquired every 3.5 seconds, 10 times faster than with any other vacuum-assisted breast biopsy system.
Timothy Goedde, M.D., medical director of Suros Surgical, explains that since the system is air driven, and there are no electric cables in the room, they use a metal 12-gauge needle inside a plastic housing to obtain the sample. This provides large enough samples for analysis.
Despite the many advantages, there are a few drawbacks to the use of MRI for imaging the breast. Unlike mammography, this modality is unable to image calcifications that can indicate breast cancer. MRI is a more expensive imaging technique at nearly 10 times the cost of mammography. Some patients experience claustrophobia in these scanners, and MRI can produce a moderate number of false-positive findings which result in biopsies for benign lesions. However, experienced breast MRI practitioners believe the benefits far outweigh the drawbacks.
MRI of the breast has become the standard of practice in many women’s imaging centers to improve detection of very small lesions. The growth in the use of this modality increased 45 percent between 2001 and 2002. With advances in the scanners and their image processing software, and the development of new devices to enable faster and improved biopsy techniques, this modality likely will increase in popularity across the country in the management of patients with breast cancer.