The Highs and Lows of Breast MR

Renee DiIulio

Breast MR has been lauded for its high sensitivity but condemned for its variable specificity. Some criticism is deserved, but some is left over from the use of earlier technology. Contrast agent improvements, surface coil technology advances, and new imaging protocols have helped to improve the exam over the past decade. Even so, no one thinks that breast MR should be a primary screening method for the general population?not just because of specificity issues but also because of the exam’s high cost. Still, as a screening tool for certain high-risk patients or a staging tool for cancer treatment, the technology is proving itself invaluable.

Why Screen?

“MR is safe and minimally invasive, requiring only the contrast injection,” says Sri Swaminathan, clinical scientist with Philips Medical Systems (Bothell, Wash).

Also, MR’s sensitivity is extremely high. According to study results, “The sensitivity of contrast-enhanced breast MR imaging for malignancy is close to 100%, an improvement over traditional methods of cancer detection.”¹ In other words, it can help detect cancers as well as determine exactly how wide they have spread.

Why Not Screen?

Unfortunately, the specificity of breast MR?which ranges from 37% to 97%?is not as high as its sensitivity.¹ However, according to Lawrence Ryner, PhD, research officer at the National Research Council (NRC) Institute for Biodiagnostics (Winnipeg, Manitoba), “Breast MR has evolved over the years. With early breast MR, even five years ago, specificity was below 50 percent. But over the years, with improvements in acquisition and analysis of data, it has improved to 80 percent.” Ryner suggests that if this statistic is compared to the specificity of mammography, which is around 80%, MR does not perform worse.

Lawrence Ryner, PhD, at the console of the 3T whole-body MRI scanner used for research at the NRC Institute for Biodiagnostics.

But the questions regarding the methodology’s specificity make some industry professionals uncomfortable. “MR will find a lot of bright spots, which, even if determined benign, create anxiety for the patient,” says Bruce A. Porter, MD, FACR, clinical radiologist at the Swedish Medical Center (Seattle).

Add to the list of negatives the high cost of the exam, and many agree that the methodology is not yet ready to be used as a primary screening method for the general population.

Who Should Be Referred?

For some patients, however, MR is recommended as a screening tool. Last year, the American College of Radiology (ACR of Reston, Va) published its first guidelines on indication for MR² that, not surprisingly, echo what experts told Medical Imaging. High-risk patients and mammography patients with uncertain findings typically should have MR exams. High-risk patients include those with a strong family history of breast cancer, those who carry the known breast cancer gene, and those who have a personal history of cancer. Other patients who benefit from MR screening include those with implants, scar tissue, or very dense breasts, which can interfere with mammography’s results.

But screening is only one area where MR brings benefits. “Breast MR is now recommended prior to any breast surgery to check the extent of the disease and look for other lumps,” Ryner says. “It’s useful to track a patient’s response to treatment during chemotherapy. It can distinguish whether a lump is scar tissue from a previous surgery or a recurrent tumor.”

How Can Specificity Be Improved?

This breast MRI (above) and a representative spectrum (below) demonstrate the elevated choline peak indicative of malignancy.

Of course, even in former cancer patients, if a lump is discovered, its nature will need to be determined. Clinicians and researchers constantly are looking for ways to improve the specificity of breast MR. Some improvements come with advances in hardware, and others with software; some are a combination of techniques to increase specificity.

Improvements in hardware have led to faster and better image acquisition. Ryner suggests that newer equipment, with higher magnetic fields, can further improve images and turnaround. “But you must buy new. Unfortunately, you can’t just upgrade your MR scanner magnet,” he says.

Ryner also advocates doing a full analysis of the data. “You don’t want to use an out-of-date technique, either in the acquisition or analysis,” he says. Faster techniques allow better analysis of the uptake of the contrast agent. “We are able to acquire several sets of images now as the agent goes through the breast for dynamic contrast-enhanced imaging,” he says, noting that this technique helps to improve the exam’s specificity.

CAD, another software tool, also enhances results. Porter uses CAD as a second reader and has found that it helps to improve specificity. “Depending on the time in a young woman’s menstrual cycle, you get all sorts of bright spots,” he says. “Many have a benign enhancement pattern, but if you have 20 exhibiting similar patterns and one with a rapid washout, CAD will pick out that area, drawing attention to something that might have been missed visually. It’s then possible to do an enhancement curve in real time.”

But the Swedish Medical Center doesn’t rely on CAD or MR alone. “In clinical practice, it’s rare to rely solely on MR. If the exam indicates that a tumor is likely to be malignant, we follow up with an ultrasound,” Porter explains.

A newer combination technique that would run concurrently with the MR exam is MR spectroscopy (MRS). This newer methodology measures choline levels within a selected area, producing a spectrum or line graph. Choline is thought to be associated with cancer cell replication and is often present in higher amounts in malignant tissue, according to Michael Garwood, PhD, associate director of the Center for Magnetic Resonance Research (CMRR of Chicago) and the Lillian Quist?Joyce Henline chair in biomedical research professor of radiology at the University of Minnesota Medical School (Minneapolis). “Early research has shown that using spectroscopy in conjunction with MR improves accuracy. Neither is perfect alone, but together, they work well,” he says.

CMRR’s Michael Garwood, PhD, says early research has shown that using spectroscopy in conjunction with MR improves accuracy.

Despite the positive results, Garwood believes that spectroscopy is not yet ready for widespread use, primarily because it’s not widely available. In fact, he notes that research findings will need to be replicated on both small and large scales before there is a big push from the medical community to obtain the technology from manufacturers. He explains that the software he uses was created and customized to run specifically on the CMRR’s equipment.

Porter is one physician who will need to see results before he endorses the new method. Citing additional cost and time, Porter believes that the results of spectroscopy will not preclude the need for biopsy. “I don’t know that it will have much real-world clinical utility,” he admits.

It’s too early to make that prediction, but Garwood expects the additional 10 minutes required to run MRS eventually can be reduced to 5 or 6 minutes. And a number of other early studies thus far have shown that spectroscopy can improve the specificity of MR. Still, it will likely not be enough to propel MR to the top of the list of screening options, according to Garwood?but it might help to reduce the need for additional follow-up tests, which will save cost and improve patient care.

References

1. Piccoli CW. The specificity of contrast-enhanced breast MR imaging. Magn Reson Imaging Clin N Am. 1994;2(4):557?71.
2. American College of Radiology (ACR). ACR practice guideline for the performance of magnetic resonance imaging (MRI) of the breast. ACR Practice Guideline. 2004 Oct:269?274.