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WEDNESDAY, March 12, 2003 "Advances in Diagnosis and Management of Breast Cancer: MRI" Our guest for the evening is Nola Hylton, PhD., a radiologist at UCSF, specializing in magnetic resonance imaging research. Clearly, for detection and diagnosis, the standard of care is mammography, or x-ray of the breast. MRI is a technology that came along in the 1970s and images the body from head to toe in cross-sections. It is more complicated than x-ray and a lot less pleasant experience. The patient is required to remain still for about 40 minutes while moving through an enclosed tube. The detection of breast cancer was one of the early applications of MRI, asking the question of whether we can find breast cancer with it. At the time, the answer was “No”. The technology continued to develop. One of the important things that happened was the development of contrast agents, which, when injected into the patient, would light up the tumor on the image. This was the initial demonstration that MRI might be useful in diagnosing malignancies. Some important advantages include not using ionizing radiation and being 3-dimensional. Because the contrast makes the field light up like a light bulb, even very small tumors can be visualized. Because you are taking very small slices through the breast, MRI is not limited by breast density. Because you are not compressing the breasts, implants are not a problem. It has a high negative predictive value, meaning that if nothing is seen, there is nothing there. The disadvantages of the procedure are not insignificant. Most malignancies will enhance, but they are not the only things that enhance. The injection medium shows up brightly when it leaks out of vessels. Usually the vessels in the tumor leak first, so the earliest brightness is a signal of a leaky vascular bed that is often cancerous. The accuracy of actually determining what is cancer is very dependent on the skill of the radiologist. Another problem is that the scan time is long and requires the patient to remain motionless for up to an hour. It is also very costly, several thousand dollars versus one hundred dollars for a mammogram. There are also issues of size—both of the breast and the patient—as very large cannot fit in a closed tube. How does MRI compare to mammography? MRI is not meant to replace a mammogram, rather to augment it. Mammograms are easier to acquire, less expensive and have more reliable image quality. The question is “Where does MRI add value?” Here is a comparison:
Are injections put into the breast? No, the injections are just intravenous into the arm. The contrast agent is used in about 40 to 50% of all MRIs, so it is quite safe. Which works best for DCIS? In DCIS, the mammogram will show patterns of calcifications, generally a sign of breast disease. The MRI will shown none because they are too fine to show up, speckled enhancements that do show up are probably not cancer, more likely fat. Can both breasts be done at the same time? MRI can be configured to do one, or both breasts. To do both at the same time is a compromise, because you must look quickly at the contrast material before it diffuses into the breast tissue. Is it claustrophobic? The magnetic cylinder is six feet long and you must have the part of the body being scanned centered in the tube. Many people discover they are claustrophobic during this procedure. Noise is also a problem. It sometimes sounds like a jackhammer. Headsets for music help a little. Anesthesia should be avoided because it adds a great deal of time to the procedure. Is MRI safe? MRI is just controlled radio waves. The computer needs to block out radio waves in the environment, so it is not what gets out of the MRI, but not allowing ambient radio waves into the system that can destroy the picture. What is the difference between a PET and MRI? With PET (positron emission tomography) a substance emitting a positron is injected into the body. Cancer cells grow at a faster rate than normal tissue, so the PET scan will detect areas of greater uptake. MRI is not a photon-detecting device. It is fundamentally different. You would need a much greater amount of the injected element in order for it to be detected by MRI. PET is not that good for detecting breast cancer because it gives false positives. It doesn’t have good spatial resolution. It is used more for metastatic disease than for diagnosis of breast cancer because of its ability to scan the entire body. Are you continuing to do MRI studies in the axilla? There are two reasons why this type of study is problematic. Because the equipment is designed to scan the breast itself, the image quickly loses its quality as it moves into the axilla. The contrast material also goes quickly to the lymph nodes, so when a lymph node lights up, it is not necessarily cancerous. It will indicate an enlarged node or one with a different shape. How long should you wait to have an MRI after breast
reduction surgery? The recommendation is to wait at least six months so
that post-surgical changes and inflammation can go away. This may not be
practical if the issue is determining residual disease. The scan can be done as
long as it does not impact the biopsy cavity, but it isn’t the most reliable
use of MRI. Are there major differences in quality among MRI sites? Although anyone can purchase the coil needed to perform MRI, it is very dependent on the skill level of the radiologist reading the results for all of the reasons we have mentioned. What are the indications for MRI? An inconclusive mammogram A palpable abnormality with no mammographic findings Nipple discharge with no mammographic findings Recurrent breast cancer vs. scar tissue (scar tissue won’t enhance but cancer will) Again, technique is key, because a negative test might just mean it was below the detection level of the technician. With a detectable, suspicious mass, a FNA (fine needle aspiration) is better, although no test is free of false negatives. Whereas it is relatively easy to direct a needle localizer to something seen on mammogram, this is not true with MRI. The breast is not accessible at the time of the imaging and a needle cannot be used because of the magnet. All tools must be redesigned in order to do a biopsy with MRI. MRI is not a good screening test unless a person is at high risk or has highly dense breasts. In that case it may offer an alternative to bilateral prophylactic mastectomy. When is MRI used for staging? In Europe, where needle biopsies are not used commonly, MRI is used to rule out cancers diagnostically. In the U.S., the diagnostic workup prior to MRI is very comprehensive, so that most often patients already have a confirmed diagnosis of carcinoma. In these cases, MRI is most useful in staging the cancer for subsequent treatment decisions. Because it is 3-dimensional, it is very effective in showing how the cancer is distributed in the breast, and consequently how the patient will respond to treatment. This is the basis of a current national clinical trial on MRI. If neoadjuvant therapy eliminates a tumor on MRI, can surgery be skipped? This might be possible with a well-defined discrete mass. But after a tumor has been treated, anything that looks even slightly bright on MR in the vicinity of the original tumor is likely to be residual disease. We are pretty good at this, although it is not foolproof and there can be a negative signal after complete treatment. Are there other screening techniques that are useful? Even mammography is a better localizer than a screening tool. Other techniques include infrared, optical imaging, optical density scan, and electrical impedance. A really good technique would be one in which we could eliminate at least half the people after screening. The best candidate for this in the future is proteomics, in which we look for patterns as opposed to specific markers. Next month: “Quality of Life: Strategies for Living
Well During Treatment”, Wednesday, April 9th at 6:00-7:30 p.m. |
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