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Radiology Today
Interview Steven E. Harms, MD, FACR, is an MRI researcher and clinical radiologist with The Breast Center of Northwest Arkansas in Fayetteville. He is a developer of the RODEO (Rotating Delivery of Excitation Off-Resonance) MRI technique, which is commercialized as SpiralRODEO software available on 1.5 Tesla breast MRI systems developed by Aurora Imaging Technology, Inc. He is a strong advocate of breast MRI and recently spoke with Radiology Today about the technology and the growing role of breast MRI. Radiology Today: Breast MRI certainly is a technology doctors are using more in breast cancer diagnosis and staging. The RODEO technique you and your colleagues worked to develop offers higher resolution images. How is it different? Steven E. Harms, MD, FACR: A standard MR image is usually obtained by a method called Fourier Transfer imaging. For most breast images, it’s 3-D Fourier Transfer (3DFT) reconstruction imaging, where you build that reconstruction space one line at a time. If you wanted to have 128-pixel resolution, it would take 128 projections of that image. If you wanted to double it to 256 pixels, it would take 256 projections to make an image. And that would be multiplied by however many slices you want to have. If you have 64 slices, that’s 128 pixels or 256 pixels times 64 slices. With spiral, we’re not building reconstruction space one line at a time. In fact, we start at the center of the reconstruction space and spiral all the way out to the periphery. You could calculate an image with each spiral if you wanted to. You would not have to do multiple projections.… For breast imaging, we want high contrast and high spatial resolution. We’re doing 512 X 512 imaging with 32 projections. That is significantly more efficient than 3DFT, where we would have taken 512 projections. We typically do 160 slices, so our resolution submillimeter in all directions. Most breast MR imaging does only 64 slices. Radiology Today: What does that mean in terms of the resulting images? Harms: We get three times the signal-to-noise ratio (SNR) of most 3DFT images. We’re using that SNR to improve resolution and improve the contrast resolution. And there are significant gains in both of those. The image resolution by the number of voxels we generate is three times that of what we had before. We also reduce scan time, which is less than half of what it was and contrast is about twice what it was before. It’s a considerable gain. In an MR image, the center of reconstruction space contributes most of the contrast. Typically in 3DFT, you only pass through the center of reconstruction space in the middle of the scan, so the middle half minute of data collection is the most important. With spiral, we’re scanning the middle of reconstruction space on every projection so, in effect, you get oversampling of the contrast part of reconstruction. That gives you a very solid contrast appearance. You don’t have a noisy type picture. On a typical MRI scan, you run pretty lean on signal to noise. You push the resolution as high as you can get it until you start to see noise on the image and then you back off a little bit. You tend to operate MRI right on the edge of the noise. MRI is usually lower contrast to noise than a CT, which traditionally has tremendous [SNR] and very solid contrast. But this spiral MRI technique produces such solid contrast that CT-type image processing techniques, such as surface renderings or volume renderings, are easily done. You just can’t do that with standard MRI. I think it’s a revolution in platforms. When the first multislice CTs came out, I thought, my gosh, why hasn’t everyone done this in the past? It’s such a logical thing. You get two slices instead of one; you double your image-gathering efficiency. And now when you go to RSNA and there may be some 128- and 256-slice machines. It’s exponential growth, but the key thing was the realization that we don’t have to get one slice at a time. Radiology Today: Will the spiral technology be applied to whole body machines? Harms: It’s a broad new platform that probably ought to be embraced. But spiral requires a completely different set of gradients. We just don’t have them for whole-body systems. That’s why it makes sense for it to be used with a dedicated system. We don’t have to worry about echoplanar imaging in the breast. We don’t have to worry about doing MR angiography. All we have to do is make the best quality image of the breast. Radiology Today: Who is using breast MRI? Harms: The trend is toward consolidating expertise in breast centers. There is a lot of mammography done by radiologists who really don’t do very many mammograms. Probably the best analogy that I can give is ultrasound. If you did the mammogram and then sent the patient to a different center for her breast ultrasound, the breast ultrasound usually will not have the same quality as the center that does both mammography and breast ultrasound. The same applies to breast MRI. It is a key thing to put the MRI in the same place with the expertise and the patients, so the physicians integrate the MRI with the other imaging and manage the patients. Radiology Today: So breast MRI really isn’t for the community hospital that just does mammography screening and refers other work along? Harms: The number of places that are MQSA (Mammography Quality Standards Act of 1992) breast centers, which is just about anyone doing mammography, has actually gone down in number. There has been a consolidation. The centers that are really not very interested in breast care are falling by the wayside. Aurora’s system and breast MRI in general will grow in places that have already developed a breast care market. Radiology Today: Clinically, where do you see this system fitting into a breast radiology practice? Harms: When the American Cancer Society comes out with its new guidelines on screening—maybe before the end of the year—they will include breast MRI as a major application for women at high-risk for breast cancer. Most insurers are paying for breast MRI in high-risk patients and that has moved it into the mainstream. It is now common to do breast MRI in many breast practices. The use is probably growing as quickly as any application in MRI. Radiology Today: Besides its growing role in screening, how is breast MRI used? Harms: The usual place to start is the patient who has a diagnosis of cancer and you are looking to better determine the extent of the disease.… Studies have shown that 30% to 50% of patients with a known cancer prior to treatment will have a change in management as a result of their MRI. I can’t think of a single MRI application in any other body part that has as much effect on management. It’s rare to have a treatment change with spinal MRI, and that’s our most common MRI exam. The next step is characterization. These are people with difficult-to-interpret mammograms or sonograms—where you need the high court of breast imaging. MRI is the most sensitive test for breast cancer. If you can clear certain lesions or determine that you do need to go on to biopsy, that is an important step. The last use for breast MRI is screening people that have no positive exams. That group typically includes people whose mother or sister died of breast cancer and they are very anxious about breast cancer. Using MRI, where you’ve got a negative predictive value of close to 100% and can exclude breast cancer, is extremely valuable in those cases. You can tell a patient that, in all probability, they don’t have cancer and don’t have to have another exam for another year unless they have symptoms. It’s a great burden lifted off their [life], so it is an extremely valuable tool there. Radiology Today: Are there types of cancer where MRI does a better job than other technology? Harms: The real battleground in breast cancer now is in those indistinct lesions like DCIS (ductal carcinoma in situ) and lobular carcinoma. The false negatives reported in the screening trials were almost all DCIS cases. DCIS does not exhibit wash-out enhancement curves, so typically it won’t be picked up by most CAD (computer-aided detection) programs. And it looks similar to many proliferative changes that you don’t need to worry about. It’s an elusive diagnosis. DCIS is breast cancer that is confined to ducts and does not spread past the basement membrane; as such it is surrounded by normal breast tissue. So if your imaging has big voxels and you average in normal breast tissue and it doesn’t register with enhancement, in many cases, you will not see at all. With SpiralRODEO, we’re reducing the imaging voxels’ size down to the millimeter and submillimeter range so volume averaging is much less of a problem. At that resolution, you start to see a fairly characteristic morphology of DCIS—a linear branching enhancement in almost all cases. High-resolution MRI is something I ought to define because a lot of people call what they’re doing high resolution and they are scanning with 3-millimeter slices. When I’m talking about high resolution, I’m talking about many orders of magnitude higher than that. We’re talking slices of 1 millimeter or smaller. We’re talking in-plane resolution of less than 1 millimeter. So the voxel volume is less than 1 millimeter in all directions. That allows us to see that branching enhancement. You will not see that with most other MRI machines, but it allows us to make a very specific diagnosis of DCIS. Radiology Today: You also mentioned lobular carcinoma. Harms: Lobular carcinoma is very similar in that it is often very hard to see on MRI. With SpiralRODEO, we see it routinely and accurately display its extent. So now we’re routinely marking margins of DCIS and lobular carcinoma for lumpectomy. Radiology Today: How is MRI changing treatment? Harms: The criticism you’ll often hear about MRI is that when using it, we’re seeing things and converting patients that would have had a lumpectomy to a mastectomy. Critics reason that since the recurrence rate on a lumpectomy is 5% to 10%, we’re already treating people with lumpectomy effectively and needlessly converting patients to mastectomy. Radiology Today: You obviously don’t think that. Harms: What I will say to that is we’re doing the reverse. We’re seeing people who normally would have had a mastectomy because the extent of their disease. By using MRI we are able to mark the margins of the lesions accurately enough that a surgeon can do a tailored lumpectomy and have an excellent cosmetic result. It’s a dramatic change in the way we practice medicine. We recently had a patient with DCIS that if you measured from anterior to posterior involved a linear area about 6 centimeters long. DCIS cases typically run in ductal rays from the nipple to the chest wall. Normally, you would not do a lumpectomy on somebody with 6 centimeters of cancer. If she had been treated with lumpectomy based upon her mammogram or ultrasound, this woman would have had a lumpectomy and afterward they would have had positive margins. Then she may have gone back and had another lumpectomy and still had positive margins because they didn’t know this cancer was 6 centimeters long. The referring doctors thought it was just a small area of microcalcifications. With MRI, we were able to see that it was 6 centimeters anterior to posterior, but it was only 5 to 10 millimeters in the other directions—it was cigar shaped. Using MRI guidance, we’re able to mark those anterior to posterior points of the lesion. Then the surgeon went in and did a tailored lumpectomy taking out a cigar-shaped piece of tissue. The woman had clear margins after the first surgery. She was able to have an excellent lumpectomy result with a good cosmesis. Without MRI, she would have ended up having multiple surgeries and probably a mastectomy. So we saved the healthcare system a lot of money, saved the patient a lot of recovery and unnecessary surgery, and gave her the optimal surgery for her disease. Equally important, we were also able to clear the rest of her breast. We knew that she didn’t have any significant disease in the rest of her breast. The surgical literature has positive margin rates of 50% to 70%. The surgeons know that about half the time they’re going to have to go back in and resect more tissue because they didn’t know what the extent of the disease was before surgery. With MRI guidance, we’ve cut the reincision rate to less than 10% in our patients. Radiology Today: So you are seeing a big difference in your practice? Harms: I practice in a small town.
If you’d come to our breast conference, we probably discuss about
half a dozen patients each week. On average, there are probably a couple
cases each week where MRI significantly affects their management. These
are major savings in terms of morbidity and cost. It’s a bigger
impact than any other application in MRI that I’ve been involved
with and I’ve done all kinds of MRI.… I think every practice
that is seriously involved in breast imaging and breast treatment needs
to integrate breast MRI into their practice. That’s a dramatic
impact to the healthcare system, but more importantly we’ve given
the right treatment to the patient.
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