Doctor Nicholas Burris, MD, assistant professor of radiology and director of aortic and structural heart imaging at the University of Michigan Health, talks about a new technique that is helping doctors identify aortic aneurysms, and other potentially fatal heart conditions, before tragedy strikes.
Interview conducted by Ivanhoe Broadcast News in February 2022.
How long has this research been going on?
DR BURRIS: We started this research in 2017. We first came up with the concept for the invention that underlies the technology, and we filed a provisional patent application in 2017 for encompassing the idea behind the vascular deformation mapping technique. Since that time, we’ve been working both with investigators here at University of Michigan and with some scientists at a medical image analysis company called Imbio. They’re a medical imaging analysis company that has several other FDA-cleared technologies that look mostly at the lungs. This is a slightly different application for them but still within the overall scope of what they do.
Who funds the study?
DR BURRIS: The study, right now, is funded by the NIH, the National Institutes of Health. We have a grant called an SBIR – Small Business Innovation Research Grant – with the NIH that funds the collaborative work between our group at University of Michigan and Imbio to develop this technique, validate it, show that it’s accurate, that it’s reproducible, that it tells us something useful about the scans, and then, to build a commercial version that can be deployed at different hospitals across the world and across the country.
Is that the goal?
DR BURRIS: Absolutely. I mean, I am a practicing cardiothoracic radiologist and I think the idea behind the VDM technique came out of my daily frustrations and difficulties trying to look at these scans over many years and measure very small amounts of change or growth in the aorta. That can be very challenging to do when you’re doing it manually by hand. There’s got to be a better way to use a lot of the technology that we have now to do this very simple task in a much more sophisticated way. My goal, as an end user and the inventor, developer, and person overseeing this technique, has been always to bring this back to something that can be used day-to-day in the clinic to help patients.
What exactly are the raters doing and looking for? What does the mapping do?
DR BURRIS: The CT scan comes out with these two-dimensional images, and they’re stacked on each other. From that, you can see the whole structure of the aorta. The problem is the aorta curves, and it goes through these images in an oblique way. The way that we assess for growth of the aorta is we take digital calipers on the computer screen and measure between two points. It gives us a distance of the line and the diameter of the circle. We use that at one time point and then, we have a subsequent scan a year or two later. We measure, do the same technique, and try to do it in the exact same way so that they’re as close to comparable as possible, and then, we’re just looking for a difference in the diameter of those two lines. As you can imagine, you could place it in a slightly different location, and all those things don’t have anything to do with growth at all, they’re just the way that you measured it differently than someone else, or even yourself, at a different time and day. We’re often dealing with about two millimeters’ difference, oftentimes in your measurements. That sounds really small, but the aneurysms grow at about half a millimeter a year, or sometimes, up to a millimeter a year, but that’s considered pretty fast. So, we’re dealing with the problem where we’re trying to measure something that’s really minuscule with these measurement tools that are not able to confidently see that degree of growth. So, the way that VDM works is it takes the full 3D dataset, or the 3D image. It doesn’t require these two-dimensional planes to be made and diameters to be drawn. Now, the challenge is you have two different scans at two different times and the patient could be laying differently on the scanner, they can be in a slightly different position. This is where the technique that we’ve developed really kicks in. It brings the two time points together, the aorta at time one and the aorta at another time in the future, brings them together and compares all the points along the aorta and does something we call registration. Once that registration is complete and the computer algorithm has aligned those two time points as well as they can, the difference where they don’t align is the growth. That’s what we map with a colorized 3D model. We can display the growth of the aorta with an accuracy that’s under a millimeter, probably in the order of a half a millimeter, with this technique based on some of our recent publications.
How much better is that than having a rater do it, based on a 2D or a flat image?
DR BURRIS: The rater are about two-millimeter accuracy and we’re at about 0.5 millimeters, so it’s multiple fold more accurate. One of the papers that we’ve just published shows that we put the algorithm head-to-head against two of our best analysts that work at the hospital that do this all day, every day. They’re really experts. We set the experiment up so that they had the best chances of making the measurements possible. We made it a best-case scenario, and we outperformed them by over a millimeter in accuracy, given the kind of best-case scenario.
In layman’s terms, what does the VDM do?
DR BURRIS: The scanner makes a two-dimensional image and then it stacks up. It’s basically taking cards and then it stacks them all up into a deck. That’s how we view it as we’re going through it as radiologists. Then, you can use software to make what we call reconstruct images to view it in a slightly different plane. But the VDM takes all those cards and turns it into a 3D dataset. So, it doesn’t have to follow those two-dimensional card planes. It can look at the aorta in a completely three-dimensional way.
What kind of a game changer is this?
DR BURRIS: I think it’s huge. I think patients come in very regularly every year to get these scans. The scans cost money, both for the patient and the health care system. They involve radiation and contrast being injected. This is where it’s most frustrating for me as a physician and radiologist, we frequently can’t tell in these one or two interval scans that there’s been any change. This is reassuring to some extent to the patient, that there hasn’t been any convincing change, but I think we can do a lot better. We want to ultimately be able to say your aorta has not changed at all with a high degree of confidence versus us saying that we don’t think it’s changed, but we’re not really sure, and that can go on for years. We have people in our health care system that have been doing this for almost 20 years, coming back and getting these scans. The long-term objective of this technique is to be able to be much more confident, much more accurate in our growth assessments, and be able to tell very early on, within a year or two, if the patient is on a trajectory where they’re going to continue to grow, have a complication, or need surgery. The aneurysm is incredibly stable, and those people can probably go about very infrequent surveillance or potentially not having to follow up at all.
If you’re asymptomatic, why would you still undergo a CT scan?
DR BURRIS: That’s the challenge with this disease. It doesn’t have any symptoms or manifestations and when you develop a symptom or manifestation of this disease, it’s a catastrophic event. This aorta’s just carrying blood and it’s a tube that’s carrying blood through it. When you don’t notice as it starts to slowly dilate, most times, none the wiser until it breaks. When that tube breaks and it starts leaking blood, what we call rupture, most of those people, up to about half of people will die before they reach the hospital. We’re dealing with something that is silent and potentially, lethal. The other thing that could happen is a dissection, which is another type of rupture, but it’s where the aorta splits in half. Both of those events are catastrophic and life changing. They need immediate surgery to open their chest, replace parts of the aorta, and go on a heart lung bypass machine. The objective is to avoid a severe complication. Our cardiac surgeons will oftentimes electively replace the aorta. So, they’ll go in and remove part of the aorta that’s aneurysmal, put in a piece of graft or a synthetic tube that will fix the aneurysm before something bad like that happens. But in any of those scenarios, short of a complication happening, patients are almost always asymptomatic.
Can you just explain what happens with an aneurysm?
DR BURRIS: Most people don’t know they have an aneurysm. They get imaging for something else. They’ll get an x-ray or a CT scan or sometimes even an ultrasound, an echo of their heart, and we find that there’s an aneurysm or the aorta is dilated.
So, is this technology geared toward people who find out that they’re having an aneurysm when it’s too late?
DR BURRIS: Well, the aneurysm grows slowly over decades. It’s like a balloon that’s being progressively inflated until the point it pops. But we don’t know when that point is. Sometimes it stretches a lot; sometimes it stretches a little bit before it pops. That’s the guesswork we know once it gets to a size, which is for aortic aneurysm is about 5 1/2 centimeters, that the risk of that aorta rupturing, or popping is much higher. We don’t know exactly when that structure is going to pop and collapse, so we will follow people. That’s the point behind doing these scans every year. Watching the size, making sure it’s not growing, if it is growing, watching it even more closely. Then, at some point, the decision has to happen between the patient and the surgeon to do surgery. The surgeries, even though they’re done as elective procedures, are substantial. You have to have your chest opened and go on a heart lung bypass machine. It usually involves weeks, if not months of recovery. What we’re trying to figure out with this technique is who really needs that surgery and who doesn’t. Right now, we’re using diameter measurements to make that assessment. It’s well-recognized that those diameter measurements don’t do a very good job at predicting who is going to have something bad happen and who’s not.
Is there anything else that’s important that you would like to add?
DR BURRIS: The areas that are growing are the red areas, and the yellow is slow growth, and the green area is the stable part. One of the decisions that surgeons have to make is when they go to repair the aorta, they have to repair all of the diseased tissue, and try take out as little of the healthy tissue as possible. In this case, the patient had this ascending aortic aneurysm, which was growing. They wanted to know if they had to replace this part of the aorta called the aortic arch, which has blood vessels that go up to the brain, or if they had to replace this part of the aorta, which is called the root, which is connected to the heart, and this is where the valve is, the aortic valve. Our three-dimensional growth map from VDM shows that this root was not growing at all. The arch was growing slowly. This part, beyond that was quite stable. I think beyond just giving patients more confidence in the measurements, there’s also implications here, although we still have to research this and develop the evidence behind it, for how this three-dimensional growth map can be used to better plan surgery, take out all the diseased tissue while not taking out any excess tissue that’s otherwise healthy.
END OF INTERVIEW
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