The speed of 16-slice (and beyond) CT is enabling exquisite images of the heart and its vessels, previously impossible because of the motion artifacts created by the beating heart. The prediction is that it will eventually displace most cardiac catheterizations. How can radiologists adopt this modality and establish a role for themselves in cardiac and vascular imaging? Recently, contributing writer Seleen Collins had an opportunity to discuss this issue with J. Bayne Selby, Jr, MD, professor and interim chairman of radiology at the Medical University of South Carolina, in Charleston.
|(From left) Renan Uflacker, MD, director of vascular and interventional radiology, and Bayne Selby, Jr, MD, professor and interim chairman of radiology, Medical University of South Carolina, Charleston.|
IMAGING ECONOMICS: Tell us about how the Medical University of South Carolina (MUSC) radiologists started using multidetector CT for calcium scoring and were able to reacquaint themselves with the vessels and anatomy of the heart with this technology.
SELBY: As we came into the multidetector CT era about 10 years ago, our then-department chairman wanted us to get into calcium scoring, and he ended up asking the vascular/interventional radiology division, including myself, to do it. To be honest, we were not really excited about it at the time and also were not sure how scientific the calcium scoring was, even though a lot of people were doing it. But we knew that the most appropriate place to investigate this sort of thing was the university setting, so we started doing it.
It turned out to be great preparation for where we are now. By doing the noncontrast scoring examination, looking at calcium in the coronary arteries, we got to review our knowledge of cross-sectional anatomy of the heart – all the nuances of it – which you don’t get as much of a chance to do these days. And we were seeing a very large number of patients. The cardiologists, cardiac surgeons, family practitionerseveryone sent patients in.
|3D frontal view demonstrates three vein grafts and a left internal mammary artery (LIMA) graft. Note the two stents in the distal left anterior descending (LAD) artery. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
IMAGING ECONOMICS: How did radiologists’ use of calcium scoring and CT technology progress from that point?
SELBY: In addition to individual referrals, we added calcium scoring to our MUSC executive health screening program. And then multidetector/multislice CT got better and better, and by the time it got up to a quad scanner, we realized that we could get some pretty good pictures of the heart with contrast. But although the images were pretty neat, they were not anywhere near diagnostic quality for the coronary arteries, unless you really got a good case. However, it was clear to us that this should be the next area to start investigating.
It also made us realize that as soon as they came out with 16-slice scanners, we needed to be first on the block to get one, because we knew that the jump was going to be even greater than going from a single to a quad.
|A lateral view maximum intensity projection image demonstrates anastamosis of a LIMA graft with LAD. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
And again, we were prepared: we had worked with the 3D workstations, which are an integral part of this whole processyou absolutely have to have a great workstation and the ability to use it in order to get the information you require. So to get ready for the next step, we tested some patients who had coronary artery bypass grafts [CABGs] on the quad and found that we could see the grafts pretty well, even though we couldn’t see the native coronary arteries quite as well.
IMAGING ECONOMICS: And now you have a 16-slice CT scanner?
SELBY: Yes, we had this installed about a year ago. At that time we had just moved some of the cath labs and radiological angiography/interventional radiology labs into a Heart and Vascular Center that the university had decided was an important facility for us to develop. It has turned out to be a great thing; the center is an amazing example of cooperation between the cardiologists, cardiac surgeons, vascular surgeons, and interventional radiologists. As we were designing that, we knew we needed to have a CT machine in there, both for interventional procedures and for the more advanced CT angiography, particularly with regard to the heart. So we got that up and running, and that’s when things really became fun.
We built up our experience, going from calcium scoring to the quad to the 16-slice; and now we were ready, because we knew the anatomy of the heart and the way to use the technology. But it is critical not just to know what you are looking at but also, when you walk down the hall to the cath lab – and compare what you saw on the CT to a heart cath – to be able to talk to the cardiologists and show that you are just as knowledgeable about the physiology and the anatomy. We were able to do that. They would start to explain the anatomy on an image, and to be honest, I think some of them were a little surprised by our knowledge, and it put us on a good footing. A lot of times I think that cardiologists forget that radiologists originally developed cardiac imaging.
IMAGING ECONOMICS: What sort of experiences did radiologists at the MUSC center have when they first started using the 16-slice CT scanner?
SELBY: Early successes are always important when introducing new technology. We imaged some patients who had CABGs, and one of those patients had already undergone two heart caths postsurgically at separate facilities and was going to undergo surgery again because the grafts were occluded. The surgeon asked us to do a CT so he could see the sternum and the rest of the anatomy and be prepared for any problems he might encounter. Not only were we able to show him the sternum and the location of the heart, but also we found that two grafts were still patent. The reason they had not been visible on the two heart caths was that they were in places that were slightly unusual, slightly off of the aorta. So that was an early experience in which everyone said, Wow, that’s great!’ That showed a very immediate, legitimate use for multislice CT. Sometimes we are pushing the envelope when we’re trying to see what sort of application is useful, but this clearly is useful right now.
IMAGING ECONOMICS: What applications are you using the 16-slice CT scanner for now?
SELBY: We have the ability right now with 16-slice scanners to evaluate CABGs and really help out the cardiologists and cardiac surgeons. So our CABG patients have been a major source of referrals from them.
With the CT scanning we can help not only to establish the status of the graft but also to answer many other questions. If a patient has undergone surgery and is still having chest pain, there’s always the question as to whether this is chest wall pain from the surgery or a pleural effusion or sternal infectionor is it a coronary artery problem? And of course, CT has always been a great way to look at the chest wall to see whether there is evidence of infection or to prepare for reoperation. The surgeons have their operative notes, but they need to know exactly where the different blood vessels are and how close they are to the chest wall, so that when they make the initial incision, they won’t cut right into a graft that happens to be tethered up against the inside of the chest wall, which sometimes happens.
The CT gives you a big overview of how the chest lookswhether there is pleural fluid or lung problemsand how the heart and grafts look. So, clearly, CABG patients were good candidates for CT imaging.
Another major area we are working on is related to radiofrequency ablations, which have been rapidly increasing under the direction of the new chief of the cardiology department. When you do radiofrequency ablations for arrhythmias, you burn little sections inside the left atrium, near where the pulmonary veins are, and stenoses in the veins can be a complication. A number of investigators have shown that CT is a great way to follow up to see if you have a pulmonary vein stenosis, which can lead to clinical problems. So you may have solved the arrhythmia, but another problem has developed if the patient has a stenosis of the pulmonary vein.
For radiologists who are just starting to use CT, a case like this is an easy way to get good, quality images, if you are using a 16-slice scanner. It’s easier than starting off with the coronary arteries themselves.
So we see a lot of patients now in the post-radiofrequency ablation group. We see them to make sure that they are not developing a pulmonary stenosis, because that can be clinically silent until it gets to be really bad. It’s nice to be able to detect it, because then as a treatment the cardiologist can put a stent in the pulmonary vein and thus fix the problem before the vein completely closes off and before there are problems with blood return to the heart.
This area also yielded another of our early successes. We imaged a patient in whom they had placed a stent because of a pulmonary vein stenosis, but because of the patient’s symptoms, they were afraid the stent had closed down. We performed cardiac CT and were able to show that the stent was wide open. This paved the way for everything else.
We were also able to do some nice 3D reconstructions in this case; with one of the workstations we actually did a “fly through” image of the left atrium, through the stent, into the peripheral arteries, and could show the physicians that. We talk about how we can obtain “pretty pictures” with multislice CT, but you have to ask, are they clinically useful? The fly-through technique has not become really clinically useful, but there is some validity to it. You don’t have to do it all the time, but there is something to showing the referring physicians a movie as you fly through the stent. It does make an impact: they may have believed you before, but they really believe you now!
Cardiac surgeons have actually commented that we shouldn’t be so quick to dismiss these great 3D pictures of the heart as simply “gee-whiz” pictures. They say it is extremely useful to be able to rotate a 3D reconstruction and to see how things relate to each other, before an operation. If you’re the guy who is going to be holding the patient’s heart in a few minutes, it’s nice to be able to see the whole thing from the outside first.
IMAGING ECONOMICS: Has the MUSC Heart and Vascular Center been successful in creating an environment that is conducive to interspecialty collaborations?
SELBY: I honestly believe that if our CT was sitting in the middle of the radiology department, we wouldn’t be doing as much cardiac imaging as we do now at the center. We don’t do a huge number of cases, but we average one or two cardiac images a day, and some days we do five or six. That’s actually a lot for cardiac CT, and I think one of the reasons is the location.
Putting the CT scanner in the center got us off to a good start. There’s the perception of good service and quality in relation to the center, and I think a lot of the reason why cardiologists and surgeons like to refer patients there is that it’s just easier. The practical aspects of that are true, since it is centrally and conveniently located, but there are subjective aspects to this too. Even though radiologists are the ones doing the CTs, the cardiologists and surgeons think, well, they are being performed in our center, the Heart and Vascular Center, instead of some unrelated place. So that has been a big help to us in getting this going. I think this sense of ownership is important. The physicians like knowing that their heart patients can be cared for in one place.
|Patient underwent right heart biopsy with subsequent left anterior descending (LAD) coronary artery-right ventricle fistula. Arrow marks site of fistula. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
It’s also great that we can talk to everybody right away. We have a holding area for patients in the center of the space, with the area for heart CT and angiography on one side and the area for heart caths on the other side. So if I need someone to look at something, the images are all right there. In fact, it has not taken long for there to be a desire for even more connectivity: one of our head cardiologists wants to be able to project the 3D CT image of the heart on one of the screens in the heart cath lab during the cath, and we have our information technology people looking into that right now.
The center is located within the hospital but has a floor of its own, and it handles both inpatients and outpatients. The outpatients go into a nice waiting room from the front entrance, and the inpatients come in through the back entrance, which connects with the rest of the hospital.
|Patient underwent right heart biopsy with subsequent left anterior descending (LAD) coronary artery-right ventricle fistula. Origin of left main coronary artery shows enlarged LAD in relation to circumflex artery. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
IMAGING ECONOMICS: What role does interventional radiology play?
SELBY: Vascular interventional radiologists are doing all the cardiac CTs in the Heart and Vascular Center. At some facilities there is a division-of-labor issue of radiology versus nonradiology, but here we think radiologists are fully capable of doing everything: there’s no reason that radiologists shouldn’t feel perfectly capable of doing cardiac CT. And the other thing is that within departments of radiology, you expect to see specialists within different imaging areas. We’re hoping that there will be a resurgence of interest in cardiac imaging and that 5 years from now you’ll see a lot of people identifying themselves as cardiac radiologists again.
Within radiology, it will depend on individual institutions’ decisions about who is best situated to take this on, whether it’s a CT body imaging group or a vascular interventional radiology group. At our facility, vascular/interventional radiologists are doing cardiac imaging for a few reasons. One, we initially began doing the calcium scoring; two, we had a close relationship with the Heart and Vascular Center; and three, our physical proximity was useful for referring physicians. You can make arguments for body imaging and others for vascular/interventional, but the important thing is to be sure you have dedicated, invested radiologists developing this cardiac/coronary CT.
So, as to the division of labor, nobody else reads the scansonly radiologists. This is how it works: as you begin doing cardiac CT imaging, you do need more physician involvement. The CT technologists are very good and can do a lot, but for developing and modifying initial scanning and reconstruction protocols, you will really need a physician to figure out what will be best and what you need to be able to see. This results in more physician time at the console and workstation. The ultimate goal will be that the technologists will be able to do more of a complete workup and not only acquire the data but also process it. So when the radiologists sit down to read, they will already have a lot of that done for them and not have to spend so much time drawing little circles around thingsbut in the beginning radiologists really have to do that themselves.
IMAGING ECONOMICS: Tell us more about the indications for multislice CT imaging.
|Axial image describes left atrial myxoma. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
SELBY: We find many indications for using the 16-slice CT scanning: post-CABG evaluation; pulmonary vein evaluation after radiofrequency ablation; and other associated heart problems, such as cardiac tumors, pericardial disease, and anything else in the chest that is related to the heart. Pediatric physicians refer patients with congenital heart disease, for instance. Of course, the gold ring that everybody is reaching for is the native coronary arteries. Physicians want to know when they will be able to see them consistently. We’re not there yet with the 16-slice scanner, but we’re pretty close. This whole thing is evolutionary, and we’re much better prepared than we were, so as soon as we get a 64-slice scanner in here, it will be very interesting to see if we finally have that capability. But even now with the 16-slice we can see the native coronary arteries, and when we can see them well, we see them really well. But when you get a poor study, you can’t say much about it. With the 16-slice you can usually see some of the coronary arteries: almost always the proximal portion and most of the time the mid-coronary arteries. Ultimately, to be able to use this as a regular heart cath exam, you would really need to be able to reliably see the whole distribution of arteries.
|A 3D reconstruction (right) illustrates additional relationship of the tumor to other structures. Courtesy of J. Bayne Selby, Jr, MD, Medical University of South Carolina, Charleston.|
The fact that you can almost always see the proximal coronary arteries is good for cases of anomalous coronary arteries, a congenital problem, because CT is great for imaging thisit finds them without any trouble. This is important in the younger population, and in fact you see the anomaly sometimes in young athletes who suddenly drop dead on the playing field; during heavy exercise the coronary arteries are sort of squeezed, and the blood flow gets cut off. Often there are not a lot of symptoms in those cases, either. So we have a number of those cases referred to us. Most of the time the findings are negative, and we can assure them that the coronary arteries are in the right place. But this is an example of how CT is ready in terms of its capabilities with the native coronary arteries right now.
Also, if a patient has had a stent placed, we can see that in the coronary artery quite well with CT, in addition to stents in main bypass grafts. And we can use our various reconstruction tools to actually see within the stent and tell whether it is patent or not. This is not a proven technique, but it is definitely a major research area right now. Our own early results look very promising for stent evaluation.
IMAGING ECONOMICS: How do the CT visualizations compare with catheterizations?
SELBY: We are definitely not ready to replace heart caths with CT! Although for the most part heart caths are still better, there is one area in which they may not be best, and that is if you can’t find something to cannulate in a CABG patient. At least for a regular heart cath, the angiogram is still superior to the CT image, but just as the capabilities have grown with the technology as it evolved from single to dual to quad to 16-slice, it will be interesting to see if we achieve equality with the 64-slice.
The only thing I think CT is superior for right now is hunting for bypass grafts. Weaknesses of CT are in cases with irregular or rapid heart rates. Typically, we give the patients betablockers to slow the heart down a little bit before the scanning, but even more important is to have a regular heartbeat. What we use to acquire the images is a technique called retrospective gating. Cardiac prospective gating has been around for a while, but with these new scanners, we can use retrospective gating: we can scan fast but in small slice thicknesses, and after we acquire the data, we can go back to the scan and determine the quietest part of the heart cycle in order to select the images for the reconstruction.
IMAGING ECONOMICS: What about the radiation dose?
SELBY: Radiation dose is definitely a hot topic. Everyone is concerned that with the faster CT scanners, more radiation is delivered to the patient. The good news is that everyone is very cognizant of this, and the manufacturers are continuously coming up with protocols and techniques to minimize the dose.
IMAGING ECONOMICS: Are there cost advantages to cardiac CT?
SELBY: The cost advantage is in what it will replace: calcium scoring takes 20 seconds of scanning, and for cardiac CT you need an IV and contrast material, but it is very simple. We do chest CTs here, paying close attention to the vessels, so the cost to the facility is no different than for any other chest CT.
IMAGING ECONOMICS: Who handles what procedures in the Heart and Vascular Center?
SELBY: Both radiologists and cardiologists work together in the same general space, which is a good thing, but the radiologists perform all the CTs and read all the scans. The cardiologists do all the heart caths. A number of times radiologists have perfected a new technique and then nonradiologists think they can do itsome feel this may happen with cardiac CTbut I believe that imaging is best done by radiologists. Our relationship with cardiologists and cardiac surgeons is good because of our ability to understand these images and how best to optimize them.
And there is an advantage to working so close together and being able to consult with each other right then and there when a complication arises. If a patient needs a heart catheterization, we can take him or her right down the hallway into cardiology.
IMAGING ECONOMICS: What is the reading protocol?
SELBY: One thing that is different with this technology is that the reconstructions are absolutely necessary. Axial images are useful, but you must have the reconstructions to access all the data. The attending interventional radiologists learn how to perfect the image to show the right information; there are so many tools to explore the images with, that you could easily spend 30 to 40 minutes playing with them. We do the scanning pretty fast, though: the patient can get up after 5 to 10 minutes, and if the images look okay when we review them at the console, then we can release the patient from the clinic. After the procedure, we do the reconstructions and manipulations with the data, and then we sit down with the resident and produce a standard imaging report.
IMAGING ECONOMICS: What lies ahead for cardiac CT, and what role will radiologists play?
SELBY: The referring physicians want to know that radiologists doing cardiac CT are a dedicated unit. At our institution they will write a request for a scan to be done in the Heart and Vascular Center. They like the increased efficiency the center offers, along with its proximity and the comfort it offers their patients. This has been critical to its adoption as a referral site. The referring physicians know what the scanners can do and that the results will come quickly and the process will be smooth, so we are well established. There are many other ways of developing cardiac imaging, but these same basic principles must be followed to have long-term success.
The radiologists here have been doing CT angiography for 5 years or so, along with calcium scoring and noninvasive multislice CT imaging of abdominal vessels, for instance, and that is how we got into cardiac coronary work. It is important for radiologists to be able to work with any group, be it cardiologists or cardiac surgeons or primary care physicians whoever is interested in noninvasive imaging of the heart. But you have to be able to do the procedure: if you’ve practiced and studied, you’ll know you can perform well. Just do your homework; the equipment available now is fantastic.
Manufacturers are continually announcing the next generation of scanners: now 40-slice and 64-slice. These should offer a significant increase in our ability to image the heart.
We can replace a lot of angiography now with noninvasive CT. The revolutionary changes in CT, especially with the 64-slice scanners, will do away with a lot of invasive diagnostic angiography studies. However, it will probably increase interventional procedures with balloons and stents. The CT scanner is not an interventional tool, so we won’t be able to take care of the heart during scanning, but it will prepare us for treating the patient. Right now, for a patient with chest pain, we might do a heart cath after the basic workup, but in 5 years, after the workup, we will do CT angiography instead.
IMAGING ECONOMICS: What is to prevent cardiologists from taking over the imaging component and begin reading like they did with echocardiography?
SELBY: Like echocardiography and heart catheterization, it could happen, but I hate to make it a self-fulfilling prophecy.
The question radiologists might ask is, Why bother to learn cardiac CT?’ Some may view this as simply a turf battle, but if radiologists learn this and are doing a good job, then they should be the ones doing it. What I suggest to radiologists is to reinvest yourselves in cardiac imaging: take the time and effort to open up brand-new horizons for yourselves, and your jobs will get more interesting. After all, it’s fun to do new things and especially things that help people. And when the patients leave the CT procedure room, you will hear them say, Boy, that sure was easier than a heart cath!’
Cardiac imaging will be undergoing a renaissance; in fact, it has already started. Radiology can and should lead the charge. If radiologists sit complacently on the sidelines, someone else will step up to the plate.
The Manhattan Project
Dieter Enzmann, MD, is a man with a mission. As coordinator of the newly formed Manhattan Project for Cardiac Imaging in Radiology, he envisions a not-too-distant future in which all radiologists will feel comfortable performing cardiac CT.
This project is a practical approach to the question of how to train radiologists to perform and interpret cardiac CT and MRI scans, says Enzmann, who is the Leo G. Rigler Chair and Professor of Radiological Sciences at the David Geffen School of Medicine at UCLA. “The goal is not political, but simply one of training,” he notes. “The program is practically oriented: rather than involving lectures, it is a hands-on approach to enabling cardiologists and radiologists to become capable of performing cardiac imaging.”
The project is inclusionary rather than exclusionary, Enzmann emphasizes. “It is supportive of cardiologists as well as radiologists and of their working together in programs collaboratively.”
The Manhattan Project is backed by the Society of Chairmen of Academic Radiology Departments, or SCARD. “With academic leadership behind the program, it is likely that the commitment
to training faculty will be greater. We hope to get most of the academic departments on board within the next 18 months.” Once training at academic centers is complete, the next priorities will be to educate residents, radiology trainees, and radiologists in the field.
The project was conceived a year ago and is still in the early stages of development, says Enzmann. “We are in the process of developing a Web site that will be part of the SCARD site, where prospective participants can search for and evaluate training programs,” he explains. “A related goal is to encourage standardization of training. A concentrated training program will enable radiologists to keep abreast of the technical and clinical developments in the imaging field and to prepare for its consequent growth.”
Seleen Street Collins is a contributing writer for Decisions in Axis Imaging News.