Q: What do you see is the major role for CT angiography -- is it mainly in the area of heart disease? Some say it's going to replace invasive catheterization.
Dr. Achenbach: I think that you're absolutely right. I mean the role of CT, currently the major focus is imaging of the coronary arteries. There are a few other things we can do, but the major focus is the coronary arteries. And what coronary CT angiography can do very well, if it's done carefully, it can very accurately rule out the presence of coronary stenosis. If a CT scan is normal, of good quality and normal, then you can be very certain that the patient does not have coronary stenosis. And I think that's the main application -- to use it instead of an invasive angiogram, when the patient is symptomatic, or has some other findings that point to the possibility of coronary artery stenosis being present, but, as a physician, you consider the likelihood that the patient really has the disease is not very high -- you kind of have the feeling that the patient should have an invasive angiogram, but you expect it probably to be normal. In these situations, the CT angiogram is extremely useful, and I think that's currently the main application. Using it to avoid invasive angiography in patients who might have coronary stenosis, but the likelihood is relatively low.

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Q: Some physicians, like Dr. Ralph Brindis of Kaiser Permanente in California, have expressed concern that CT angiography may lead to many more procedures being done on people who don't really need them.
Dr. Achenbach: I think there are very valid concerns out there that need to be addressed, and it's good to be somewhat careful about a new technique to avoid overuse, especially in the beginning. On the other hand, we should not be overly critical, and prevent a good method from being used clinically.

I think there are two ways in which CT can be not too useful. First of all, if it is performed on people who don't need it. If you take a completely asymptomatic person walking around on the street, and you do a CT angio on them, well there is a certain likelihood, it's low but it's possible, that you'll find a stenosis. And then there is an almost automatic reflex that, if you see a stenosis, that you send a patient to the cath lab, and then in the cath lab the stenosis is treated. But if the patient had no symptoms ever to begin with, and the stenosis is, let’s say in the left circumflex coronary artery, then treatment of that stenosis doesn't help the patient at all. So it's true, if CT angio is performed in patients who are completely asymptomatic, and really don't need any coronary diagnostics, there is a danger that you'll find lesions that should never have been found, and you send them for treatment which was not necessary. That's one aspect, that it's performed in the wrong kind of people.

The other aspect, and I think that might be at least of the same magnitude, and that's if the CT is not performed well. You know, CT of the heart is relatively stable, but it can be difficult in some instances, and also if the technology that you use is not adequate, it's even more difficult. And if you don't perform it well, if there are artifacts in the data set, then usually what happens is that you see stenoses that are not really there. A CT scan of low quality is usually false positive, and not false negative. So that happens a lot, that if a CT scan is performed, maybe not absolutely expertly, and then the person who reads it might not be, you know, super-experienced, and what happens is that they start feeling a little insecure, and they call a stenosis that is not actually there, and the patient ends up in the cath lab, and the cath lab shows that the CT was false positive, and that a stenosis is not present. So these are the two things that can happen. That's why it's important to have people well-trained in cardiac CT, to use the right equipment, and to also make sure that they don't scan patients that should not be scanned.

Q: What can be done to rectify these situations -- obviously, better training...
Dr. Achenbach: Well, there are many things going on. There are now the guidelines for competency. Level 1, level 2, level 3 guidelines for competency, for what you should have done in order to perform a cardiac CT scan. I would say that these are minimum requirements, but they do guarantee a certain level of expertise before somebody does a cardiac CT -- these have been published by the ACC and AHA, and they call for basically 150 scans interpreted for the level 2 competency, which means that you are able to perform and interpret your own CT scans. I think that's rather reasonable.

People who want to do CT, they just have to go out there and pay attention that they get good training. If they take a course, that its a good course with real experts teaching it. In the end, I think, probably it's going to control itself a little bit. If somebody runs a CT business or a cardiac CT lab and the results that are produced are not good, then the referring physicians will probably turn somewhere else after a while.

Q: Equipment is changing quite rapidly. Just a few years ago, the best was a 16 slice -- now there's 64 slice, and on the horizon is 256 slice, or dual source. Can you speak to the technology advancing, here?
Dr. Achenbach: I think definitely the technology is advancing all the time. And we will continue to see improvements that will immediately translate into clinical benefits. I think we have seen a major improvement going from 16 to 64 slice CT. With a 16 slice CT it's possible to do coronary CT angiography, but it's not easy. You really have to know what you're doing, you really have to scan very carefully. With a 64 slice CT, it became easier. It's really, now, universally do-able, with a 64 slice CT, if patients are prepared well.

There's still the prerequisite that the heart rate has to be low -- you should pre-medicate patients with a heart rate of more than 60, to lower it. That really improves the images a lot. But with a 64 slice CT you can do clinical CT angiography of the coronary arteries with stable results, and that's what's moved the scanning of the coronary arteries into clinical practice. And there are continuous improvements beyond 64 slice CT. The dual-source CT has been available for about one-and-a-half years now, and it has been able to show that scanning of higher heart rates is possible, quite reliably. The 256 slice is out, installed, in prototypes only. But, what I hear, between the lines, is that the overall scan time is shortened quite a bit, to just 1.5 or 2 seconds. But I would say, if you have a 64 slice CT, you're already pretty good, equipped for coronary CT angio.

Q: One of the big concerns from the standpoint of patients, and also referring physicians, is the radiation dose. And I know a lot of work has been done to reduce that, both in the equipment and also in the techniques used.
Dr. Achenbach: That's a valid concern, and it depends a lot on the expertise of the person who performs the scan, You have to use all options that you can to lower the radiation dose to a reasonable limit. If no attention is paid to radiation dose, the doses can be extremely high, 20 milliseverts or more. But this will be avoided if care is taken to keep the radiation dose in a reasonable range. You can probably perform a 64 slice CT routinely between 5 and 10 milliseverts. And, there are even new developments on the horizon, I wouldn't say they are standard yet, that you might go below 5 milliseverts. I think 5 to 10 is very reasonably achievable, and that compares favorably with other tests. For example, nuclear perfusion tests have the same order of magnitude, cardiac cath might be a little less, 3 to 5 milliseverts, but it's the same order of magnitude.

Q: Some of the concern is why do a CT angiogram if there's a good likelihood that the patient's going to need a regular, invasive angiogram and perhaps a procedure, like an angioplasty, at the same time?
Dr. Achenbach: I would absolutely agree. We are all clinicians, and often enough you have a patient in which we are certain, or 95% certain, that the patient has coronary stenosis. In that case, I would not do a CT angiogram. In that case I would go maybe for stress testing or the cath lab immediately. If you know that the patient has disease, the patient doesn't need a CT scan.

Q: There's some research on performing perfusion studies using CT -- do you think CT may replace nuclear testing?
Dr. Achenbach: I think that it will be potentially be an alternative to a nuclear test. I don't think it will replace the nuclear test, because there is so much-- such a large database on nuclear scanning. I mean, if you perform a nuclear radiation perfusion scan, and you have it resolved, then you'll know exactly what it means, you have millions of patients for reference. It's so well established and so well embedded in cardiology, for patients who just purely need a stress test just to test for ischemia -- the nuclear perfusion scan is not going to go away.

There is the option, however, of adding on a CT angiogram plus perfusion scan in one test, and I think that might be a reasonable thing to do in the future. Not at the moment, but in the future, to have a more comprehensive test for the patient. It's in research phases. I mean there are a handful of papers, and each one has a handful of patients. It's too early.

Q: What about imaging stents with CT to see if there's been a reblockage, in-stent restenosis?
Dr. Achenbach: I think that there's not a good answer, because that's exactly at the point right now, where we're going from "it's not possible" to "tt's probably possible." But I would still not say that it’s a routine clinical indication to scan a patient who has a stent, because stents, with the dense metal that they contain, they can create artifacts very easily, and out of my own experience I can say that it's extremely difficult, and often enough impossible, to determine whether there is an in-stent restenosis, because of the artifacts caused by the stents. So I am a little bit on the cautious side, I know it. But I currently do not recommend scanning patients who have implanted stents. There might be exceptions -- if a patient has a very large stent. The larger the stent, the larger the diameter, the easier it is to see inside.

We are seeing some publications now, there was just a publication of about 35 patients from Turkey, there was another publication of about 115 patients, I think, from the Netherlands, and they both saw relatively good results. Sensitivities way more than 90% to detect in-stent restenosis, but there are only very few publications. And then there are others, who have substantially lower accuracies. So, I think we still have to learn, and I would currently be reluctant to recommend CT scanning in stent patients, because the likelihood that you won't be able to read it with confidence is just too high. I might change my opinion two years from now -- I don't know -- but currently I would not consider this a routine application.

Q: How can a patient know whether they're going to the right place? Whether the person, the physician or the company doing the CT scan is going to have a high level, and is there a difference in the specialties? I know radiologists do them, cardiologists do them. Do you have any recommendations there?
Dr. Achenbach: Well, I think volume is important. Whatever you do a lot, you'll do well. So I definitely think the volume is important -- that's one criteria that you should look out for. How do you assess volume? Well, probably they will not tell you exactly that they've performed so many CT scans per year, but I think a large center does about a thousand scans per year. So I would not go to a place that has performed 2 of these tests a month. And also, if the center has one person who is dedicated to cardiac CT -- I know in many centers in the States there’s like one physician who does cardiac CT all day, and that's probably a sign of quality, because if you do it all day, you'll have the experience, the expertise, to do this well.

Whether it's a cardiologist or a radiologist? I wouldn't say that matters. Both can perform it if the volume is high enough, and if they are adequately trained. Then, of course, you have to look for equipment. And a very experienced person can probably do cardiac CT quite well with a 16 slice CT, but usually, I would look at least for a 64 slice CT.

Q: Finally, there's been some discussion that Cardiac CT is going to be able to show the kind of soft, thin-capped plaque, sometimes called "vulnerable plaque". Is that something currently feasible?
Dr. Achenbach: There is increasing discussion about the use of coronary angiography, a contrast-enhanced scan, to find plaque: small, atherosclerotic deposits do not cause stenosis at the moment, but they might cause myocardial infarctions somewhere down the line. Traditionally, this has been done through the calcium scan, but now with the better quality of the scanners, and the contrast-enhanced images, this also allows us to detect non-calcified portions of the plaque. And I know that many physicians are extremely enthusiastic about this, using this for risk stratification. Doing a CT angiogram in asymptomatics who have risk factors, to determine how high is their risk of myocardial infarction. And again, there's lots of discussion about this, and some are doing it -- I personally am very reluctant because I think there's not enough data out there at the moment to support this application.