Applied Radiology

ELLIOT K. FISHMAN, MD: Now that we've heard each of the presentations and had a chance to ask specific questions about them, I'd like to take some time to discuss some overall themes. Within the presentations, we've had a review of standard concentrations of contrast and their use in CTA procedures. We've discussed relevant information on the selection of a contrast agent for CTA procedures. But I'd like to get everyone's advice for others just getting started in CT angiography.

DAVID P. NAIDICH, MD: Well, the issue is that to really do good-quality CTA you need to have attained a certain level of expertise. I think the rate-limiting step for using this technology has been the reluctance­­perhaps on the part of manufacturers, perhaps on the part of radiologists performing routine studies­­to involve themselves with learning to do this type of imaging. Actually, this is consistently getting simpler to do. Unfortunately, despite progress, there is still a gap between our ability to acquire sophisticated data, and the ability to generate the images that would be the impetus for including these as routine clinical procedures. Elliot, you can speak to that better than I can.

When you look at Dennis' pictures, for example, it's clear that an average community radiologist is not out there doing this kind of imaging. So, the question is, why aren't they? It's not because the technology isn't available. We have to determine what the rate-limiting steps are. We need to determine what the sound barrier is, if you will, that we need to get past to get people doing these procedures routinely. That's really the heart and soul of the issue of CT at this point.

Today, we've seen that, in the right hands, CTA is an extraordinary tool in virtually every aspect of the body.

FISHMAN: Are there any specific contrast-related issues, for example, in the chest or in thoracic applications? Do you have any advice on contrast selection that you could share?

NAIDICH: Selection of contrast is an issue in terms of contrast utilization, cost issues, and contrast reactions. When you start talking about pushing 5, 6, and 7 mL/sec, you will have a lot of resistance from a general radiology audience. In fact, there would be a lot of resistance to even going much above 3 mL/sec. That is something that we really need to make clear. Increasing injection rates is not a danger to patients, and it is not necessarily going to relate to renal toxicity. To date, I have not had enough experience with the iso-osmolar contrast agents to render a definitive judgement concerning their use. Reflecting on what I have heard here today, the use of these agents could be extremely important for the general radiologist to understand. Presently, to my knoweldge, these are not being used for general applications, such as pulmonary embolism.

CHRISTOPH R. BECKER, MD: In our department, we have a guideline to give iso-osmolar contrast media to any patient who is coming in with a creatinine level above 1.5 mg/dL. It's incredible, but once the clinicians picked up on the low nephrotoxicity of iso-osmolar contrast agent, they are demanding it, since they are so strictly aware of the nephrotoxicity of any other contrast agent.

FISHMAN: Do you have any other specific words of advice for someone starting off with CTA or anyone doing a minimal amount of it?

BECKER: I have already mentioned that more contrast is not always better in CTA. In particular, in atherosclerotic disease, there is some need to dedicate a kind of contrast application. But if you keep a simple rule of thumb in mind--1 gI/sec--with this amount of contrast you will achieve ideal enhancement of the arteries and vessel wall. Higher flow rates may only be necessary in vessel territories with no calcifications such as pulmonary or visceral arteries.

NAIDICH: I want to say one more thing about contrast. If there is a reluctance on the part of a lot of general radiologists to perform CTA, based on their concern about the complexity of contrast administration­­choosing appropriate timing and doses and so forth­­that should not be a reason for not doing it. There are relatively straightforward rules, especially now with bolus tracking, which should relieve any fear of how complex this process is.

FISHMAN: But there's no doubt that 16-slice CT has made it much easier to be successful than it was with
4-slice or single-detector CT. With 16-slice CT, a lot of the excuses that existed with 4-slice tend to fade away. For most groups starting with CTA, there must be an advocate within the group who takes responsibility for the process: setting the protocols, contrast volumes, timing, and everything else. It's not technologists deciding, Well, let's do this and that, unless someone in the group is very proactive. But too often, if it's someone else's job to do it, it just never happens.

NAIDICH: Well, the extent to which knowledge about contrast administration is an excuse for not using CTA is something that must be clarified. Radiologists must understand that, while there are many potential approaches to performing CTAs depending on clinical indications (eg, peripheral runoff studies), nonetheless, the faster scanners now allow a more uniform approach, especially with bolus tracking. We need to disseminate the message that we should not hesitate to perform CTA because of the potential complexity of contrast administration.

MARILYN SIEGEL, MD : That also sums it up in the pediatric population. Radiologists need more education on how to do CTA in children. CTA works well in a young population if one understands the basics of contrast administration: namely volumes of contrast agent, timing of scan initiation, the use of automated bolus tracking, and technical factors specific for children, particularly the mAs and kVp. Gaining acceptance of CTA in children means providing protocols and training radiologists how to do it.

FISHMAN: It seems to me that you see a reluctance, at least in the literature, of those doing pediatric imaging to really get involved in the 3D components and CTA. There seems to be very little in the literature about it.

SIEGEL: True, there is reluctance about performing CTA in children and, in large part, this reflects the paucity of literature available on the topic. It also reflects the concern about radiation. However, radiologists need to recognize that the technique for CTA in children is the same as in adults, but with minor modifications. If you choose the correct parameters and understand the clinical indications for CTA and 3D imaging in children, you get great results and minimize radiation exposure. We need to provide this information to the radiology public.

SANJAY SAINI, MD: The main thing I worry about is that CT used to be goof-proof. Everybody got the same scan and it worked every time. Now CT has become more complicated. There are a few specific things that I want to mention. First, on every abdominal CT study, whether it is a routine study or a dual-phase study, we use bolus-detection techniques, as I described. Once the technologists get used to it, they will use it in every case.

Second, we have not done enough about modulating the contrast dose with respect to patient weight/size or clinical application. For example, when we scan the kidney for renal mass characterization, we give less contrast than we do for a liver lesion detection study. With the multidose delivery systems now available, this will eliminate waste of contrast and provide cost savings. Third, for CTA studies, we have lowered the tube-potential to 120 to 100 kVp. At this point, however, this change is based on anecdotal evidence rather than scientifically validated data. Finally, we have become comfortable with the automated exposure technique and use it on all abdominal studies with noise index of 15 to 20 HU. This can lower radiation dose by >30% and is especially important in nononcologic patients.

KYONGTAE T. BAE, MD, PhD: I would like to echo David's comments. It looks as though we are still learning, and there is a time lag, perhaps 3 or 4 years, before community radiologists practice and follow the guidelines drafted and experimented with by leading academic institutions with state-of-the-art technology. Dennis' protocol doesn't even include single-slice CT, but there are many places that only have single-slice CT scanners for CTA. Until we figure out and provide some consistent guidelines, it is natural for community radiologists to be reluctant to practice CTA. Perhaps, an automated injection protocol and scan system may relieve some of the stress of trying to figure out an optimal imaging protocol. I think it will definitely help general radiologists accept CTA as a routine test.

FISHMAN: You had a very detailed analysis of contrast administration and choosing agents. Do you have any short words for people getting started, especially on choosing agents?

BAE: In our institution, we use 350 mgI/mL, that's the highest concentration contrast we have. For all CTA, we would like to use the highest concentration we can get. For scan timing, we advocate a bolus-tracking method instead of a test-bolus method. But then, the next issues become: what enhancement triggering threshold value do we need to select? What additional delay should we add for a fast scan? We are still in the learning curve. I don't think we totally understand the most consistent and effective way to perform CTA. I hope, after this meeting, we'll come up with more conclusive suggestions. But I expect there will be a lot of trial and error until we can determine a definitive technique that everyone can use with all scanners.

FISHMAN: I want to make an important point. I don't think people need to wait until all the answers are in on CTA, because by the time all the answers are in, there will be another detector starting the questions all over again. So, for all radiologists, if you are going to do CTA, now is as great a time as any. Will things change? Will we learn more? Of course. It's like a Don Henley quote, The more I know, the less I understand. All the things I thought I knew, I'm learning again. That's very true; it is a constant learning process. But there is no sense putting it off. As we've shown this morning, the capabilities are incredible.

S. JAMES ZINREICH, MD: If you take a look at neuroradiology, it is a little different. That is, it's not the technique or the protocol that really makes a difference; performing an examination is done with relative ease. The question is, are you going to use CTA versus MRA? You have to evaluate the patient population that you are dealing with--for example, the stroke patient. In this case, you are dealing with an elderly person who had specific symptomology and who has already had a CT examination. The patient is on that table now; you are dealing with a critical time period. We want to make a diagnosis within 3 or 6 hours. You can't afford to play around by going to MR and angiography. You need to be able to make a diagnosis as soon as possible. Therefore, doing a CTA examination really makes sense and ought to be the very next step. So if I have a stroke patient on a CT table, I'm contemplating or diagnosing stroke. Am I dealing with vascular stenosis? The next step ought to be automatic­­I'm doing a CTA examination, and whether the patient is renally stable or not has to be taken into consideration. It's the same thing with subarachnoid hemorrhage. You are dealing with a patient who isn't healthy, who is not going to be able to cooperate with an MRI examination and hold still for an extended period of time. You know there will be problems. So, when I'm dealing with a CT, the next step ought to be a CTA. If I'm having problems with the CTA, I ought to go to the next steps, and contemplate whether I am going to do a DSA or an MRA in order to improve my diagnostic capability. When we're dealing with difficult, elderly, sick patients, in whom CTA makes sense, it ought to be the second thing that you think of immediately after performing a CT examination. You also deal with another set of patients--head/neck patients. CT is very important in that patient population. When you do CT in those patients, contrast has to be given. Without contrast, that examination is worthless.

BECKER: We've had a new development in our department. Recent literature has shown that, in patients with early strokes (up to 3 hours of onset), you can see the stroke on the source images of the CTA, pretty much in the same fashion as we see it on diffusion-weighted images. Indeed, we have pretty nice cases on this, in particular during the night, we are doing this in many cases. So I think this is a boost for CTA in these particular patients as well.

ZINREICH: Perfusion, yes.

BECKER: It's a kind of perfusion, but to be more accurate, it's blood-volume imaging. It's really showing you the core infarction area, even in the absence of any early stroke sign on the other scans.

ZINREICH: Right, estimating the original blood volume, absolutely.

BECKER: The difference of enhanced density is in the range of 20 HU. It is unbelievable to me that this is even coming up now with multidetector CT, because we've had this kind of technique available since the start of CT, 30 years ago. But, as we are now using the high flow rates with multidetector CT, it becomes so obvious that this enhancement is in the healthy tissue and we are taking advantage of this for stroke assessment.

ZINREICH: The topic at the moment is CTA, and I didn't want to get into the perfusion CT studies. But, obviously, that is the very next step to follow. Therefore, you would have the entire information about this stroke patient, and, most importantly, you would have it very quickly.

FISHMAN: I also want to make one point between the neuroimaging applications and, eventually, the cardiac applications. Medical centers are moving CTA to the ER, particularly in a place like NYU, where they have the 16-slice scanner in the ER. In the past, typically the worst scanner was in the ER, one of the older scanners. Now you may actually need your best scanner in the ER, because so much of our work really comes from that direction these days. I think that roughly 60% of the admissions to Johns Hopkins come through the ER. You can do a lot of the work before the patient comes in. But it is a big source of most hospitals' patients.

W. DENNIS FOLEY, MD: I want to pick up on what David said about how to get CTA accepted. I agree that you need a champion within the radiology group. Another thing that is probably going to happen is that the vascular surgeons and other surgeons will come back to the radiology department, and ask the radiologist to do what they have seen presented at their vascular surgery meetings. So that will have some impetus in increasing the use of CTA. In terms of IV access, which is just a simple thing, we have a portable ultrasound machine in CT that we use for getting IV access when the technologists can't find it. Another simple thing about injection is that we always have the patients put their faces up, with their hands up against the face of the gantry. If the arm is back, you get an inadequate injection in many cases.

About the 3D renderings, we do have the remote 3D lab, and I know we're the champions of it. I agree that radiologists should be much more involved in making 3D images. So we are going to force ourselves to do it by putting a Windows workstation right next to our PACS diagnostic workstations. Ultimately, the manufacturer will make 3D data sets at the console, which they will basically send out to radiologists, automated.

SAINI: Dennis, who has the time to make all those 3D images? I know Elliott takes 60 seconds to do it, but if you are reading 50 CT studies a day....

FISHMAN: Right now, the problem is how things are structured: you have PACS systems, so we do PACS; you have 3D systems, and we can do 3D. It is incredibly inefficient. If you have technology where everything comes up on one system, we would be in the 3D world immediately. Basically, everything we are doing now is volume acquisitions. So you are reconstructing by ones and reconstructing by fives, and sending this here and this there. But the reality is, if you just get a thin section and send it to one place, you could do everything from the axial, the multiplanar, and the 3D images interactively, at a rate of 15 or 30 frames a second.

SAINI: But is this really needed for diagnosis?

FISHMAN: It depends on the situation. If I'm staging lymphomas and looking for nodes, honestly, the multiplanar images may be nice to look at, but the axial images will give me all the answers. But more and more, our practice, I think, is like yours--we do so much oncology staging.

But there is also the issue of our referring physicians. For example, John Cameron is a surgeon at Hopkins who has done a thousand Whipple procedures, and now he will not do a Whipple without a CT angiogram. It becomes very cost-effective since there are no other studies done, and the clinicians really rely on them.

One of the things I noticed is that no one ever questioned us doing 3Ds per se; it was never an issue. Now it's gotten better, faster, and easier. Now the first question clinicians have is, How can I get one of those machines in my office? They really don't want to see the axial images. Right now, we create a thousand images, but who wants to see them? They just want to see the images that show their pathology and 3D does that incredibly well.

SAINI: But if that is the case, then the 3D images are really used to capture the information, not make the diagnosis.

FISHMAN: Well, it's both. We have a paper coming out in Surgery about this. I read 3D images for all pancreatic patients before they went in for potential surgery. Typically, if you do imaging of the pancreas, it's approximately 70% accurate in determining who is resectable. We read them all preoperatively, and then they went to surgery. We found then that the preoperative 3D imaging was roughly 93% accurate. So there was a 23% increase in preoperative imaging diagnosis with 3D imaging. That's a significant increase in patients going to surgery.

One of the issues has been that the quality of 3D imaging for the last 15 years has been variable in its implementation. There was an article on pancreatic cancer in Radiology a couple years ago from a group at Duke. They looked at axial images and then filmed 12 or 16 3D images. They found that the 3D images didn't add anything and they couldn't read them as well. But you have to look at what they did: they were shaded-surface images. The data sets were 3 years old, so they were all from single-detector scanners and the radiologists had <1 month of experience. So the conclusion was that if you don't know what you're doing, you get bad results.

ZINREICH: In neuroradiology, 3D imaging is critical; it's like the essay. That is the only way the referring physicians will accept that particular data, because that is the only data that they can truly feel familiar with. We also have to realize that we have to do 3D images, because if we don't do them, somebody else will. So we'd better learn to do it, and do it fast.

NAIDICH: I think one of the problems with asking whether CTA is clinically effective or not is that we're looking at this issue too closely. In fact, we will need to depend on the whole armamentarium of imaging tools to assess these huge volumes. CTA is only going to be one component of a lot of approaches that will be intermixed. So it may be that an individual case needs to have CTA performed; perhaps it requires volume rendering; or perhaps a CAD application will need to be utilized initially. Imagine an environment, ultimately, in which you will have access to all these different tools simultaneously. CTA will only be one component of the whole approach of how to investigate data sets that are up to a 1000 images now, or even potentially much greater. Even though this forum is focused on CTA, I don't think we should look at it as a totally separate phenomenon. It should be part of a more global approach to how we will think about data management and data interpretation. It's just one tool amongst others. Ultimately, it will have to be integrated into a PACS. If all necessary tools are not somehow in one place at one time, we will never break the CTA sound barrier.

FISHMAN: I believe that at the 2003 RSNA meeting, both GE and Siemens will have 3D on the PACS. Basically, it's impossible to have all these separate imaging systems: 1) we can't afford them; 2) even if you can afford them, you don't have enough desk space; and 3) even if you had enough desk space, you don't have the time to keep going back and forth. It's kind of silly; it's poor management. Part of the problem is that we've done CT for 25 years, and we always did it in a slice-based environment. If CT started at 16-slice scanners and the rest didn't exist, and you started today, there never would be a question. No one would ever think of looking at axial images, that would be the dumbest idea you ever heard.

NAIDICH: That's akin to the idea that if someone initially started with CT as the first imaging modality, and only subsequently developed a chest X-ray, the chest X-ray would be considered an improved solution to the problem of a global assessment of lung disease.

FISHMAN: That also applies to the fact that if PACS was always there, and someone invented film, it would be incredible.

There is no better time than now to do CTA. Take some time and make some effort to plan, in choosing the contrast agent and concentration, and the timing. Take the time to actually learn how to do the tests, the bolus tracking, and the postprocessing. You have to learn each of those steps; if any of them fails, you are not going to be very successful. But I think for good patient care, it's not an option.

This is the important thing that people may forget: as radiologists, we always promise that we control radiology, because we can deliver the best care. But I think if you are not doing CTA, you are not doing the best care. At the SIR meeting last year, the president of SIR noted in his address that 80% to 90% of all diagnostic angiograms are history because of CTA and MRA. He said, If you're still doing it, just get over it. You can't be doing it. And if you are doing it, you are doing bad patient care.

SIEGEL: You've asked about selling CTA to the clinicians, and you made a point about CTA and pancreatic cancer. I think one of the important things is to prove that it works. You've shown how it does today, but the first time we've heard anything about numbers is this 70% to 90%.

ZINREICH: If you look at the proceedings today, we've had 4 hours of discussion, primarily technical. Some very critical points were made. But the next point, the bread and butter for the general radiologist, is going to be: now how am I going to do this in stroke? How am I going to do this in aneurysms? How am I going to do this in the tibial artery? How ever am I going to approach it? What am I going to do with the liver? They need specific points on how to do it.

SIEGEL: And when to do it.

FISHMAN: We talked about CTA today, and we didn't address the kidney or the pancreas. There are other topics we obviously didn't do. One thing that people will be interested in, after they get the core information we presented today, is: How can they do it in practice? How exactly do you do it? How do you get trained on it? People sit at lectures and hear us all speak about CTA. Everyone will listen to it, but then they'll go home and do the same thing they did before, as always. I think there is a gap. People are now able to say CTA is really good, and those images are really cool. But they will have 12 excuses why they can't do it themselves. They're too busy, they don't have time to learn, they don't know where to learn, they haven't been trained, etc.

I always ask a question of audiences: how many people feel they are comfortable with their workstation and with using it. Nearly always, 1 person in 100 raises their hand, so 99 are uncomfortable. So, can we tell people how to go from this point? We can provide protocols, but that doesn't make anyone do the process. So maybe we need to address workflow; how people can really do it. I think that would be a very important point to people: how to manage workflow issues.

NAIDICH: But, we have avoided another issue, another crucial step toward gaining acceptance of CTA. At some point, we must have the data that shows that CTA is really clinically effective. To do this will require that radiogists relearn both basic anatomy and newer clinical concepts relating to vascular disease. If you went into the general radiographic community and asked them to interpret some of the images that we've seen today, they would be somewhat at a loss. One of the great things about CT when it was first introduced was the decreased dependance on learning angiographic anatomy. Now, suddenly, you have to relearn anatomy again! One of the most important steps toward general acceptance of CTA will be the need to retrain radiologists about radiology.

FOLEY: I think that is a very good point. With all the vascular studies we are doing, many of us were not really trained in angiography. Now, they train radiologists in angiography early; I do the lectures and have kept that angiographic focus. But general radiologists may be uncomfortable discussing the issues related to aortic surgery or aortic intervention. But they can relate to the image, and discuss that one-on-one with the vascular surgeons. His angiographer would not have a problem doing it, but his angiographer is not doing the diagnostic angiography now­­the general radiologist is. So that's where the retraining issue is.

FISHMAN: So, if you were going to do specific topics for another meeting, it might a good idea to have a clinician there. What does the vascular surgeon want to know from CTA? Even things like vessels, as David mentioned. I haven't looked at vessels beneath the knee. I know there's a bunch of vessels that go there, but who knows what they are? Our RSNA exhibits this year are on vascular anatomy. We have a medical artist drawing the pictures, and it's interactive, and I think that might not be a bad thing. When we were all residents 1000 years ago, Kodak used to give out materials showing all those vessels. They were very popular, and I still have them.

SAINI: I still have them, too.

FISHMAN: That was the only material you ever had like that. Things like that might not be very hard to reproduce for current radiologists and residents.

NAIDICH: Well, I also think the manufacturers of contrast agents should be very much involved in popularizing and teaching these issues.

SAINI: I want to bring up one point we haven't discussed yet. We realize that money makes the world go around. So, one thing radiologists might think about is how they get paid for the CTA studies. If you bill a CTA examination as an abdomen/pelvic CT, then not only is it a noncompliant code, but it is less reimbursement on the professional side. So, radiologists also need some education regarding how to appropriately bill for these studies.

FISHMAN: Radiology is a very big job, including getting reimbursements for CTA. Because some people didn't properly organize, they did it really poorly. Gordon Harris, PhD, at Mass General went to HCFA and everything else, and we got reimbursement straightened out a bit better; but it's still lousy, I think. The trick is, you've got to know how to bill, so you can get paid well. It often doesn't pay to bill the CTA codes--if you use an abdomen and a postprocessing code, you do a lot better. But that's probably not an unreasonable thing. This is all part of the workflow issue. How do you build CTA into your practice and make it successful?

FOLEY: Contrast media injectors and CTA equipment don't even talk to each other. I now understand, from the GE side, that they are beginning to think about integration. I suspect it is the same with the other companies. From the point-of-view of the technologist who is implementing the procedure, that would make it easier for them.

FISHMAN: I think both GE and Siemens have worked on that. The issue that always slows it down is the liability issue; it's not a technical issue, quite frankly, it's purely liability. If they want to implement it, it's pretty easy to implement within reason. It's just that it's been that way for 10 years already.

I'd like to thank everybody for your excellent participation. I can say that I probably learned a lot more than I contributed. For the general population who will read these presentations and discussions, I think the one conclusion we can make is that, for all of us who are doing a lot of CTA, the process is still continually growing and changing. We can also thank Amersham Health and Applied Radiology for putting this meeting together so we could have this discussion. I believe we'll have some good materials and really important information for the radiology public.