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How to Integrate PET MPI as Part of a Multimodalit ...
How to Integrate PET MPI as Part of a Multimodalit ...
How to Integrate PET MPI as Part of a Multimodality Imaging Program
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Hi, my name is Ron Blankstein, and for the next talk, I will discuss how to integrate PET as part of a multimodality imaging program. During this talk, I will discuss the complementary value of PET with coronary CT and geography. I will discuss how we apply FDG imaging in addition to the typical coronary PET indications. I'll also mention some factors that are useful when deciding between PET and other types of stress tests. So the complementary value of PET and coronary CTA is probably well familiar to any of you who do multimodality imaging. In fact, 15 to 20 years ago, we used to think that maybe in the future, we will do both PET and coronary CTA, and we would combine those tests, and while that was something that technically was, I think, exciting, we very soon realized that it is very rare for a patient to truly require both tests. So today, the model is that we should select the best initial test, whether that is a PET, a coronary CTA, or perhaps another imaging test, and then we only would perform the second test when required. So for example, we can start with a PET, and most of the time, we would have diagnostic information, and we will answer all the questions that are needed, but at times, we may decide to do a coronary CTA after a PET. On the same way, we can also start with a coronary CTA, and only if needed, we can then perform another test, which is a PET. So I guess with this construct in mind, the questions that come to mind is, when is coronary CTA helpful after a PET, and conversely, when is PET helpful after a coronary CTA? So let's go through some examples. When is coronary CTA helpful after a PET? First of all, if the PET results are inconclusive, that certainly can happen sometimes if there's artifacts, perhaps if the myocardial blood flow reserve information is in a range where it's unclear if it really represents abnormal disease or maybe just diffuse atherosclerosis. Those would be examples of inconclusive PET results. But also when there's actual evidence of ischemia in PET imaging, but we may be uncertain, is it a really three-vessel disease or left-main disease, and maybe we want to rule out high-risk anatomy. So here's an example. This is a PET study right here, and this particular example, there's ischemia in the inferior wall. There is actually a severe defect that is reversible involving the inferior wall, part of the infraceptor wall. We can see this also on the vertical long axis on the bottom of the slide here, a severe defect involving the entire inferior wall. So when you see a study like this, you may say, well, there likely will be a high-grade obstructive disease in the right coronary artery, and of course, if you prefer to look at the bullseye, here's the bullseye showing also severe ischemia in the RCA. But one of the important things to consider here is also the myocardial blood flow reserve, which in this case was most impaired in the distribution of the RCA, but it was also impaired in the LAD and the left circumflex. So in this case, we decided to do a coronary CTA to better identify the anatomy. Perhaps no surprise, but we see a high-grade stenosis in the RCA. This is a lesion that now that we see this, we know this would be relatively easy to intervene upon. It's a very focal lesion. This is not a chronic total occlusion. That might be a more difficult intervention. But when we do a coronary CTA in this case, we can also see that the LAD and left circumflex are both completely pained. Yes, there are coronary calcifications. There's mild stenosis, but no flow-limiting or no obstructive disease, I should mention, either in the left circumflex or the LAD, corresponding to the fact that there's also no evidence of focal ischemia. So when we combine the information here, we can see that there's flow-limiting disease in the RCA responsible for the severe ischemia. There's also atherosclerosis in the LAD and left circumflex. And while that atherosclerosis is responsible for some reduction in myocardial blood flow reserve in the LAD, where the blood flow reserve is 1.31, and in the left circumflex where it's 1.59, there's also a reduction in myocardial blood flow reserve. But this is non-obstructive disease. Another example where we may want to perform a coronary CTA after PET is if we suspect microvascular disease. The important thing to know is that when we suspect microvascular disease, we always have to rule out obstructive disease. So on this slide here, I wanted to discuss two conditions that we summarized in the chest pain guideline on the left, coronary microvascular dysfunction, on the right, ischemia without obstructive coronary disease or ANOCA. One of the very important concepts is to make either one of these diagnoses, it is very important to rule out obstructive disease. The coronary microvascular dysfunction is dysfunction of the microcirculation, which impairs blood flow reserve. This is a condition that we may want to diagnose when patients have persistent anginal symptoms. Some of the factors that increase the likelihood of coronary microvascular dysfunction includes risk factors such as diabetes and hypertension, but also abnormalities in the ventricles such as left ventricular hypertrophy or an infiltrate of heart disease in the myocardium. We may also suspect this when we see small coronary vessel size or on small lumen volume. So coronary microvascular dysfunction, really the role of coronary CTA here is to rule out obstructive disease. The role of PET is to perform quantitative myocardial blood flow reserve and identify that that's abnormal. This is different but can overlap with ANOCA, which is ischemia in the absence of obstructive coronary disease, or we now could see evidence of focal ischemia in patients who have diffuse atherosclerosis. Let's switch gears and now talk about when is PET helpful after a coronary CTA angiogram. So first, if the coronary CTA results are inconclusive, this is of course can happen if there are extensive calcifications and it's difficult to evaluate the lumen. It can happen, of course, if there's artifacts from coronary CTA that rendered the images inconclusive. Another example when we may want to perform a PET is when there is actual obstructive coronary disease but we are uncertain if there is ischemia or perhaps the amount of ischemia. This is most common when there is moderate stenosis. So as an example on this slide here, we can see a moderate stenosis in the RCA in one patient or another patient that has moderate stenosis of the LAD. In both of these cases, it's unclear if these are flow-limiting lesions. One technique that you can perform in this case is an FFRCT if this was a focal lesion and if that technique is available, you can of course do many other types of stress tests but a PET would be also a very good choice to perform if you're uncertain if there's a flow-limiting disease. I think PET would be even more preferred if there is extensive atherosclerosis in multiple lesions or image quality by CT, which is not very good, for example, for conditions like FFRCT. So PET would be an option here. Another example is when patients have extensive non-obstructive disease and it is unclear if there is ischemia contributing to their symptoms. Here's an example and this is a 72-year-old female with hypertension, obesity, and dyslipidemia. She was referred for intermittent chest discomfort. She actually had in Agatson a score of 614, so she has a severe amount of calcified coronary plaque. She also had a coronary CT at some point showing non-obstructive disease as well, but the question in this case is, is the atherosclerosis here, is her calcium score or the plaque that she have in her arteries responsible for her symptoms? So in a patient like this that has a severe amount of plaque, what would be the best type of stress test to perform? Certainly you can perform an exercise treadmill test. I don't think that's unreasonable in this case. If she has good exercise capacity and no symptoms, that might be reassuring. SPECT is an option, but I think PET is a far better option, especially in a patient who has severe calcifications where we might be concerned about multivessel disease, which PET can diagnose, and SPECT is going to be much more limited for diagnosing multivessel disease. Coronary CTA, if you only knew about the coronary calcifications here, is an option, but with a calcium score of 614, I think not all CT scanners are going to provide adequate image quality. So if you have, for example, a photon-counting CT or a contemporary high-quality CT, you may be able to have diagnostic images with this calcium score. If you have an older generation, 64-slice CT, perhaps coronary CTA might not be the best option because of the focal dense calcifications that we can see here in the LED. Active angiography is pretty much not going to be a good test here, not endorsed by our guidelines for a patient who has stable symptoms. So in this particular patient, a PET was performed. There's no evidence of ischemia when we look at the perfusion images. If we look at the myocardial blood flow reserve, we can see that the blood flow reserve is greater than 2 in all coronary distributions, so the normal myocardial blood flow reserve excludes severe multivessel stenosis or microvascular disease, and that's associated with a very favorable prognosis, even in this patient that has a severe amount of coronary calcifications. The other condition where PET is helpful after coronary CTA is when we suspect microvascular disease. We discussed this already a few slides ago, but importantly, this is a condition that requires us to rule out obstructive coronary disease, and I would state that most patients who have microvascular disease also have epicardial coronary atherosclerosis. It's the majority of cases that microvascular disease is associated with plaque in the coronary arteries, but every once in a while, we would see a case like this where a patient has a PET. There's no focal perfusion defect. We see here a reduction in both myocardial blood flow during stress and also myocardial blood flow reserve, that the normal for us in this patient would be more than 2, and we can see that globally, the blood flow reserve is reduced everywhere, with an average of about 1.4. And interestingly, in the coronary CTA performed in this patient, we can see in the LAD, in the CERC, in the RCA, no evidence of plaque at all, so this is an example of a patient that has microvascular disease despite no epicardial disease. This is actually a fairly rare entity. Usually when we see this, these are patients who have underlying myocardial disease as well, for example, left ventricular hypertrophy or infiltrative disease such as amyloid. I'm just going to mention, even though this is really not the focus of our talk or of our imaging series here, that aside from looking at perfusion, there's other clinical uses of PET, and specifically when we do FDG imaging, this is now not for the coronary arteries, but we use this to diagnose inflammation, infection, or viability. So as an example, the infection here is a patient with a mechanical aortic valve and has on CT a pseudoaneurysm of the ascending aorta. When we see a pseudoaneurysm like this, this is actually a contained rupture. One of the questions might be, is this infected or is this maybe a chronic complication? And we can see that there was actual FDG uptake in this area supporting the fact that, in this case, this was an inactive infection. We can also see infection not just in mechanical valves, but also when patients have implantable devices such as pacemakers or defibrillators, and this is a factor that can be used when deciding whether there's evidence of endocarditis. Importantly, these are infections that you're not going to be able to diagnose as echocardiography. CT also not all that helpful for devices, so FDG has a very unique role for device-related infections. At times, we can also use imaging to follow response to therapy. This is a 25-year-old male with congenital heart disease who has FDG uptake of a stent in the descending aorta, as you can see on the baseline images here. Two weeks later, that activity goes down, and two months later, no further activity in that stent showing appropriate response to antibiotic therapy. Another way that we use FDG imaging is to look for inflammation in the myocardium, and the most common disease for that is cardiac sarcoidosis, where the typical example on imaging would be a perfusion metabolism mismatch, where there's increased FDG corresponding to a perfusion defect in the absence of coronary disease, because we always want to make sure this is not hibernating myocardium, but in the absence of known coronary disease, in the correct clinical context, this can help us diagnose cardiac sarcoidosis, and even more so when we can combine it with cardiac MRI. So going back to perfusion imaging for coronary disease, I'll just end with the important question, which is, how do we choose between coronary CTA and stress testing? This is, of course, a topic that we addressed in the ACC chest pain guideline, and as you can see on this slide here, for patients who have an intermediate to high pretest probability of obstructive disease, coronary CTA or stress testing, including PET, all have class 1 indications. The guidelines suggested, and these are not formal indications, but just recommendations in the text, that generally in patients not on optimal preventive therapies who are younger, the coronary CTA may be preferred, while in individuals who are older, who have a higher likelihood of ischemia, stress testing would be preferred. I personally think that age is not that important of a construct here anymore, especially as CT scanners get better, and perhaps coronary calcifications are really less of an issue with newer generation coronary CTA scanners, especially photon counting CT. On the other end of the spectrum, there could be younger individuals who have significant ischemia and whom stress testing might be the best approach. So I would actually encourage individuals not to focus too much on age. I think this has gotten a lot of attention, I think, since the guidelines were published. But more importantly, focus really on the objective of testing. So we would favor CT if our objective is to rule out obstructive disease or to identify non-obstructive disease. On the other hand, we would favor stress testing if we want to perform ischemia-guided management. What does that mean? That means that we want to quantify how much ischemia there is, and the more ischemia there is, the more benefit there may be for revascularization, or at least in telling us that patient symptoms are actually due to ischemia, which is not always straightforward in all clinical cases. If a patient previously had a functional study that's inconclusive, coronary CTA might be the best test to do this time around. And conversely, if a CTA was inconclusive, a functional study would be helpful. Of course, if you have to do a stress test, of all the different stress tests, I do think PET offers many advantages, and it is the most robust stress test that we have available. So of course, throughout these lecture series, we talked about the many advantages of PET over SPECT, but PET really has many, many advantages. So if a stress test approach is preferred, PET is a very, very robust approach. And as we discussed a few slides ago, one of the advantages of PET is also the ability to diagnose microvascular dysfunction. Again, remember, you have to rule out obstructive disease. You have to do quantitative blood flow to show that the blood flow reserve is abnormal, but that's how you would make that diagnosis of microvascular dysfunction, or CMD. So here is a few take-home points. First, test selection depends on availability and expertise. I think this is true of all modalities, and it's not just the availability today. It's also the technology. This is especially true for coronary CTA. A newer generation of scanners are going to perform much better than older generations, but this is also true of PET having the right technology, having the right expertise, for example, to know how to do myocardial blood flow reserve. In selected cases, integrating data from both PET and coronary CTA offers complementary value, and I state this in selected cases because the majority of patients will only need one or the other, not both tests, and we talked about examples when a CTA might be helpful after a PET and vice versa. PET may be the most helpful test in symptomatic patients with known coronary disease or when there is clinical suspicion for coronary microvascular dysfunction or ANOCA, ischemia, in the absence of obstructive coronary artery disease. On the other hand, CTA may be helpful after a PET to rule out high-risk anatomy or if identifying the amount of underlying atherosclerosis would influence either pharmacologic or preventive therapies. With that, thank you all.
Video Summary
Ron Blankstein's talk focuses on integrating PET (Positron Emission Tomography) with coronary CTA (Computed Tomography Angiography) in multimodality imaging programs. He discusses how PET complements CTA, especially when images are inconclusive or where detailed vascular assessment is required. Blankstein emphasizes selecting the best initial test, like PET or CTA, and proceeding with an additional test only if necessary. PET is advantageous for quantifying ischemia and identifying microvascular dysfunction. Meanwhile, CTA effectively rules out obstructive disease and assesses atherosclerosis' extent, crucial for managing patient symptoms and planning therapeutic interventions. The importance of technology and expertise in using these imaging modalities is underscored, highlighting advanced newer generation CT scanners. Each method's selection depends on the clinical objectives and patient circumstances, particularly for determining the risk of coronary microvascular disease or when known coronary disease symptoms persist.
Keywords
PET
coronary CTA
multimodality imaging
ischemia quantification
microvascular dysfunction
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