All right, in this presentation, we are going to talk about incidental findings on the CT scan in a PET CT study. Here are my conflicts of interest, potential ones. I don't believe any of them are relevant to this presentation. So as you know, all PET image data needs to be attenuation corrected. It can be attenuation corrected with a dedicated scanner or with a hybrid PET CT device. Both of these will work well. With the dedicated camera, we will routinely have spatially relative perfusion defect identification. We will have some methods of quantification. We can quantify flow. We can look at rest and peak stress, regional wall motion, thickening, and ejection fraction. And of course, with hybrid PET CT, we get the same parameters, but the devices are newer. The electronics are such that there's higher count sensitivity, there's higher resolution, there's better signal to noise, and because of being able to use lower dosages of tracer, the radiation exposure is lower. We can also routinely with PET CT recognize the presence of coronary calcium, and we have learned the importance of recognizing that a patient has subclinical coronary disease. In the case of somebody with a normal scan, it can make a big difference in terms of educating the patient and treating the patient for risk factors and so forth. If one wants to perform cardiac sarcoid, or device infection, or valve infection type studies, clearly CT will be necessary and very helpful. And finally, the CT component can be used for independent coronary and vascular CTA and EP studies and so forth. So there are a lot of advantages in making that transition from dedicated PET to PET CT. Obviously, there are also challenges. It's going to require a larger space, greater expense, shielding, and it's heavier. Somebody is going to have to be level three trained because there are safety issues. The camera settings become important in terms of tube current and voltage in the field of view. Hospital policies will need to be looked at in terms of privileging and risk management issues. If it's in a medical office, they may have policies as well. Finally, state regulations will need to be considered with respect to whatever laws might be in existence relative to physicians performing and interpreting CT data and technologists. How to address the CT scans is a standalone issue, and that's what we're going to talk about now. So I want you to remember a few things about handling the CT data in a PET CT study, a cardiac PET CT study. First of all, these are non-standard scans. We're only imaging a part of the chest. The slice thickness is different than would be if one was acquiring a chest CT, for example. If one is doing this for only attenuation correction purposes, the image quality is very low resolution, and it's poor quality, frankly. It's adequate sometimes to make a diagnosis, but it certainly is not precise. Currently, there are no rules or even recommendations about how to handle the CT data. That may change, but right now it's more or less cowboy country. The prevailing practice is to inspect the scans, to report pertinent abnormal findings, and to retain in storage the CT images. We and many others incorporate a disclaimer statement, given the fact that these are non-standard scans and we're only imaging a portion of the chest. In the case of a coronary calcium scan, we say this is a limited CT scan of the chest for evaluation of coronary calcium only, and is not intended for any other purpose. In the case of an attenuation corrected only scan, we would say this is a low resolution, non-diagnostic CT scan of the chest for attenuation correction, and is not intended for any other purpose. There are several options. One is to interpret these scans independently, that is to learn how to do it. I'm going to take that position, because we've done that at our place for the last 20 some years. If you are a level three trained in CT, as everybody at our place is, who looks at these scans, who is on the nuclear rotation, you will have had appropriate training and exposure in order to be able to interpret the CT component. Several findings are common. They're part of the evaluation process of the examination of the CBCCT, and so if you are a level three trained, you should be able to do this independently. In some settings, you can co-interpret with a radiologist. In other settings, you can have scans overread by a radiologist, with the radiologist being somewhere else, and therefore two reports get generated. One that's focused on the perfusion, and one that's focused on the CT. In those settings, a radiologist might overread everything, or might only overread selected ones. In other words, I've looked at it, and I found something, and I don't know what it is, and I want the radiologist to take a look at it. That would be an example, or as I said, you don't necessarily have to have a radiologist look at any of them, and I'm going to take that position as I work my way through this today. There are two distinct types of CT scans that are commonly acquired as part of a PET-CT MPI study. One is to quantify coronary calcium. That's a higher resolution scan, it's performed with ECG gating, and it is going to expose the patient to one to one and a half millisievers of radiation. If it's done only to perform attenuation correction, the tube current and voltage will be turned down because it doesn't have to be a high resolution study. It does not have to be ECG gated, and the patient should be getting an exposure somewhere of 0.1 to 0.2 millisieverts of radiation, so it's much lower. The first step is to get a positioning scan. We call this a topogram in our place. The area of interest will extend from this level here, from where the trachea divides, down to below the heart. That's the area of interest that we want to image. We look at the topogram all the time, however, because we are only imaging a portion of the chest, and yet we have taken this topogram, and what if there is pathology outside of the region that we are subsequently going to be looking at? Here's a big mass in the right upper lobe, and it would be a shame to miss that. We always look at the topograms. There's a big difference in the way the images look if they are acquired in a high-resolution mode for quantifying coronary calcium and a low-resolution mode for attenuation correction. You can see that it's much more pixel-y on the low-resolution mode, but nonetheless, if you take a look at the aorta and the pulmonary artery and the descending thoracic aorta and so forth, you can appreciate that, yeah, there's information that makes it worthwhile, even with the low-resolution scan, to take a look at things. We're going to talk here about incidental findings. What do you want to look at? Well, you want to look at cardiovascular things for sure, and you want to look at non-cardiovascular things. So, the aorta, pulmonary artery, valves, chamber sizes, pericardium, coronary origins, you're going to want to look at all that, and non-cardiovascular, the esophagus, portions of the liver, portions of the lungs, portions of pleura, portions of mediastinum, breasts, ribs, and spine. Those are things that you want to keep in mind, and remember, you're only looking for things that are abnormal. You put it into different window settings, depending on what you're looking at. These are usually automated, so you just push a button and it automatically goes into a mediastinal or soft tissue window, if you're looking for cardiac structures, liver, mediastinum, or breasts, a lung window for the lungs, and a bone window for the bones. So the way we do it is we do it as a kind of a movie. This is a mediastinal window, and it's starting at the bifurcation of the trachea, and we're imaging down, all the way down, and then all the way back up. Now, what we tend to do is we look at the cardiac structures and the other things that I mentioned to you before. In this case, there's a very, very large hiatal hernia. We can see a little bit of calcium in the coronary arteries. We can see the size of the aorta and so forth. And then we put it into a lung window, and now we're focusing on just the lungs. The way we like to do it is we look at the right upper quadrant first, up and down, and then the right lower quadrant, up and down, and then the left upper and the left lower. And here, we're looking mainly for pathology in the lungs. We're looking for effusions, pneumonitis, nodules, cancers, and so forth. Okay, cardiovascular system. Let's just look at some common things that we will see. Obviously, calcium. Calcium, easy to recognize regardless of whether it's a low-resolution or high-resolution study. If it's low-resolution, we can at least classify it as small, moderate, or extensive. Valvular calcium, if it's a non-gated study, we have to give just a general description of it. If it's a gated study, it can be quantified. How much calcium is there in the aortic valve? That can be a number, and it's an important number in terms of how severe the aortic stenosis may be. Mitral annular calcium, pericardial calcium, effusions, the size of the ascending and descending thoracic aorta. Very easy measurement in cross-section. You can almost always see the coronary artery origins without contrast agents. And it's important to make sure the left main is coming off the left sinus and the right coronary is coming off the right coronary. And importantly, look at the size of the coronary sinus because if it's large, something is wrong and you need to think your way through what might that be. So here's coronary artery origins. You can see the left main is coming off the left sinus and you can see the right coronary is coming off appropriately from the right sinus of the cell. Almost always, you'll see that. Calcium, as I said, it jumps right out at you. Here's heavily calcified aortic valve. Here's some calcium in the mitral annulus. Here's some calcium in the right coronary artery. Very easy to recognize it. Here's some calcium within a myocardial infarction at the apex of the heart. Here's some in the lateral wall after myocardial infarction. So calcium, easy. Here's a large descending thoracic aorta. You got to worry about dissection in these cases because you can see that there is soft tissue outside of the wall of the descending thoracic aorta. Here's the case of a large coronary sinus. And you can actually be suspicious here of a left-sided SVC draining into the coronary sinus to explain what's going on. For this particular study, you won't see high enough up to be able to actually see the left-sided SVC except in cross-section here. But if you did image higher, obviously here's the contrast enhanced study and you can see it very easily up here. Mitral annular calcium, you'll see lots of that. Pericardial cysts, so these low attenuating cystic appearing smooth walled structures attached to the pericardium. In this study, there's multiple sites of calcification in the descending thoracic aorta in the coronary arteries in the mitral annulus. In this case, a large hiatal hernia again. Pericardial effusion can be differentiated from the higher Hounsfield units of the myocardium and of the blood pool. You'll notice that you can't tell the difference between myocardium and blood pool. They have, unless the patient is severely anemic, there's lots of iron in the blood pool and the Hounsfield or attenuation coefficients are about the same of myocardium and blood pool. This is just an example of a Watchman device sitting in the left atrial appendage. Going beyond the cardiovascular system, things that you will want to look for, first of all, the anterior mediastinum. Okay, there should be nothing but fat up here. So this is abnormal. This needs further investigation. So what are you going to do when as a cardiologist, for example, you look at the scan and you see there's something in the anterior mediastinum, it's only partially visualized. Basically, you're going to want to pursue this. Now, you can have a radiologist look at this with you, but almost certainly what's going to have to happen is another imaging study to figure out what's going on in the anterior mediastinum. You could ask for a full lung CT without contrast. That would be one approach because you're only seeing a portion of the lungs. Or you could say you would like to have a contrast-enhanced CTA to evaluate that. Or you might not want to mess with this at all except just to say there is something abnormal there and call the referring physician and let the referring physician make the recommendation as to whether to simply refer this patient on to another specialist or to order the test him or herself. Lung nodules, if they are six millimeter or more, they need further investigation. Again, you're only imaging a portion of the lungs. So if you see one of these at six millimeters or above, you're going to want to recommend a full lung CT. Again, you probably aren't going to order that yourself, but you're going to in your report, in your myocardial perfusion imaging report, you're going to say a six millimeter nodule was seen in the right lung, in the limited views of the right lung, recommend full lung CT. And certainly, you know, some of these, most of these are not going to be malignant, but occasionally they are, and you don't want to have missed that. Things like this, you don't have to get fancy about trying to interpret what you are seeing and know what this might or might not be. This is in the mediastinal window, this is in the lung window. It shouldn't be there, it's abnormal. So again, what are you going to do? Well, you're going to draw attention to the fact that there's an abnormal lesion in the right lung and recommend a full lung CT. Here's another example of a right lower lobe mass and probably malignant. Multiple ground glass opacities that you can see, these shouldn't be here, right? And they're easy to recognize in the lung window, and you've got to consider infection or malignancy, but again, it's not your job to try to sort all that out. It's just an abnormal finding, it needs to be pursued and recommend a full lung CT as a first step. This is just another, these are just other abnormalities that would be consistent with pneumonia, but you don't have to know that. You don't have to know what the differential diagnosis is, you just have to recognize that it shouldn't be there and further investigations are needed. And these are images of COVID, pertinent in today's era. You always want to look at these things as quickly as you can after an MPI is done with a CT, because if somebody has got active COVID, it's important to make sure that communication to that person is made as promptly as possible to limit further spread. Hematomas, this is, you can see there's a lesion here on the lung window, you can barely see it over here on the medial spinal window because the attenuation coefficient is so low. These are rounded, they're fatty, they're benign. You'll get used to seeing some of these, and they of course do not require further evaluation. Bilateral pleural effusions always need to be commented on. Here's a large left atrium. I don't actually measure the size of the cardiac chambers because in this case, it's a fairly low resolution scan. I don't know whether we're capturing it at end diastole or end systole. And if it is a gated scan, we capture it at end diastole in order to quantify coronary calcium. And of course, that's a different size than what people are used to looking at with echocardiography at a different time interval. So I don't measure them, I just say it's large. Esophageal problems, again, that's not normal. Everybody could recognize that. Here's in a coronal view, you can see how big that esophagus is, how it's ballooned out. We just have to say the esophagus looks horribly abnormal. Recommend a gastroenterology consult, and you're off the hook. It is important to look at breast tissue. This is a mass in the right breast of a lady. And usually you can look up on the record and find out if they've had a recent mammogram and if these things are known. If not, you would recommend mammography. You'll see a lot of hepatic steatosis. Important to comment on that. Again, it's not hard to recognize. We typically would compare the appearances of the liver to the spleen and measure with the region of interest what the Helmsfield unit is for the liver compared to the spleen. And if it's more than 10 units lower than the spleen, we would label the diagnosis of hepatic steatosis. You'll see lots of hepatic cysts. They're nice and smooth, low attenuating lesions, and very common, unimportant incidental finding. CITES, again, pretty easy to recognize. It is important to look at the ribs and to look at the spine. And again, you don't have to be a radiologist. You just have to force yourself to take a quick look and be sure that there's nothing that is horribly abnormal. In this case, clearly something is expanding within this rib. And the attention needs to be drawn to things like that. What is this? When I looked at this, I have no idea. I just know I have not seen something like the tissue here that seems to be wrapping around the descending thoracic aorta. This turned out to be a B-cell lymphoma. Again, just recognize the fact that something's not normal. I mentioned that sometimes you can actually diagnose anemia with this study. If the iron content in the blood is very low, there will be a difference between the attenuation coefficients of the blood pool and the myocardium. I don't know how well you can see that here. Usually when it gets down to about seven, it is easily recognized. And we make a diagnosis of anemia in symptomatic patients with dyspnea many times each year based on that. So I think my take home point here is remember, these are non-standard images. Some of them are very low resolution depending why you acquired the CT component. You're only seeing limited views of the lungs, limited views of the liver, and so forth. So describe what you see. You can recommend a full lung CT. You can recommend a pulmonary consult. You can recommend mammograms, et cetera, in your report. You don't have to be a radiologist in order to be able to handle the CT data in a hybrid PET-CT study. Thank you very much for your attention.

PET-CT

incidental findings

coronary calcium

attenuation correction

hybrid devices

abnormalities