Chapters Transcript Video Advances in Stress Testing/NI Imaging Dr. Sanjay Shah gives an overview of cardiac PET imaging and emerging clinical applications. Cardiac pat imaging is my topic. We know we don't have the Pat imaging yet at Santara, but it's in horizon and it's a good idea to start discussion and generate the interest for the guys to get more educated and have the interest. So we'll start with. And I would just like, I don't have any conflict of interest for this talk. And I just like to get the acknowledgement that the ethnic website, American Society of Nuclear Cardiology has great resources for the pet imaging, how to start a program and how to get ready for the pet. And Dr Dennis Calnan has a great presentation there and some of the content was borrowed from the ethnic website. So I'll start with a case here for many of the clinicians we face this commonly 75 year old as symptomatic female with hypertension diabetes, high risk patients comes for the pre operative prior to the elective hip replacement and she undergoes the ph pharmacological pat with the rubidium. And these are the images, I don't know how well you can see it there from distance. So I'll just help it out here that OK, just go back. So there is kind of a small area of CAL and digital interior reversible defect without transient ischemic dilatation. So my question is we face this all the time in the real world. What would you do? You say it's a normal scan? It's not a normal scan, I would say. So basically, between B and CB is a high risk scan, you want to consider cat C am ischemia, low risk scan, no discrimination and let her go for surgery. So again, it's a dilemma. You can have a reasonable argument both ways of B and C. Some people may offer the cat. Some people say, OK, it's a low risk patient is asymptomatic. I would let her go for surgery. So, but if I cannot add the fourth option here saying that how about more relevant data, then I think everybody would say, yeah, let's go for the more relevant data that we can get it from the pad compared to the spect imaging that it gives you the only related perfusion. So next slide, what we have is my blood flow and blood flow of information that we get it from the pad. So the resting, this is the resting blood flow, um resting blood flow normal is about 0.4 to 1.2 ml per gram per minute. So that resting blood flow is normal. And uh this is the stress and uh this is the myocardial blood flow reserve. So the way the myocardial blood flow reserve is calculated is um dividing the stress blood flow divided by the wrist and normal should be about two and abnormal, considered less than 1.7. So this patient has definitely abnormal myocardial blood for reserve and patient under when cardiac and patient had a lap main disease as well as complete occlusion of the RCA. So that's kind of the strength of the pat compared to the just packed images, which only looks at the relative perfusion among the segments and it gives the additional. So the purpose I just wanted to start the discussion here to see kind of what the PAT will bring it out in addition to the spec. So some of the references you'll hear in relation to the spec and what are the data out there for the diagnostic and the prognostic value? And how does it help you manage the cases? So this is just kind of very superficial touch into the nuclear physics. What is Pat Positron emitter tomography? And basically the radiole type pat, keep going that emit the positron, positron is the animator of the electron. And once the nucleus come up, positron is emitted, it travels to some degree and then it meets the electron and both opposite. So it results into inhalation event and both disappear and results into the 5 11 KV photon in the opposite direction. So just kind of this number, this energy of the photon is much higher compared to the spec tracers that we use for the thallium, it is about 68 to 80 KV. And for the technician is around 140 so more energy and less, less attenuation. So that's one other thing and also 280 degree. So that leaves the current coincidence, we call it, the photons are registered at the same time in the detector. The other thing that you want to pay attention that we look at it is the deposit on how much it travels before the inhalation happens. So the longer the distance, this is the point where the camera is going to detect that the nucleus is here versus the actual position is here. So the more the range the car, the more likely to have the scatter. So the less the range you have a better resolution images. And this is kind of just the schematic of the camera, the detectors are positioned in the kind of circular ring and then it can detect the photons 180 degree rather than coming at one isolated photon. So it has a better detection. And basically comparing to the spec camera, they don't move the patient is there in the center and is constantly registering the events, coincident events we call it there are millions of counts. So there is very good temporal and spatial resolution with the pet images compared to the spec. So just also kind of brief touch about the comparison between the spec and the pet tracers that we use on the bottom, we have 99 technician system maybe. So if you look at the half life is six hours and is delivered by the pharmacy radio pharmacy and then the extraction is relatively low even where they're high flow. And if you look at the milli verse, that is very high around nine, if you look at the pet tracers, rubidium, 75 seconds, half life and then the range was 8.6. Versus if you look at ammonia, 10 minute half life. And the positron range is 2.5 so much better, less scatter and less attenuation and better resolution. And in the next slide, I'll just show that the tracer K takes a little bit better. But Rubidium you need generator and I'll show you the picture of that. And for the N 30 pneumonia, you need to have the onset cyclotron. Same thing with the 50 no water as well as 18 flu pres which is not approved yet. So this is the tracer kinetics that you see. The ideal on the X axis is the absolute myocardial blood flow. And on this y axis is the my uptake, the ideal tracer should have, should have the 1 to 1 relationship. The more the flow is tracer uptake is exactly the proportion that will be the ideal that comes close to the 50 no water. If you look at the 99 M technician sister B as you increase the blood flow from 1 to 3 relative, my uptake is relatively blunted. And as you go higher up, it becomes more plateau 18 82 rubidium is better than technetium ammonia is even better. So you have a better, you can differentiate the myocardial blood flow better based on the uptake of the difference of the tracer. And this is just one of the schematic of the rubidium generator. And this is this is the core from the 82 strontium. It is iu rubidium illiterate and then kind of infused and everything is kind of packaged into this generator. And this is the cyclotron, they used to become much bigger and with the advances in technology, they are getting more and more compact and a little bit more better wider spread use. This is the Tics ion 12 C that we are kind of hoping to get. And the protocol is also very efficient. You get a baseline baseline positioning as well as the calcium score if you want and then ammonia is infused. Basically it's about seven minute scan and then immediately come up within short time, the stress and you can get the stress images attenuation correction. Also images you can get with the both and then whole protocol could be based on the timing, it could be 30 35 minutes and very efficient use and look at the radiation exposure is 2.1 milli very low radiation exposure So we'll talk about some of the strength of the cardiac pad. Diagnostic accuracy is higher image quality is excellent protocol is very efficient, very low radiation exposure. And then additionally, some of the information we get is the peak and the wrist, we can get the ejection fraction. If you look at the spec, the ejection fraction is obtained when the images up in 30 to 40 minutes or whatever the timeframe afterwards. So it's not really the peak stress ejection fraction that you are getting with the specced versus with the pad, you can get real time as the infusion goes on with the kinetics and the software, you can get the myocardial blood flow as well as resting and the peak ejection fraction. And I'll show you the data about increasing the ejection fraction and ejection fraction reserve having prognostic value. So this is the diagnostic accuracy. If you look at here, this was pat was compared with the other remaining modalities. And the base standard was the cardiac cath with ther and the pat came out much ahead of 85 per cent accuracy. The sensitivities here and the specificities on these axis. So the pet performed really well in terms of the diagnostic accuracy. So we talked about the attenuation correction is great. Scatter correction is very robust. Spatial resolution is much better, better compared with the ammonia compared to the rubidium uptake is much higher proportional to the myocardial blood flow. And the timing is also very efficient protocols. So this is the mentioning the same data. So this is just kind of example of the rubidium study. If you look at it, uh keep that. So in spite of the increased diaphragmatic uptake here, if you can see the inferior wall is still very well defined. And some of us who read kind of the spec studies would have struggled here with the kind of the image interpretation of the inferior wall. So attenuation correction is very robust. If you look at the images, the border and the LV differentiation is very well. And the same thing here with the ammonia, the resolution is so good that you can even see the papillary muscle in some of the studies here. This is again, talk about the radiation doses with the PAT. It's less than nine milli American Society of Nuclear Cardiology had a position paper that the labs should strive to get the radiation exposure less than nine milli as much as possible and very hard to get it with the spa. But with the PAT, it is possible and look here what we used to use before dual isotope a long time ago that we don't use it anymore. So in addition to the myocardial blood flow and blood flow reserve, we also have the LVEF reserve, we call it. So this is the paper from Dr Darla. It showed that with the vasodilator stress in a normal person with the low likelihood of coronary disease, the injection fraction does go up with the post stress compared to the wrist. And as the geographical disease score goes higher, the rise in the ejection fraction gets blunted or even gets negative ejection fraction drops. So LV, ejection fraction reserve is one of the prognostic indicators. It mainly kind of helps. It has a very great negative predictive value that you have normal LVF reserve greater than five per cent. It has a 97 per cent negative predictive value for excluding significant three vasal disease or left main disease. And another important feature that more and more attention is being paid to the microcirculation. And so myocardial blood for reserve not only looks at the macro circulation but also at the microcirculation. So we encounter many patients who have the chest pain and their end geographically coronary disease. We don't see much or some diffused disease. So my blood flow reserve would estimate not only the macro circulation but also the microcirculation. And again, this is the formula for the flow reserve peak, my blood flow divided by the rest. And this is again the slide showing the very high negative predictive value more than 97 per cent for the reserve to exclude the high risk coronary artery disease. This is another paper from Dr Patel in 2020. So this was in general population and basically on the x axis is the time frame and this is the basically the disease event rate and what it shows that the higher the ischemia, we all know that the prognosis gets worse. But even among those sub groups who had no ischemia, mild ischemia or or severe ischemia, on top of that myocardial blood flow reserve had additional prognostic value for the time plotted versus the survival. So it does has a prognostic value among multiple sub groups of the coronary arty disease. And it also helps guiding the management. So here is the myocardial blood flow reserve as it gets worse. And this is the risk of cardiovascular events and the death and the medical treatment versus early revascularization. So, cut up point of 1.8 is shown that the early re vascularization leads to the better outcome on those patients compared to medical treatment they got. All right. Ok. So basically, it just come up, it just shows that the prognostic value of the pet in terms of diagnosis and help in the treatment and vascularization. And it has some kind of emerging other applications also which include viability, sarco doses as well as a prosthetic device, infection and other kind of emerging prognostic in ST as Dr initially, Mora mentioned, there are a lot of research going on about identifying the high risk patients. So thank you for your attention. Published October 17, 2023 Created by Related Presenters Sanjay G. Shah, M.D. Sentara Cardiology Specialists View full profile
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