 Hello everyone, I'm Dr. Shomali Khosh and I'm going to talk on imaging in COVID today. Now we all know that the principal diagnostic test is RT-PCR but it has its drawbacks. RT-PCR sensitivity can be as low as 60 to 70% and the causes for the false negative results are one defective kits, two insufficient organisms due to inappropriate collection which means the technique for taking that swab has to be correct and thirdly, less patient viral load. So that is why RT-PCR needs to be avoided in the first four days of the illness when the viral load is low. Also RT-PCR takes hours or even days before the results are available and that puts a strain on the holding units. Now what does that mean? It means that patients come to the emergency with common symptoms like dry cough and fever. Now the attending doctor has to wait for hours for the RT-PCR result to come before they can put this patient to the isolation of the COVID ward or to the normal ward and this is where the role of imaging comes in. With imaging results the doctor can now take a quick decision as to whether to send the patient to COVID ward or the normal ward. Now when I say imaging I'm going to talk primarily on the role of CT and not of X-rays that is simply because CT has a sensitivity of 84 to 94% whereas X-ray has a sensitivity of 60 to 67% and not only that most of the literature available is based on CT scan. So CT is not just a diagnostic tool it is also used for prognostication for evaluating disease progression and for monitoring response to therapy. So let's come straight to the CT features of COVID-19 pneumonia. What do we get? The hallmark of course is the ground glass opacities which is usually peripherally distributed like this or they're rounded like this. Now there is a predilection for both lower lobes and usually both the lungs are involved. When these ground glass opacities are interspersed with interlobular septal thickening we get the crazy paving appearance very typical again in COVID-19. Consolidation mixed with ground glass opacities or pure consolidation is also seen. Vessel dilatation now if there is one feature which differentiates COVID from other viral pneumonia it is vessel dilatation and the path of physiology behind it is pulmonary vascular pathy and micro thrombus formation. So you can see the vessels which are dilated over here in comparison to the adjacent normal lung not just dilated they also become more tortuous and they proliferate as the disease progresses. Now there are fancy names that are given to this dilated vessel sign the dandelion sign where the flower represents the ground glass opacities and the stem represents the dilated vessel running through it and also the feather sign where you have the ground glass opacities and at the center of which is the dilated vessel with the dilated side branches. There is also the subplural band which probably represents atelectasis of lung and we get the subplural lines when the disease resolves or in the resolving phase of the disease. We also get some typical features of organizing pneumonia like the reverse halosine where you get central ground glass opacities surrounded by the denser opacities or consolidation or we get a peri lobular pattern of ground glass opacities or consolidation or we get features of architectural distortion. Now the clinician is interested in this phase because this is when they start the patient on steroids. Target sign now this is really a manifestation of the vascular pathy we can see the organizing pneumonia kind of appearance with a central dot over here which represents nothing but the dilated vessel with information around it. Plural effusion is not a common feature but we get plural effusion in the severe stages of the disease. Temporal changes of COVID-19 pneumonia means changes in the CT pattern with time. We have the early stage, the progressive stage, peak stage and the absorption stage. Let's see how the stages look like. Here in the early stage which is 0 to 4 days we can see there's some subtle ground glass opacities and there are less number of lobes involved and there can be some partial gravy paving appearance which is not there in this case. In the progressive stage which is 5 to 8 days you can see that the disease has become much more progressive with the extension of the GGOs and also there is crazy paving pattern. Next comes the peak stage which is at 10 to 13 days where you get consolidation which is usually not pure consolidation like this. It's usually a mixture of consolidation and ground glass opacities. And finally the absorption stage which is more than 14 days where you get gradual resolution and you can see over here the peridobular pattern which means that the pneumonia is organizing. So you can see here the extensive ground glass opacities, the absorption stage with the peridobular pattern and finally complete absorption. Time framed mentioned in literature of the CT changes over time is not always adhered to as you can see in this case where a milder form of disease actually starts organizing as is evident by the architectural distortion which you can see on the sixth day of the disease. Coming to the complications secondary bacterial infection is quite a common complication and also secondary fungal infection is often seen. We have the dreaded complication of acute respiratory distress syndrome when the cytokine storm sets in and it usually is at 8 to 12 days. 20% of all patients are involved and 40% of all hospitalized patients. Now the CT features that we get are not any different from any other cause of ARDS where you have a posterior gradient of the ground glass or air opacities with ground glass opacities anteriorly and the more denser opacities of consolidation posteriorly. White out lung is a term that we often hear with COVID it really means a severe form of ARDS. Here we see a patient with ARDS with pneumomedia stynum obviously because the patient was on ventilator and the positive pressure ventilation has ruptured the already weak alveoli and has caused the air to seep into the media stynum. A rise in D dimer may indicate that there is pulmonary thromboembolism. Remember these patients are already on antithrombotics because thromboembolism is anticipated in this disease and so the thrombus that we get are usually quite small but having said that we can get larger thrombus. So how do we report a COVID CT? Now the Dutch radiological society has come up with the Coread system where we mentioned the level of suspicion of COVID-19 infection. It ranges from Coreads 1 to Coreads 5 where Coreads 1 would mean no suspicion at all and Coreads 5 would mean very high suspicion. Similarly the RSNA expert consensus has also come up with a similar classification where depending on the CT findings they call it typical appearance, indeterminate appearance, atypical appearance or negative funimonia appearance. Let's have a look at some of the examples. So when we get a completely normal CT like this or a CT where there is no evidence of infection, it is a non-infectious disease ILD in this case, we call it Coreads 1 or negative funimonia appearance. When we get centri-lobular nodules or consolidation in a non-peripheral distribution or cavity like this, we know that there is some infection but it is not COVID, we call it Coreads 2 or atypical appearance for COVID. When we get a single focus of ground-glass opacities in the periphery like this or small nodular ground-glass opacity like this, we can call it Coreads 3 or indeterminate appearance or if we get ground-glass opacities or consolidation in one lung or ground-glass opacities in a perihyla distribution or multiple focus of ground-glass opacities but not quite in the peripheral distribution, we'll call it Coreads 3 or indeterminate appearance for COVID. Again, if we get crazy paving appearance like this in a patient who's come with fever and dry cough but it does not fit into the typical features of COVID, we'll call it Coreads 4. And finally, when we get ground-glass opacities in a peripheral distribution or rounded patchy opacities like this or organizing pneumonia kind of appearance, we'll call it typical appearance of COVID or Coreads 5. Once you diagnose the typical appearance of COVID, the clinician now wants to know the CT involvement score. In other words, how much of the lung is involved. Each lobe is given a maximum score of five points, so the five lobes add up to 25 points, so score one would be less than 5% involvement, score two 5 to 25%, score three 26 to 49% involvement, score four is 50 to 75% and score five more than 75% involvement. So in an example like this, I will see the images in the actual coronal and sagittal plane and then I will do an eye estimation and decide how much of the lung is involved. For example, in the right upper lobe, I would say that five to 25% involvement is there, so I'll give it a score of two. Right middle lobe, there is no involvement at all, so I'll give it a score of zero. Right lower lobe seems to have the maximum ground-glass opacities, so I'll give it a score of three because I feel it's 26 to 49% involvement. Similarly, left up a low five to 25% is score of two and left lower lobe, again a score of two. I add up the score and comes to nine out of 25. Now does the scoring have any bearing on the treatment of the patient? Not really, but it does have an implication on prognosticating the patient because it has been found that patients with higher score have higher mortality, morbidity and longer hospital stay and finally can be radiologists actually differentiate COVID from other viral pneumonia. Now a lot of papers have been done on this including this one in RSNA and they have found that the most discriminating features are the ground-glass opacities in peripheral distribution and vascular thickening. Most papers in literature have similar discriminating features. This patient of swine flu, for example, have centrilobular nodules, a lot of pleural effusion which is conspicuous by its absence in COVID-19 and also we find consolidation which is not peripheral and involving one lung and so it is unlikely to be COVID and so with this I come to the end of my talk. Thank you very much, take care, stay safe.