Hi, I'm Judy Yee from Montefiore Medical Center of the Albert Einstein College of Medicine. I'd like to thank Arsenaic for the opportunity to speak with you about CT colonography, interpretation and new techniques. In this talk, I'll review with you the characteristic features of polyps. I'll then focus on sessile serrated lesions, which tend to have flat morphology and are more difficult to identify unless you have positive oral contrast. I'll then provide for you an update on C-Rads and the development of version 2. I'll end off with a discussion about new techniques for CTC, including dual energy CT and artificial intelligence. So polyps are typically sessile in morphology and are rounded or ovoid homogeneous soft tissue lesions. These are the categories that you use for sizing. So diminutive polyps are 5 millimeters or smaller. Remember that you do not need to report these lesions according to the ACR practice parameters. 6 to 9 millimeter polyps are small size category and 10 millimeter and above are the large size polyps. This is the data to support the ACR recommendation not to report the diminutive polyps. So 1 to 5 millimeter polyps, you can see that there is a 0% chance that they are frankly malignant according to this data and a less than 2% chance that they harbor advanced histology. For about small size polyps, 6 to 9 millimeters, well, there's a less than 1% chance that they're frankly malignant and about a 11% chance that they harbor advanced histology. So these do need to be reported. Excellent demonstration of a pedunculated polyp, nicely shown on both 3D and 2D, you can see the stock as well as the large size of the polyp head. Flat lesions are more difficult to identify. And here on the colon windows may be hard to see, but soft tissue windows demonstrates this flat lesion better. And here's a patient on the supine view, you can see that there is this contrast coating on top of this flat lesion. So positive oral contrast can adhere to the surface of the lesion and highlight the lesion for your eye. And here it is on the prone view. Here's another patient, but similarly, you can see that there is a isolated layer of contrast right on top of this flat lesion. Another patient, and you can see again, supine prone and on the NPR, a nice demonstration of this contrast coating. Now, this was a study looking at 160 flat polyps, a mean size was a little bit over nine millimeters. And you can see that 80% showed this thin contrast coat. There were three factors that were associated with the coating. Size larger than 10 millimeters, proximal location, and if there was serrated histology. So the World Health Organization has divided the serrated lesions into these three categories. You have hyperplastic polyps, these are benign, representing 70% of serrated lesions. You have a serrated lesion representing 25% of serrated lesions, and these are potentially malignant. And then you have the least common, traditional serrated adenoma, representing 5% of serrated lesions. And again, these are potentially malignant. The good thing about these two is that they exude a mucin cap, and it's believed that this mucin cap is what the positive oral contrast agent is attracted to and is what causes the contrast coating. Now we do know that serrated neoplasia has a different genetic pathway for the development of cancer. You can see for both traditional serrated adenoma as well as sessile serrated lesion that it starts with a K-RAS or B-RAF mutation. There is then a successive aberrant methylation of tumor suppressor genes that leads to the development of carcinoma. Now this was a study that looked at AI for identifying serrated lesions, and you can see that contrast coating was identified in 91% of lesions. Then an AI algorithm was developed to identify the contrast coating. When this was performed, you can see per lesion sensitivity for both small as well as for the large lesions was really excellent at 96 and 94%. Okay, let's move on to C-RADS. Now C-RADS, as some of you may know, was one of the original RADS to be developed back in 2005, and there's a classification scheme included for both colorectal findings as well as extracolonic findings. Many studies have used C-RADS, and there's been proven utility since its inception. There's continued increase in implementation, not just in the United States, but globally. We are developing and working on a C-RADS version 2, and this is really to help us figure out how to deal with mass-like diverticular strictures as well as to help us to streamline classification of extracolonic findings. So let's briefly review C-RADS. So C0 is inadequate study or awaiting priors. There's no specific linked recommendation. C1 is a completely normal study, or if you have no polyp that's 6 millimeters or above, so you can have diminutive polyps. A benign lesion such as diverticula or lipoma, and then routine screening every 5 to 10 years is recommended. C2 is if you have one or two small, so 6 to 9 millimeter polyps, and then the patient can undergo surveillance or optical colonoscopy. C3 is if you have one or more large, 10 millimeter or above polyps, or three or more small polyps, and then the patient goes on for colonoscopy. And finally, C4 is if you have a suspicious malignant appearing mass, the patient goes on for colonoscopy and a surgical consult. So here's a patient, 56-year-old woman, asymptomatic, who comes in for screening CTC. And what you see is this large lesion on both the 2Ds and the 3Ds. And when you look at the density, though, it's the same density as the periclonic fat. So this turned out to be a lipoma. And so this is a C1 lesion, routine screening every 5 to 10 years. What about this case, a 70-year-old asymptomatic man who comes in for screening CTC? Well, there are three lesions in this patient located in the right colon. Remember that you scored the exam according to the most advanced finding. So here it would be the 19 millimeter sessile polyp. There's also a 12 millimeter sessile polyp. And then this lesion actually turned out to be a lipoma. And so this turned out to be a C3 lesion. ERADS, okay, so E0 is if you have a limited exam or artifacts. E1 is a normal or anatomic variant. E2 is a clinically unimportant finding. And E0 to E2, there's no additional workup that's indicated. E3 and E4 are really the significant categories. E3 is if you have a likely unimportant finding. And then the patient may go on to additional workup depending upon the clinical situation. E4 is if you have a potentially important finding like a solid renal mass, adenopathy, aortic aneurysm, or suspicious lung nodule. And then you communicate the workup to the referring physician according to practice guidelines. So here's a 55-year-old man who's asymptomatic, comes in for a screening CTC, and he has a large right adrenal myelomyeloma. So this is an E2 because it's a clinically unimportant finding, and no additional workup is indicated. Here's a 68-year-old woman with no significant prior medical history. On the non-contrast CTC, you can see that there is a bulge in the left kidney correlated following contrast. You can see clearly there's enhancing renal cell carcinoma with abundant retroperitoneal adenopathy. So clearly this was an E4 lesion. This was a study to help develop benchmark values for the C category of C-REDS. And you see positive cases again are the C2 to C4 categories. And when they looked at the numbers, you could see that the positivity rate in screeners, which is a study only in screeners, is at 14.4%. Again, positive values are for C2 through C4. Of note is that, therefore, 86% of cases are actually negative. The colonoscopy referral rate was much lower, though, at 8.7% because some of the C2 lesions actually decided to have CTC for follow-up rather than optical colonoscopy. Now, also what was found is that the positivity rate for C2 to C4 increased with increasing age. And again, that makes sense because we know that as you get older, you continue to increase in terms of development of polyps. What about E-REDS? So this was a similar study that helped to develop benchmark values for the E score as a part of the C-REDS scheme. And here you can see that the positivity rate for E3 and E4, the ones that require additional follow-up, was at 13.4%. The actual workup rate, though, was at 5% to 6% as demonstrated in the study by Michael Zalas. Now, also what was found was that the positivity rate increased with increasing age. And again, that makes sense because as you get older, there are more abdominal aortic aneurysms, for example. So we know that there's increasing incidence of extracolonic findings as you age. Okay, let's move on to new techniques. And what I have listed here is really research that needs to be performed to help us to continue to increase adoption of CTC. This evaluation in younger patients, we know that the American Cancer Society and the U.S. Preventive Service Task Force lowered the start of screening to age 45 from 50. And so we need to do some studies to evaluate the effectiveness of CTC in younger patients. Decreasing the rigor of the prep as well as decreasing dose, again, these are areas where we need to continue to evaluate to increase adoption of CTC. And then newer technology like dual energy CT and artificial intelligence is underway. So this was a study looking at dual energy CT to decrease dose for CTC. And they evaluated standard dose algorithm as well as a low dose algorithm. And you can see that there was no difference in image quality comparing a dose of three millisieverts, which is the standard dose, to the submillisievert dose, which is considered the low dose. Here's another study looking at dual energy CTC and the use of the iodine map. Now, these were patients who did not receive oral contrast but received intravenous contrast. And here you can see when comparing the conventional CTC images to the CTC with iodine map images, sensitivity was the same. However, specificity was significantly higher when you used the iodine map images. So here's an example of clearly polyps and cancers will enhance high iodine content and nicely differentiated from stool. Here you can see that this is stool because there's absolutely no evidence of iodine in this potential lesion. Now, this is a study that's underway looking at conventional versus dual energy CT electronic cleansing. And in particular, this was looking at the dual layer detector spectral CT scanner. And so there were two experimental cleansing algorithms, transparent and translucent, compared to the conventional cleansing algorithm. What was found was that the spectral transparent and translucent algorithms showed improved scores when looking at the under cleansing artifact. Now, additionally, what was found was that the overall readability was significantly improved in both transparent and translucent algorithms. What about the use of artificial intelligence for CTC? Well, it's being evaluated for lesion detection, in particular for the CESL serrated lesions. For lesion characterization, can we differentiate benign versus premalignant versus malignant? And then for dual energy CT for electronic cleansing. There has been some work looking at AI for extraclonic findings as well. So this was a study looking at machine learning for predicting benign versus premalignant polyps. They used a training set as well as an external validation set. You can see that when they evaluated the external data set that there was excellent area under the curve for both small and for large polyps. So very promising. And this was a study looking at deep learning for electronic cleansing on CTC. And you can see that here's a small polyp on the uncleansed. It's completely submerged so that you can't even identify it. On the conventional electronic cleansing, you can see there's this artifact that obscures the polyp and completely can't see it on the 3D view. Here with the deep learning using dual energy CT for electronic cleansing, you can see that that cleansing artifact is removed and you can identify the polyp. So I wanted to leave you with this resource because it's always up to date and very helpful. It includes pretty much everything that you need to perform CTC. So this is from the American College of Radiology. So my concluding points are that we really recommend the use of oral contrast, which highlights these serrated lesions. C-RADS version 2 is in progress and look for that in a couple of months. There are new techniques that are being evaluated for CTC. This includes dual energy CT and artificial intelligence in particular to help us with improved electronic cleansing. And as well, the good news is that machine learning has already been used successfully to help us to distinguish benign from premalignant polyps. Thanks so much for your attention. Good afternoon. I would like to take this opportunity to thank Dr. Jane Wang and Dr. Judy Yi for giving me this opportunity to present at this year's RSNA. And my apologies for not being there in person. And so the next 15 minutes or so, we are going to be discussing on how MR can be a very useful imaging tool for assessing patients who have enorectal fistulas. So to begin with, we'll be talking about anatomy and technique and how to perform these exams and what is the relevant anatomy. We'll talk about classification and some of the key terminologies that you need to be familiar with when you are describing MR findings in patients with these fistulas. And then lastly, we'll go over the points that need to be incorporated in the structured report that is essential for communicating the key points so that adequate treatment is instituted. So in terms of the anal canal anatomy, if you think about it from an anatomic perspective, what defines the anal canal is the anal canal is the distal most portion of the GI tract. And it extends from the anal verge up to the level of the dentate line, which is the line that defines the junction between the columnar epithelium and the squamous epithelium. The problem with the anatomic definition is that it's very difficult to replicate on MR. And so we try and go with what is the surgical definition of anal canal. And the surgical definition of anal canal is when the surgeon does a digital rectal exam, they feel the top of the puborectalis muscle. And so the puborectalis muscle is easy for us to identify in MR as we'll be seeing in a bit. And so that's the definition of the anal canal that we use. So it essentially is the distance or the distal end of the GI tract extending from the anal verge to the top of the puborectalis muscle or the top of the rectal shelf. So there is a slight discrepancy in terms of anatomic and surgical definition, but the surgical definition is what is implied when one is talking about MR. And in this area of the anal canal, we are talking about two key muscles. We have the internal sphincter and we have the external sphincter. The internal sphincter is in continuation with the circular smooth muscle of the rectum. It is an involuntary muscle and it is contracted during rest and relaxes at the time of defecation. Outside the internal sphincter is the external sphincter, which is a voluntary striated muscle. And it is divided into three distinct fascicles, which function as a single unit. Above the level of the external sphincter is the puborectalis, which is part of the liver-anus muscle. And this is the muscle that defines the extent, the lower margin of which defines the extent of the anal canal. And then extending laterally from the puborectalis is the iliococcigious muscle, which is again part of the liver-anus musculature. So let us see how we translate this into MR. So the coronal plane is the ideal plane for assessing the anatomy of the anal canal. So we have a diagrammatic representation of what the anatomy looks like. We have the coronal T2-weighted sequence and this is a superimposed diagram on the T2-weighted sequence. So you can see outlined in pink is the iliococcigious muscle, which is this fan-shaped muscle on either side. Below that in blue is the puborectalis muscle. And again, the inferior margin of which is where the anal canal begins. And then inferior to the puborectalis is the external anal sphincter, which is outlined in red. The internal sphincter is a direct continuation of the smooth muscle of the rectum. And as you can see here, it extends below to the level of the distal anal canal. Between the external and the internal sphincter is the T2-bright area, which contains SPIAT and that is the intersphinctric space. Now looking at, can you tell the location of the dentate line or can it be inferred on the coronal weighted sequences? And so if you were to take the inferior margin of the puborectalis and join a line connecting the two, that in a sense is the inferred location of the dentate line, which you can correlate. And it is important to know that because most of the fistulas arise in the vicinity of the dentate line. And so knowing this landmark is key for you to identify fistulas. Now one other point in terms of distinguishing internal and external sphincter, the internal sphincter on T2 has a brighter signal than the external sphincter, which is the voluntary muscle. The external sphincter has a similar signal intensity as the obturator internus muscle, whereas the internal sphincter is brighter. Again, on the axis showing the same T2 distinction between the internal and external sphincter. Internal sphincter also enhances earlier compared to the external sphincter. So that is another way of distinguishing the two. One important point about the external sphincter, as I mentioned, there are three distinct fascicles. And so it is important to keep that in mind because that divides the external sphincter into the proximal third, mid third and the lower third. And this becomes key when one is talking about high or low fistulas. So that is an important anatomic aspect that you have to keep in the back of your mind. Now if you were to translate this coronal anatomy to axial, if you take an axial image at the level of the puborectalis muscle, it is this U-shaped muscle that encircles the anorectal junction, which is again depicted in a different patient right here. And it is very easy to identify on MR. Below that is the actual anal canal. And again, you are seeing the internal sphincter, which is brighter compared to the external sphincter. And we have fat in the intersphinctric space. And finally, absolutely at the distal end of the anal canal, right at the level of the anal verge, you only have the external sphincter because the internal sphincter stops a bit short of the most distal aspect of the anal canal. So that is sort of the anatomy of the sphincters now in terms of what are the spaces that are lateral to the sphincter mechanism it is important to keep that in mind and there are two spaces that you have to keep in mind above the level of the puborectalis it's the rectum so the space that surrounds that is referred to as the oscurectal fossa and below the level of the puborectalis you have the anal canal and the space that surrounds it is referred to as the ischioanal fossa so it's important to keep and this distinction in mind because when you have abscesses from fistulas that extend into the relevant spaces you have to be accurate in your terminology in terms of defining whether it's an oscurectal fossa or an ischioanal fossa and then above the level of the levator muscle is the supralevator space so again these are important anatomic distinctions to keep in mind and communicate How do you perform an MR? This is essentially the core protocol that you can utilize to answer all the relevant questions. You start with the triplane localizer then you do three planes of the T2 weighted sequences which are done without fat saturation. These are the key anatomic sequences that lay out the anatomy of the sphincter complex in the anal canal. We have the axial and the coronal STIRS or fat saturated T2 weighted sequences. These are the sequences that delineate the anatomy of the or rather the presence or absence of the fistula and then you correlate it with the anatomy on the non-fat saturated T2 weighted sequence and then you have the fat saturated axial and coronal T1 weighted gradient echo sequences that are done before and after the administration of gadolinium that are useful complements to the STIRS sequences for identifying presence or absence of fistulas. So that is in a nutshell the anatomy and the technique. Now let us talk about classification. So there are various ways that you can classify fistulas. The most commonly used is the Park's classification because it is a very simplistic delineation of what the anatomy or what the anatomy of the fistula as it translates into the various types of fistulas. The St. James classification is a slight modification of the Park's and then we have the American Gastrointestinal Association classification that divides the fistula into two broad categories. So let us start with the Park's classification which most of us use in terms of delineating or identifying the fistulas. And so if you look at the diagrammatic representation and the key categories, the four common categories are the interspentric, the transcentric, supra and the extraspentric. But there is a type of fistula which is referred to as a superficial fistula which is outlined in green here and this is the fistula that does not transgress any of the sphincter mechanism. It basically is located very low in the anal canal and starts in the lumen and extends the skin and barely extends beyond the wall of the anal canal. You can get this type of fistula especially in those patients who do not have Crohn's. The vast majority of the patients that we see are patients with Crohn's disease and it is usually one of these four types where the inter and the transcentric are the most common types of fistula. So let us look at what constitutes the anatomy of this individual four subtypes. So interspentric as the name implies is when the fistula begins in the lumen of the anal canal, goes through the internal sphincter and extends down to the skin between the internal and the external sphincter. Because it extends between the internal and external sphincter, it is referred to as an interspentric fistula. So here is an example of an interspentric fistula. You are looking at the T2 non-FATSAT. This is the T2 with STIR and this is the axial gadolinium enhanced FAT-saturated T1 weighted sequence. So as we move down, you will see that here is the fistula which is present at 6 o'clock in position identified on the STIR as well as on the anatomic sequence as well as on the gadolinium enhanced series and you can see that it extends. That is the beginning in the lumen and it is going in between those two sphincter complexes and extending down to the level of the skin. It does not transgress the external sphincter. Here is another example where you can see on this T1 weighted gadolinium sequence, the fistula begins at 6 o'clock. There is a slight track between the two sphincters and so it is referred to as an interspentric track and on the coronal, you can see it is making its way down to the skin between the internal and external sphincter. So that is what interspentric fistula looks like. Transphentric fistula begins in the anal canal, goes through the internal sphincter, goes through the interspentric space and then extends through the external sphincter before it makes its way down to the skin. So as the name implies, transphentric, it means it goes through both the internal and the external sphincter compared to the interspentric which only goes through the internal sphincter. So let us look at what this looks like on MR. So here is an example where you are looking at the axial stir and as we march away, you can see that the fistula is originating at 6 o'clock in position. It is transgressing the internal sphincter right here and again goes through the external sphincter and then makes its way down to the skin. So this is an example of a transphentric on axial image. And here is another example. On stir, you can see the fistula starting posteriorly going through the two sphincter muscles, going into the ischial space as it makes its way down to the skin. And here is another example on the right side where you can see that there is a seton or a string that outlines the fistula's track. It is beginning in the lumen going through the two sphincter muscles and extending down to the skin in the ischial space. The supra and the extrasphinctric fistulas are not as common. They are, albeit can be seen in patients with inflammatory bowel disease. So the suprasphinctric fistula is where the fistula begins in the lumen of the anal canal. Instead of extending down, it goes through the internal sphincter and then extends superiorly in the intersphinctric space and then extends down as it pierces the levator ani muscle lateral to the sphincter mechanism. So supra meaning it goes superior instead of extending down. So let us look at an example. So here is a coronal nonfat sac and this is a stir sequence. You can see the fistula is beginning here in the lumen and it goes above. And as you can see on the anatomic pain, it goes above the levator and then pierces the levator and extending down lateral to the sphincter mechanism. Here is another example. So as I scroll through the images, you will see that there is a track on either side and that fistula is originating right here and extending above the levator and then extending down. There is one track that comes down on the right, the other track goes down on the left. But the origin is within the lumen of the anal canal extending superiorly piercing the levator muscle and then extending lateral to the sphincter complex. And then the last is extrasphinctric which the name implies it actually begins in the rectum not in the anal canal and pierces through the wall and extends through the levator muscle sparing the anal sphincter complex. That is why it is called extrasphinctric which means outside the sphincter complex. And this is what it looks like. You can see this is a fistula that is beginning in the rectum and then extending down on either side as you can see on the axial images of the sphincter muscle. And here is another example where you can see the fistula is originating high up in the rectum and extends its way down to the skin. So that is sort of in a nutshell the classification of the commonly used classification of the fistula. This is what we typically use. Now in terms of the AGE, the American Gastroenterology Association simple versus complex fistulas, it is important to understand two key terms. One is what constitutes an abscess and what constitutes high versus a low fistula. And so if you look at these three images with the non-FATSAT T2, the STIR and the gadolinum enhanced image, what you see here is a fistula's track and it is bright on T2. The question is when you look at the T2 images, is it an abscess or not? You have to look at the gadolinum enhanced image and you can see that there is no part of the fistula that shows lack of enhancement. The entire tract is enhancing. So this is inflammatory tissue and it is not an abscess. In contradiction, look at this example where you can see a large posterior T2 bright area which again shows peripheral enhancement and the central part is not enhancing and that is an abscess cavity. And you know there are various size criterion. We use a threshold of 3 millimeter to define a cavity. So what constitutes an abscess in terms of definition? It is an area that shows rim enhancement on the T1-weighted post-gadolinum enhanced images. It is greater than 3 millimeters in diameter in at least two dimensions which does not include the tract that leads up to the abscess. And ideally when you have an abscess, you measure in all three planes. So you measure the AP dimension, the transverse dimension and cranial caudal dimension and put that in your report. And it is done on the T1-weighted post-gadolinum. That is a very key sequence to establish the definition of an abscess. The high versus low, again as I mentioned earlier, you have the external sphincter that is divided into thirds. So if you have a fistula that transgresses the proximal or the upper two-third, whether it is trans or intrasphinctric, that is referred to as a high fistula. Whereas if the fistula is at the level of the lower one-third of the external sphincter, then that is referred to as a low fistula. So in terms of looking at, here is an example where as I scroll through, you can see that this is a transphinctric fistula that is traversing the upper or the proximal two-thirds of the external sphincter making this a high fistula. And you would put that in your report in addition to the descriptor. So this would be a transphinctric and is a high fistula with lack of an abscess cavity as we see in this case. This is a high fistula. And here is an example of another intrasphinctric where it clearly is at the level of the lower one-third of the external sphincter. So this would be classified as a low intrasphinctric fistula. And so that is sort of in a nutshell looking at high versus low. Now lastly, just in terms of what do you include in the report, these are the key attributes that you need to put in your report. Is there a presence or an absence of fistula? How many fistulas are there? Now this is contingent on the number of internal openings that you see in the anal canal. Each fistula needs to have one internal opening. If you have more than one internal opening, then you have more than one fistula that is present. You classify it using the parts classification. You talk about the location of the internal and external opening based on the clock face. So if you were to take an anal canal and there is a fistula that is arising posteriorly, so you would say that's at six o'clock. Or if it's arising anteriorly, that would be at 12 o'clock. So that's how you establish the clock face in terms of where the internal opening is. You talk about the internal opening in relationship to structures, internal structures like the puborectalis, anal vertebrae. You communicate whether it's a high or low based on what's the level of the external sphincter that is involved. In terms of anatomic extension, you talk about whether it's extending in the intersphinctric space or whether it's going above the labial muscle. If you have an abscess, then you have to tell or communicate to the surgeon whether the abscess is in the osteorectal fossa or is in the osteoanal fossa. Is there a seton, which is a string that is used to either heal the tract or drain the abscess cavity, whether that's present or not. And then finally, in inflammatory bowel disease, you talk about whether there is rectal thickening present or not. In this instance, you are seeing marked thickening of the rectum with enhancing nodes because again, that plays a key role in terms of adequate treatment of these fistulas. So in conclusion, I think we have gone over some of the key points that are required in MR interpretation of anorectal fistula. I would like to point to this article that came out in European Radiology, which is a consensus document released in 2020, which goes through some of the key aspects of definitions that you need to know as well as talks about some of the key things that you need to make sure you include in your report. So with that, I'll stop and thank you very much. My name is David Kim. I'm from the University of Wisconsin, and I will be talking to you on practical tips to optimize CT colonography. So in the short 15-minute lecture, we're going to talk about the technical components of CT colonography, that of bowel preparation and colonic distension. We'll see how we can best optimize these portions of the exam, as well as troubleshoot when things go wrong, then finish up with some summary comments. So CT colonography is certainly a complex exam, you know. It's scanning. We scan the person on their back, again on their stomach. We do it in end expiration so the lungs don't push on the transverse colon. We actively QA. We do additional modifications, additional series, in order to make sure we have really optimized images for interpretation. But besides scanning, there are a lot of parts of the exam that we have to do, and we have to do well, including the bowel preparation and colonic distension. And we know if we have better bowel prep, better distension, the interpretation is easier and more accurate. So let's focus in on bowel preparation. So CT colonography has been around clinically 15-plus years, and it's become evident the optimal regimen is one that combines cathartic agents and tagging agents. And so the paradigm is you purge the colon. All the internal contents go. Anything left behind is tagged. And the trial data supports that approach. National CT colonography trial, published in the New England Journal in 2008, you can see that the sensitivities are 90 percent at the 10-millimeter threshold, and then it drops down to an acceptable close to 80 percent at the 6-millimeter threshold. And if we deviate from this paradigm, then we pay a price. You know, there's an active investigation to get rid of the cathartic portion, right? We just tag it. We leave all the bulk stool in and tag the images. And when you look at the data, performance falls off. So sensitivity is still great at 91 percent at the 10-millimeter threshold, but it drops down substantially, close to 60 percent at the 6-millimeter threshold. So when you tag things, and also what these numbers sort of understate is the fact that it is a really difficult exam to interpret. When you look at tagged stool, sometimes you say, okay, there's possibly a polyp here, and then you're wondering, is this just untagged stool, or is this truly a polyp? So hopefully it's obvious that cathartic regimen, or cathartic part of the preparation is a cornerstone. And so you want to do everything you can do to cleanse the colon. So when you have a well-cleansed colon, you can see how easy it is to evaluate the colon for soft tissue polyps, as opposed to the situation where you have a poorly cleansed colon with a lot of residual stool that you need to interpret. They're going to all look like polyps, and then ultimately dismiss the pseudopolyps related to stool. So here on this left, there's this polyp candidate that turned out to be a true soft tissue polyp. If this was here in this poorly cleansed colon, there's a good chance it would be lost in a sea of pseudopolyps. Besides cathartic agents, you have to tag well. When you have a polyp candidate and you have tagging on board, it's really easy, right? The tag, the stool incorporates the tag, raises its attenuation number, becomes white in appearance. So it does not look like a gray soft tissue polyp. If you don't have tagging or you have poor tagging on board, then what happens is that piece of stool, as we see here posteriorly in the transverse colon, looks like a soft tissue polyp. So what you need to do now is find it on the other view. You can see here's the prone series, and you can see that there is movement to the anterior wall falling to a dependent location. So several more steps in order to confirm that this is a pseudopolyp related to stool. This becomes even harder when the underlying colon shifts between supine and prone positioning. So again, if you have tagging on board, it's a very, very easy sort of distinction and quick. If you don't, then it becomes a lot more involved and a lot more intensive. So hopefully it's obvious to you that you want to use both catharsis and tagging. But even if you use that approach, there are numerous specific regimens that you can use. And I think that's unfortunate, because although all of these regimens cleanse and tag well, their sort of impact on polyp coding is largely unknown. And what we've come to realize over the past couple of years is that polyp coding is the way we find flat sessile serrated lesions. I'm going to talk more about this as a really important sort of concept. So I wanted to highlight one specific prep where we know how it interacts with polyp coding. And that's the prep we use at Wisconsin. It's a dry cathartic dual tagging prep. And I'll put this up at the end, the specifics of the protocol, on the last slide. So it's a dry cathartic prep. And what that means is it generates minimal amounts of colonic fluid. It's two bottle. It's a maxitri. And then it's dual tagging, both barium. We use dilute 2% barium. It's CT barium. That is done to tag predominantly stool. And then iohexol, which is iodine-based, to tag fluid. And we know that this regimen of a dry cathartic dual barium iodine tag leads to polyp coding, which then we can find sessile serrated lesions. And we've published our experience with sessile serrated lesions. Our prevalence is 3.1% for non-diminutive lesions. These are typically large lesions in the right colon. But they are subtle because they are flat. And the way we find these lesions is through polyp coding. When it's present, it increases the odds ratio of detection by 40. All right. So let's look at these really important lesions. Hopefully, you're aware of this precursor polyp. This was just recently described in the last decade or so. And it previously was misrecognized as a benign hyperplastic polyp. This is similar to a hyperplastic polyp, but holds malignant potential. It's a different pathway from adenomas. So if you look at this lesion, notice it's a really flat lesion. It's pretty subtle. You can see between these two house straw folds. If we had to rely on morphology, sort of the height above the mucosa, we would be missing these lesions. It would be very difficult for us to detect it at CT colonography. In addition, it would be so labor intensive, you probably wouldn't want to do CT colonography. But we can see these lesions, and the detection method is super easy. And the reason why is these lesions elaborate a mucin coat that you see here. If you were to wipe this away, you would see a flat polyp underneath it. That mucin coat adheres to the surface of the flat polyp. Our tagging agents mix with it and creates a polyp coat. Again, dry cathartic dual tagging prep, we know this occurs. If you were to substitute polyethylene glycol, a wet cathartic, or just do a single iodine tag only, whether or not polyp coating truly occurs is unknown. So what does this look like at CT? You know, so all we have to do is look for plaques of contrast. So you can see in the cecum right here, we have this bright plaque of contrast that draws our attention to this area. We're not looking super hard for this mild undulation of the mucosal contour. We just look for these plaques of contrast, super easy sort of detection pattern. Once we find it, we put on our list to go ahead and confirm at some point. On 3D, because of the polyp coat, you can see that these lesions are not flat. They look sessile in nature, because of all the tagging agent that's heaped up on that flat polyp. Now once you detect it on both views, you go ahead and characterize it. And you're trying to separate out, is it a coated flat polyp or is it tag stool? And I'm not going to get into all the specifics of doing it. We do have a paper in radiographics on how to interpret these that I would refer you to. It was published in 2017. But I can tell you, our fellows, once they go through a handful of these, 10 or 15 of them, they feel very confident in detecting and then characterizing flat polyps and separating out from an adherence stool. So you can see this flat polyp here detected at CTC screening. This is what it looked like at endoscopy. And that turned out to be a sessile serrated lesion. So in order to optimize the bowel prep, what do we have to do? One, pick the appropriate regimen. And the regimen should have both cathartic and tagging agents on board. It should be something easy for the patient to do. The one we use at Wisconsin, it's a one-day prep, it's three administrations separated by three hours. And then finally, know how it interacts with polyp coating, because if polyp coating is not occurring, you are missing flat cecl serrated lesions. The other really important thing with the bowel preparation is you have to create a process to answer questions. Patients are gonna have a ton of questions when they do the prep. Here's a listing of some of the questions that we get. And so we have a number, they can call our nurse program coordinator, she works them through the prep, answers any questions. If the questions happen in the night, we have a script for our residents to read from to answer the questions. If you don't do this, what happens is they show up at CTC, and I can guarantee you it will be a suboptimal prep and it will impact your interpretation. One of the questions that we always get is, I'm taking the Maxitrate, but it's not really working. And for Maxitrate, because it's a dry osmotic cathartic, you really have to be well hydrated. And these people are relatively dehydrated. So we tell them, drink plenty of fluids. If they don't, this is what happens. You get this kind of sticky tag stool in the right colon. And you can imagine how our sensitivity for detecting flat cecl serrated lesions really decreases when we have a poor prep and it looks like this. Okay, let's move over to colonic distension. In contrast to bowel preparation where there are numerous regimens, there's general consensus on how best to do it. And that is to use automated CO2 insufflation. In the US, we don't use any spasmolytics. And we like it because the distension is much more consistent, and it's easier to determine the endpoints when we should start scanning. We look at volume measurements and pressure measurements. When they get into a certain range, we're good to go. As opposed to room air bulb insufflation, it's done blindly at CT. It's not like at barium enema where you're looking under the fluoroscope to see colonic distension. At CTC, it's a blind sort of set number of puffs and you're titrating to patient discomfort. The other point is that we like it because of the low pressure delivery of carbon dioxide. So there really is no risk for perforation with manual room air insufflation. You can generate some pretty high wall pressures. The key to distension is that the CO2 should be continuously infusing while you scan. What happens is carbon dioxide, unlike nitrogen and room air, which is not reabsorbed, is actively reabsorbed across the colon and mucosa. So even if the person's not refluxing across an incompetent ileocecal valve or letting it out around the catheter, the colon is gonna decompress because it's actively reabsorbed the CO2. So you have to keep the CO2 going in. Once you turn it off, the colon kind of starts to deflate, kind of like a bouncy castle that doesn't have a fan on. So what we do is we start the person in left lateral decube and fill the colon. And what you'll see is the filling pressures will be in the teens when the colon's filling. At two liters, we turn them to right lateral decube. And then when it gets to about four liters, we put them supine. At that point, the pressures will kind of equal out in the mid-20s, and that's sort of the pressures when they're at equilibrium, that is CO2 in equals out. And so they're gonna be optimally distended at this point. So we scout, looks good, we go ahead and scan. Then we flip the person prone and let the pressures kind of settle out, during which time we QA when the pressures go back to kind of the mid-20s. And usually there's another liter or two into the person. We go ahead and scout and scan the prone, ultimately QA the prone. And then depending on what we see, we decide whether or not we need a third series, just default to a right lateral decube. You don't have to worry about it. That will answer any areas that are not completely distended. By the time of the colonic distension, you're gonna have volume somewhere in the range of six to eight liters. Realize this is not how much is in the colon. This is what's gone through the machine. There's always things being reabsorbed. So this is not like if the person has seven liters in their colon. Now, quick point about that volume measurement. You really have to wait to four liters. This is a person that was in CTC screening 2006, 2011. Notice how good the distension is in 2006. It's okay in 2011, but not as good. And so what our techs were doing in order to increase throughput, they said, oh, we hit the equilibrium pressure, it's 25. And it was only about at two liters or so. You really have to wait to four liters. I think colon kind of relaxes over time, and you just get better distension. So certainly at 2011, this is diagnostic. You can make a good evaluation of the colon, but I would argue that when things are distended better, it flattens out the colonic ulcer. It is so much easier to look at this colon and look for significant soft tissue polyps. So practical tips for distension, wait till the four liter mark. The pressures are gonna be in the mid 20s. You have to make sure that the CO2 is going in while you scan. And then if you need a third series, just do a right lateral decube. You don't have to think between right or left, just do a right lateral decube, right side down. All right, so just some quick sort of problem scenarios. One thing you may encounter is frozen volume pressure measurements. And that is the volume numbers don't change at all. This should slowly increase over the course of the exam. There's no variation of the pressure measurements. So these numbers are just fixed and frozen. What's happening is you have a block in the tubing and you'll see that the colon isn't distended. And the block in the tubing is often due to fluid. And so this is the end that goes in the patient. This hooks to the insufflator. You'll see fluid in this tubing. You need to kind of milk it back into this collection bag. So the patient will report starting the prep late and they're still having liquid bowel movements. They're still doing the prep essentially. You wanna drain the fluid back to the collection bag. You can consider getting the patient up so they can use the bathroom or even delay the scan an hour or two. The other sort of, and you have to problem solve with this, right? So in this person, we're in the right lateral decube. The first two ones weren't really well distended. And so we did the stirred view and noticed that it really is not distended well. And we're like, huh, there's no fluid in the tubing. What's happening? So you just trace the tubing and we just happened to position him so he was lying on the tubing crimping it and that's why it wasn't distending. So we repositioned and got better distension. Sort of the final sort of kind of scenario I wanna talk about is where you have poor distension but those numbers aren't frozen. The volume is going up slowly. There is some variation in the pressure measurements but when you scan them, it really is not well distended. And what could be going on, which may not be obvious, is that the person has low CO2 tanks. So this right here tells you how full the tank is. And if it is here in the red, they're nearly empty, then it doesn't generate the pressure it should. So I usually just switch out to new tanks and you'll get better distension. So in summary, you wanna optimize bowel preparation and colonic distension, the technical components, the CTC, will make your interpretation so much easier. For bowel prep, you wanna do an osmotic, dry cathartic, dual tagging, barium iodine. Consider using the UW protocol. We know how it works in terms of polyp coding and cecl serrated lesion detection. For CO2 insufflation, it has to be infusing the entire time that you scan. Thank you very much. Hello, everyone. My name is Zahra Kassam from Western University in London, Ontario, Canada, and I'll be talking to you about some pearls and pitfalls in rectal MRI. So these are our objectives today. We'll talk about some technical pearls. We'll go over some tips, tricks, and myths with regards to T staging, N staging, and prognostic factors and I'll briefly review some restaging pearls and pitfalls. So let's dive into technique. So rectal cancer imaging requires three plane series with T2-weighted images and slice thickness should be quite thin at three millimeters. We should image five centimeters above the edge of the tumor to include the lymphatic drainage. For low rectal cancer, we want to get the coronal plane to assess the sphincter complex. We don't need a bowel prep. Some centers do use it, but it's not required. Rectal and IV contrast are optional. We don't need an endoreptile coil and 1.5 and 3T are both acceptable. So in terms of sequence planning, we want to get the sagittal T2-weighted image first, find the tumor, which is here, and then obtain an axial oblique plane, which is perpendicular to it, resulting in this image here. Sometimes when we're doing our angulation, we can have some pitfalls. So this is an anterior ulcerated tumor. The first angle that was obtained was not perpendicular to the tumor and it looked like there was maybe some T3 disease. When we reevaluated, we went perpendicular and we can see the muscularis is intact. So that's a T2 lesion. Spasmolytics are useful, I think, in rectal cancer imaging. On the left, we have an image that was obtained without buscopan, showing a lot of blurring. On the right, we can clearly see the tumor after buscopan has been given. So I would strongly recommend you use spasmolytics if available at your institution. Diffusion-weighted imaging can actually be quite helpful for detection. So this is a patient where it was very difficult to identify the tumor because of lots of fecal matter in the colon. So we routinely obtain DWI images after the sagittal. And in this case, we were able to identify diffusion restriction corresponding to the tumor. So we triangulated back to the sagittal images and found something here, which we localized for axial oblique. And we ended up actually identifying the tumor here, which was semi-circumferential. And we were able to do our T staging that way. So that's a little trick you can use if you don't see the tumor. So let's move on to interpretation with T staging and CRM. So firstly, what clinical information is needed? Well, we need to know where the tumor is and what the endoscopy report showed. That's very important for planning of the study. We need to know if this is biopsy proven rectal cancer versus secondary involvement by tumor or an inflammatory process. So this is a patient with ulcerative colitis showing lots of edema and inflammation in the rectum. And this can sometimes obscure our interpretation. And it is helpful to know whether the tumor is mucous or non-mucinous. It might change your search pattern and your MR protocol. This is a form we developed at our institution that we ask all of our referring physicians to fill out. Lots of clinical information is required, which is very helpful for the technologists and the radiologists in planning the case. The normal rectal wall is important to be aware of the various layers. So here we have the inner layer, which is low T2 signal and corresponds to the mucosa. The outer layer is also low T2 signal. That represents the muscular is propria and sandwiched in between is the high T2 signal submucosa. T2 versus T3 disease can be quite challenging. If you only use speculation in the fat, the positive predictive value is only 51%. So we need to use something with higher positive predictive value. So tumor bulge and nodular growth in the perirectal fat are much more reliable. And here's an example of a case where there were spicules in the fat, but this turned out to be a T2 lesion. Here we have some nodular growth and intermediate signal thickening, clearly a T3 lesion. Unfortunately, not all cases are that clear cut. Here's a case of a patient who had a tumor that looks like it was confined to the rectal wall, maybe a few linear spicules, but this was staged as T2 pathology. Unfortunately, we did see some cells sneaking into the adjacent fibrous tissue and the adjacent fat. So this was a T3A lesion, but the management did not change in this case. So when deciding between T2 and T3 disease and you have an ulcerated mass, remember that the invasion should occur at the thinnest portion of the ulcer wall. If you have clean fat deep to that ulcer, there's a good chance that you have a T2 lesion. When sequence planning, set up your axial oblique T2 through the deepest portion of the ulcer crater. So here we've got an ulcerated posterior rectal mass. We found the ulcer. We're gonna angle right through the base of that ulcer. And then we get this image here that shows some tumor extension, nodular thickening deep to the fat. If you're still unsure, you can use advanced T2 versus early T3 and the management may not change. Another diagnostic challenge is the anterior peritoneal deflection, which is depicted here. Here's an example of T4A disease in three different patients. So here we have lateral T4A disease. Remember that this is a three-dimensional structure. So you can't have anterior involvement or lateral involvement. And here's another example of the peritoneal deflection being involved. In contrast to this case, this is a patient with a tumor that abuts the anterior peritoneal deflection. So you can see there's no fat and there's clear contact, but the reflection itself is not thickened, not nodular. So not considered T4A disease. Here's an example of a patient who has T4B disease. There's an anterior tumor that involves the seminal vesicles and the base of the prostate, but it's a really beautiful example of a very abnormal anterior peritoneal deflection. It's low T2 signal and nodular and thickened. And you can see the corresponding tumor on the endoscopy. The circumferential resection margin is very important because a negative CRM has an independent or is an independent prognostic factor for high disease-free survival. So our job as radiologists is to determine whether the CRM is threatened. And you'll see I have an asterisk there because really what we're looking at on MRI is the mesorectal fascia. We don't really know what the CRM is gonna be until the specimen comes out. And it's a surgeon's job to achieve an R0 resection with an intact TME specimen. So this is what an intact specimen looks like. Here we're getting variable degrees of defects, coning and irregular excision margins, all of which increase the risk of local regional recurrence and reduce the disease-free survival. Now some myths and must-know facts about the CRM. The status of the CRM depends only on the primary tumor, not the lymph nodes or deposits that are close to it. And when we're measuring, we need to measure the shortest distance at the tumor fat interface. So do not include the uninvolved rectal wall in your measurement. You always measure from the point of rectal wall breach. So here we've got a nodular-looking tumor. It looks like the muscularis is disrupted here. So we're gonna measure from this point of disruption to the MRF. Even though this wall is closer to the MRF, there is no tumor involvement there. So we do not wanna measure at that point. So CRM status can be positive, threatened, or negative, depending on the distance between the breached wall and the MRF. Here's another example of a negative CRM. So here we've got a circumferential tumor. This is where the wall is breached. There's still muscularis here, so we're not gonna measure there. We're gonna make this measurement our reported distance. And even though there's an abnormal node here, the nodes and tumor deposits do not affect CRM status. So now we'll move along to end staging. So as you know, in rectal cancer, we can sometimes see very small lymph nodes, and many of those are benign, but some of them can also be malignant. So keep in mind that positive nodes are often located at or superior to the margin of the tumor because of the direction of lymphatic drainage. We can use DWI for detection, but not characterization in primary staging. In terms of criteria, the smaller the node, the more abnormal morphologic features you need, which include round shape, irregular border, and heterogeneous signal to call a lymph node negative. With restaging, if the node becomes smaller, we can say that it has responded. And if the node is five millimeters or more, we don't have great guidelines, so we say that those are malignant. Mucinous tumors and nodes can have a poor prognosis and are less responsive to chemoradiation, and they can be difficult to stage. They look bright on T2 because of the water content. So inversion recovery or fat-saturated T2 can be helpful for detection. Be aware of a pseudocapsule, which can mimic the muscular aspropria. I'll talk about that in just a moment. And here is an abnormal node, which blends into the fats. We do have to be aware of that when looking at our search. So DWI can also be a pearl for mucinous node detection. Here we have non-fat-saturated images, and there are several nodes that have central high T2 signal. But when you look at the DWI and the ADC, there's through transmission. These should be fat-saturated. So clearly this is a mucinous lymph node. So more mucinous tumors in additional patients and nodes. So keep in mind that sometimes mucinous tumors have a low T2 signal rim around them, which is really a pseudocapsule. It's not the intact muscularis. So what you're looking for is an outpouching. If there is low T2 signal behind that outpouching, that's probably a pseudocapsule. And this patient also had mucinous nodes and a lot of fat-saturated T2. And enlarged non-mucinous nodes, which were suspicious. Also be aware of the low T2 signal node. So this is a patient that had a low T2 signal oval area that was initially called a node. But when we went back to the CT, that was just a flibolus. Some of the prognostic factors to be aware of are extramural vascular invasion, where tumor cells extend into adjacent vessels. We're looking for an enlarged tubular structure with intermediate T2 signal. And that is a biomarker of poor prognosis. The significance of EMVI positivity include poor overall disease, free survival and recurrence-free survival, and is often associated with distant metastasis. So you can see here without EMVI and with EMVI, five-year survival rate is quite different. Another patient with EMVI and a liver metastasis. Tumor deposits are called N1C disease. They do not contain lymphoid tissue, but they're still called N1C, which is kind of confusing. But independently, they do confer a poor prognosis and they have low T2 signal and a shaggy irregular margin. Lymph nodes usually have a more clear-cut circumscribed margin. Okay, so we'll spend a little bit of time on restaging. So just keep in mind that non-operative margin, sorry, non-operative management is being used for several patients now. And a third of patients treated with CRT alone may have no residual tumor after therapy, and that's considered a pathologic complete response. We can't use MRI alone. We need DRV and endoscopy along with MRI, which assesses the superficial and deep layers. So here's an example of endoscopic response assessment. So signs of a complete response include whitening of the mucosa with telangiectasia and normalization of the tumor bed. In this case, we've got a small ulcer and then on the right, we have a larger ulcer. Some of the interpretive challenges when you have a primary tumor and involved nodes are superficial residual tumor within a fibrotic area, viable tumor with scarring, viable tumor that mimics desmoplastic reaction, and superimposed mucin pools that can mask residual tumor. So how do we know there's been a response? Well, if you see restoration of two normal wall layers on T2, that is a very accurate sign of a complete response. Restoration of the fat pad between the tumor and the MRF, we can also assume that the MRF is uninvolved. So here's an example of a patient who had a posterior semicircumferential tumor, and we see some scarring. And this patient had a complete response endoscopically. Here's an example of a patient with a partial response. So here we have a semicircumferential tumor and then some scarring, and we do not see discrete bowel wall layers here. So we know this is probably not a complete response. And here's an example of a patient who developed acellular mucin pools after therapy, which you can sometimes see. So evaluation of lymph nodes, nodal restaging after chemoradiation is actually more accurate than primary staging. And in restaging, DWI can be used to assess lymph node response. So in summary, hopefully you learned some technical tips. Use spasmolytic agents. DWI can be used for detection, but not characterization in primary staging. Angle through the ulcer. T staging and CRM, remember nodular contour and signal intensity. The CRM positivity is only based on the tumor itself, not nodes and tumor deposits. Beware of prognostic factors, including EMBI and tumor deposits. And for restaging, you can use DWI for lymph nodes. Look for fibrotic scars, edema, and mucin pools, and always remember endoscopic correlation. Thank you very much.

medical imaging

CT colonography

MRI

colorectal cancer

anorectal fistulas

sessile serrated lesions

artificial intelligence

bowel preparation

T2 staging

diagnostic proficiency