Dr. Scott Stacy provides a brief history of medical imaging and details the modern day options for imaging.
[MUSIC PLAYING] G. SCOTT STACY: This is going to be a very whirlwind tour of orthopedic radiology in the next 30 minutes. I do have a couple very brief disclosures. I work with Biomet studying sternal fixation that really has nothing to do with this talk. And I will be talking about the intra-articular use of gadolinium, which is an off-label use of the drug. I always like to start this off with a brief history of medical imaging. So if you were standing in front of this building a little over 100 years ago-- you would be in Germany, at the University of Wurzberg-- and if you were to look into this window here you might see this gentleman. That is Wilhelm Conrad Rontgen, who is the father of radiology as we know it. And what he did in his spare time in his lab was to investigate cathode ray fluorescence by passing electricity through gas-filled tubes, kind of like today's fluorescent light bulbs. And then on one fateful day, on November 8, 1895, while conducting these experiments he noticed that some paper that was coated with a substance called barium platinocyanide started to glow. But this was strange because the tubes that he was investigating were actually covered by a cardboard box at the time. So somehow the energy had to get from the tubes to activate the paper, which means it had to go through the cardboard. So Rontgen was understandably very perplexed by this, and he would perform some additional experiments, and in doing so he noticed on this paper that he saw the bones of his hand. The medical world, of course, immediately recognized the importance of this discovery, and soon the literature was filled with medical radiography, such as this picture here, the first American medical x-ray. The first radiologist probably looked at this and said, well, it's either a fracture of the ankle or a fracture of the wrist. Please correlate clinically. And the rest is history, so to speak. So what we're going to talk about today is a fair amount on conventional radiography, some on CT, quite a bit on MRI, and a little bit about nuclear medicine and ultrasound, too. And this is going to be a fast talk, and I apologize for that. But we do have a lot to get through. Some of this has already been talked about before, but I just want to go back to a very basic level here. Radiographs use x-rays, right? And they provide good evaluation of bones, but relatively limited evaluation of soft tissue structures. What we look at for on radiographs are the different densities of various structures. High-density structures, which tend to be white, include bone calcification and metal. Intermediate density structures tend to be gray, such as soft tissues like the Achilles tendon that you see is outlined by the green arrows and a little joint effusion outlined by the red arrows, whereas low-density tissues tend to be dark, such as fat and air. So I have three general suggestions with regards to ordering radiographs. Number one, they should be ordered in general before other, more expensive tests, with a few exceptions, which we'll talk about later. Radiographs may be sufficient for demonstrating pathology, and actually may show a pathology better than other imaging modalities. If additional imaging is needed, please consult with your radiologist-- your friendly radiologist-- and he or she can certainly help you choose the right study. And please supply your friendly radiologist with a differential diagnosis or pertinent clinical history. It really does help in the care of the patient. So a few other suggestions. In the trauma setting, and I know we've been talking a lot about trauma today so I'm just going to reiterate a couple of points. You always want to order at least 2 views of a bone. Generally orthogonal views, although not always truly orthogonal, but a frontal and a lateral view, for example. However, keep in mind that a proper evaluation of some bones and some joints actually requires more than two views, but if you only order two views that's all you're going to get. So we'll talk a little bit about these various important point in these various bones. So here's just a kind of standard example, lateral femur radiograph. It's in a child. We don't see any fracture here, it looks normal on this lateral view. But when you look on the AP view, you can clearly see an oblique fracture, denoted by the red arrows here. So it just goes to show you, the two views at minimum is important. So when are two views appropriate? Well they're appropriate for the long bones, the forearm, meaning the radius and ulna, the humerus, the tib fib, and also the thigh or the femur. So here we see an example of two views of the tibia and fibula. On this one view, the lateral view, if you look very carefully there you can see in fact there's a so-called dreaded black line. This is a stress fracture along the tensile or anterior surface of the tibia. Two views are also appropriate for the proximal joints, and by the proximal joints I mean the hip and the shoulder. So in the hip, you can either get an AP view of the hip like we have here or you get an AP view of the entire pelvis, which has the dual advantages of being able to compare side to side both hips, and also a lot of the measurements we make for hip, for femoral acetabular impingement, for example, are really based on the pelvis radiographs. And you also want to get a lateral view of the symptomatic hip. And there are various different types of lateral views. The most common that we get is a frog-leg view, but there's a Dunn view or modified Dunn view that can be used in case of the femoral acetabular impingement. Again for measurement purposes in the trauma setting, we generally don't want to move the patient's hip, so we get a cross-table lateral view instead to show fractures of the femoral neck. For the shoulder, we get a couple different types of AP views. We get what we call a neutral AP view here, which is a fine view, but the only problem with it is if you look at the glenoid and the humeral head, they overlap a little bit. So you're not really seeing the joint, the glenohumeral joint in tangent on this view. There's another type of AP view called the Grashey view. In this case, you see the glenoid and the humeral head and they're not overlapping, so you actually see right down the glenohumeral joint, which is important to evaluate the alignment of the joint. There's also a trans-scapular, what we call a Y view. Now why do we call it a Y view? Well if you look at it, you can see the body of the scapula there in yellow, anteriorly you have the coracoid process, and posteriorly you have the scapular spine and acromion process. And that forms the letter Y. And you want to see your humeral head overlap that intersection where all those things meet. If you don't, like in this case you have the letter Y and the humeral head is posterior to the intersection of the various limbs of the letter Y, this is an example of a posterior dislocation on the Y or lateral view. What about three views? Three views are appropriate for the distal extremities, the fingers, hands and wrists, and the toes, feet and ankle. And as an example here, we have a frontal or AP view of the foot. If we look carefully, we don't really see much going on here, although I think some eagle-eye people may notice an abnormality. But if we look at the oblique view, what do we notice? Well we'd notice if we look really, really carefully, we have a little bit of an offset of the second metatarsal bone and the middle cuneiform. And this is the kind of thing you see with someone has a Lisfranc fracture dislocation. In fact the CT did in fact confirm this. So the oblique views really, really help us look at the tarsal- metatarsal joints in the foot. Four views are appropriate for the middle joints, what I consider the knee and the ankle. And if you look here, we have a lateral view. I showed you that AP view just went by it, the lateral view, the external oblique view of the knee and an internal oblique view of the knee. The only view is this one view, the internal oblique view of the knee which shows you in fact that there is a fracture of the tibial plateau. I know it probably doesn't project well here, but you have to trust me. There is a fracture, a subtle fracture of the tibial plateau. So for the middle joints, the knee and the elbow, I recommend getting those four views. What about the spine? The standard examination is going to consist of a lateral view as you see here, a frontal view as you see here, and an open-mouth odontoid view as you see here, for better visualization of the odontoid process of the dens. What you can also consider is getting two oblique views, and these are good for evaluation of the pedicles and also for the neural foramina to see if there might be any bony encroachment of the neural foramina which may be causing radicular symptoms. The lumbar spine we also tend to get five views. We get a frontal view as we see here, a lateral view, a cone-down lateral view for better visualization of the lumbosacral junction, and we also again get two obliques for what we consider-- for evaluation of what we call the Scottie dogs and also the facet joints. Now what do I mean by the Scottie dogs? Well if you look here at this close-up view, I'll outline the Scottie dogs there. The transverse process right here is the nose of the Scottie dogs, we have the eye, which is the pedicle, the super-articulary facet is the ear and the inter-articulary facet is the front paw. Now we don't just come up with these things because we sit in dark rooms all day and we like to imagine animals on the radiographs, there's actually somewhat of a reason here. If you at the Scottie dog, you see a collar on the neck of the Scottie dog. That is a defect or a fracture of the pars interarticularis, or the part that's between the super articular facet and the inferior articular facet, and that indicates a spondylyosis that we see most of the time in adolescents, particularly gymnasts, springboard divers, dancers. And also we can look at the Scottie dog for facet joint osteoarthritis. If you look at the green arrows, that points to a relatively normal facet where you have the paw of the Scottie dog above, and the ear of the Scottie dog below oriented correctly, with no sclerosis. As you go down, the red arrows show more and more sclerosis along the paw and ear or the facet joint of the Scottie dog. That indicates facet joint osteoarthritis. Another suggestion. If you're suspecting a fracture of a phalanx, either the finger or toe, then you want to consider ordering radiographs of the injured finger or toe, as opposed to radiographs of the entire hand or the foot. Now obviously if you have metacarpal fractures, it's a different story. But if you're really just looking at a phalanx fracture, please consider ordering just the finger or just the toe. It actually improves the detail and the diagnostic accuracy. As you see here on these two images, a frontal and an oblique view of the foot, we don't see any fracture. On this lateral view, we don't see any toe fracture either. Well the toes all overlap, so it's really hard to see a fracture. But if we get dedicated radiographs of the first toe, the technologist will remove the other toes, if you will, from the area of interest, and here we can actually see that there's a small avulsion fracture in this kick boxer, who had a small fracture off of his distal phalanx. Another suggestion. Weight-bearing views are going to be appropriate in certain circumstances if you want to evaluate alignment, osteoarthritis, or scoliosis. For example, here's a non-weight-bearing view of the knee. And we see there is some osteoarthritis, the medial compartment looks a little bit narrowed and some osteophytes and some sclerosis. But when we actually get a weight-bearing view, you can actually see how bad the arthritis is. It's really bone on bone apposition. And this is the same patient actually on the same day. What we do is we tend to get our weight-bearing views bilateral so we can compare from one to side, you kind of get a freebie of the other side and oftentimes you see osteoarthritis over there as well. Same thing in the foot, non-weight-bearing view here. We have some osteophyte formation in the mid foot, but you can see that our arch doesn't look too bad. But when you make it a weight-bearing view, we see we clearly have a flat foot deformity and can quantify that a little bit better. Final suggestion for radiographs. You want to consider ordering special views when appropriate, for example tangential patellar view which goes by a variety of names depending on how it's obtained, a sunrise, a skyline, or a merchant view where you can see the patellofemoral joint very nicely, an axial view or axiallary view of the shoulder shows our glenohumeral joints, good for looking at Bankart fractures and glenohumeral joint alignment. So I want to move on now and talk briefly about CT, or computer tomography. So with computer tomography you still use x-rays, you have an x-ray tube that rotates with detectors that rotates around the patient as the patient is moved through the scanner, and then you get computer-aided reconstructions of the body tissues that are displayed as thin slices. The advantages over conventional radiography is it presents internal structures without superimposition of overlying anatomy. So for example, here we can see fractures to the distal tibia and the fibula even though the patient has a cast on. And we have a little bit of difficulty seeing the fractures, of course, with a cast. The other thing is you can actually distinguish different tissues a lot better than you can on regular radiographs. So here's what we call a CT scan of the ankle with bone windows, where you can see the bone detail very nicely. And you can take the same data, just window and level it a little bit, and now you see the soft tissues a lot better. You see the Achilles tendon is very bright, the fat in front of the Achilles tendon is a little bit darker, and then the musculature is kind of in between. I like to illustrate this with a little vignette here. This is, if you remember back-- I believe it was in 2003-- at least those of you from Chicago, Sammy Sosa got in a little bit of trouble because he used a bat that was actually a corked bat. So he prior to that got his 500th home run, I believe this was that bat, and the Museum of Science and Industry asked us to take a look at it and make sure there's no cork in it. So we got a radiograph of the bat as you can see here. It's very homogeneous, very homogeneous texture to the bat. But that wasn't enough, we had to get CT of the bat. So now if you look at the bat in cross-section, you actually see the rings of the tree that were used to make the bat. And the triangle around it is just the casing that it was in. So of course at this point we had to do 2D reformats of the bat and 3D reformats of the bat, and we can confidently say that bat was not in fact corked. Now University of Chicago, we actually do use CT on patients, and we use it to evaluate a variety of things. Cortical bone, for example. Complex fractures. Here's an example of a complex fracture of the head of a talus. Anatomy of complex joints, joint alignment, loose bodies in the joints. These are all great applications for computer tomography. The disadvantages of computer tomography, it's certainly more expensive than radiographs. Metal or motion artifacts are a problem, although they are becoming less of an issue with newer scanners. CT is not as good as MRI for detecting subtle marrow or soft tissue pathology, and I'll show you some examples later with MRI. And it does involve ionizing radiation, as well. Here's an example of a patient who has a hip prosthesis in, and you can see the metal artifact resulting in these streaks that really make it difficult to look at the bones and surrounding soft tissues. So when should you order CT scan following radiographs? Well to confirm a fracture not seen in radiograph, the exception being that MRI is really better for looking at fractures of the proximal femur. To evaluate the degree of displacement of fractures or the extend of complex fractures that I just showed you, to confirm intra-articular loose bodies, some bony deformities such as tarsal coalition, some cortically-based lesions like osteoid osteoma, which is a tumor you might see occasionally but it's pretty common. And to confirm calcification in bone and soft tissue lesions, as well. Just as an example, here is a radiograph of the calcaneus Hard to see, much going on here, but if you're really astute, you might notice that there's a little bit of irregularity here along the base of the anterior process of the calcaneus. This is from Grey's Anatomy text here, you can see the anterior process. And then the CT scan shows the fracture a little bit better, as we can see here. And again, we can do a variety of different reformats in order to show that to its best advantage. So when should a CT scan be ordered without radiographs? Well basically one time that you should consider this is if you are suspecting an acute cervical spine fracture. If you're actually worried enough to image the patient, the patient should probably go straight to CT. Chances are he's going to head to CT anyway, and it turns out this is actually more time-effective and cost-effective. But this is assuming that you're using some sort of criteria, such as the Canadian C-spine rules for no imaging, or NEXUS criteria which will stratify patients into those who really are likely to have C-spine fracture and those who are not. So if you use those rules and you're going to image the patient and it's an acute setting, it's probably best to go straight to CT. I'm going to talk a fair amount about MRI at this point. Now MRI does not use ionizing radiation. It uses magnetic fields and radiofrequency pulses to obtain a reconstructed image. And the contrast between the different tissues is actually based on the number of protons in the tissues and the rate at which they recover from stimulation by radio pulse in the presence of magnetic fields. So that's all the physics we're going to talk about today. The advantages of MRI, it has excellent soft tissue contrast resolution. You can distinguish muscle from fat from meniscus from cartilage-- it's very good in that regard. Also an excellent depiction of marrow abnormalities. Better than CT as a general rule, and again there's no ionizing radiation. It's very useful for evaluating marrow edema or lesions. It could be used for evaluating the cartilage both with or without intra-articular contrast as I'll show you a little bit, and also tendons, ligaments and muscles. The disadvantages, relatively poor cortical detail. That's actually where CT will excel. CT will actually show you cortical issues better than MRI will. Cost, it is the most expensive of the imaging modalities I've been talking about today. Motion and metal artifacts can be a big deal. You see here's an MRI of the ankle, which shows a large black blob that obscures the calcaneus and that large black blob is just due to just a couple tiny little needle fragments there, which cause a lot of metal artifact. It is a relatively long exam, usually in the range of 30 to 45 minutes, even up to an hour for certain examinations, and some patients are going to be contraindicated due to various implants or claustrophobia. There is-- I don't know if this is in your handout out or not, but there's a nice website called www.mrisafety.com. You might want to write it down. You don't have to register for it, you just go right in. And you can look up implants to see whether they're safe on either 1.5 or 3 Tesla magnet. It also gives you summaries of groups of types of implants or foreign bodies, as well. So when should you order an MRI following radiographs? Well, to evaluate soft tissue structures such as ligaments, tendons and muscles. Cartilage, be it articular cartilage or fibrocartilage like meniscus or glenoid labrum. The spinal cord, in cases of neuropraxia or neurologic deficit, generally you get a CT first in those cases. To evaluate bone marrow, so for example it can exclude a fracture, particularly of the femoral neck but also of the scaphoid or distal radius. To confirm, evaluate or follow the extent of marrow abnormalities, be it stress fracture, bone contusions, infection, tumor, and also to search for osteochondral defects or other osseous cases of chronic pain. So some frequently asked questions I'm going to try to answer here. I get asked a lot, what is the difference between T1 and T2 weighted image? Well, it's simple, very, very complex physics. But what I can tell you is that T1 weighted images and T2 weighted images emphasize the brightness of different tissues. So here's an example of a pelvis MRI. Fat, as we see with the yellow arrow, is brighter than muscle, as we see with the red arrow, which in turn is brighter than fluid, as we see in the urinary bladder in this case. T1 weighted images are good for anatomy, not so hot for pathology however. Here's the T2 weighted image. In T2 weighted images fluid, like we see in the urinary bladder, is brighter than soft tissue, with the red arrow pointing to muscle, and especially if the image undergoes what we call fat suppression. And in this case the yellow arrow is pointing to fat that we've intentionally made dark in order to make fluid more conspicuous. And since pathology, be it trauma or tumor or infection leads to edema, and edema is fluid. It's going to be bright. So it will show you a tumor or a pathology-- in this case it is a tumor of the thigh-- much better than you would see it on a T1 weighted image, where you can barely make out the tumor at all. Now on both T1 and T2 weighted images, there are certain structures that are normally dark. And that includes the cortex of bone, as we see here, tendons-- I'm basically showing you the iliotibial band right there but you can consider it a tendon of the tensor fascia lata if you wanted to-- ligaments like the medial collateral ligament I'm outlining here, and fibrocartilage such as the menisci and the glenoid or acetabular labrum. Now increased signal intensity in these structures is generally bad. Here's an example of a sagittal image of the knee. I'm showing you here the anterior horn of the meniscus and the posterior horn of the meniscus. Notice that they look like nice black triangles, that's what you want your meniscus to look like, your normal meniscus to look like. Here's a different patient. The anterior horn looks like a nice, black triangle. The posterior horn, on the other hand, has what we call brightness or signal within it, linear signal that's extending right to the surface of the meniscus. This is what we look for when we're looking for a meniscal tear. So when do you suspect a soft tissue abnormality on MRI? Well if you see abnormal signal or brightness within the structure that should normally be dark-- for example you see that with meniscal tears, partial thickness tendon tears-- that means you have a problem. If you have actual discontinuity of a structure, which is typically seen with full thickness tendon tears, then you have an abnormality. Abnormal thickness of a structure, which is often seen with partial tendon tears or degenerative tendinosis and non-visualization of the structures often seen with complete ligament tears, and I'll show you examples of all of these here. So here's a normal MRI, showing the supraspinatus. It's a coronal oblique image, and the green arrows are showing the normal, dark supraspinatus tendon. There's a supraspinatus muscle as it inserts on the greater tuberosity of the humerus. There's a humeral head. This, on the other hand, is a T2 weighted image, and the red arrow-- the upper red arrow-- is showing the end of a supraspinatus tendon, and the lower red arrow is showing this white triangle. That white triangle is fluid that is separating the end of the supraspinatus tendon from its insertion on the humeral head. So this is a full thickness tear of the supraspinatus with a little bit of retraction. What I teach my residents early on is the Three Stooges approach to rotator cuff tears on MRI. And this uses a different oblique, it's an orthogonal plan, the sagittal oblique images. So here the normal rotator cuff looks like black hair on top of the humeral head with a supraspinatus at the 12 o'clock position. So if you have a full head of hair like Mo, that means you have a normal rotator cuff. That's a good thing. But if you have a bald spot on the top of the humeral head, like Larry, that indicates a full thickness tear of your supraspinatus tendon, although the subscapularis and the infraspinatus and teres minor are probably intact. However if you have no head of hair, like Curly, that means you have a massive rotator cuff tear of most if not all the rotator cuff tendon. One day I'm going to get in here no one's going to know who the Three Stooges are, but if you do this could be of use. And you can all see partial thickness tendon tears, as well, where you just have-- for example, here, a tear of the undersurface of the supraspinatus tendon does not go all the way through. So MRI is very good-- relatively good for looking at that as well. Here's an example of a normal Achilles tendon outlined by the green arrows. Looks like a nice black cord that is going from the soleus that you see up there down to the calcaneus. This is Achilles tendinosis. It doesn't look like a cord anymore, it's more fusiform in morphology. So this is what degenerative tendinosis is going to look like on MRI. Again, the tendon gets thicker. In the transverse plane, the normal Achilles tendon-- outlined in red there-- kind of looks like it's smiling at you. It has this concave or flat anterior border, whereas the abnormal Achilles tendon, you see down below it looks like it's screaming at you. It has this convex anterior border. So you can use a bunch of different imaging planes. Here's a sagittal image of in the knee. The yellow arrows point to the ACL, the green arrows point to PCL. A lot of the time you don't see these on the same image, but in this case you did because of the way that the patient was obliqued. Remember I said with ligament tears, a lot of times you just don't see the ligament. So the red arrows are pointing to where the ACL should be, but looks like this big, gray blob of mush right now, which is how we diagnose an ACL tear. Bone on MRI. Cortex is always dark, as we said before. Normal cortex. Marrow is usually similar in brightness to subcutaneous fat because, in adults, marrow is predominantly fatty. So it's going be bright on T1 weighted images as you see here. We'll compare it to the fat right underneath the patella. On T2 weighted images it's going to be a little bit darker, as we see here, but not as bright as fluid. And then if you do fat suppression, you can see the marrow is going to be very dark, just like the fat that you see elsewhere. So this helps us determine whether the bone is normal or abnormal. So if on T1 weighted images marrow is normally bright, then it's going to become dark when it's abnormal, so in this case you have the two arrows pointing to an intertrochanteric fracture going right across the femur there. And it's going to become bright on fat-suppressed T2 weighted images. So the opposite of what you'd expect with normal. So causes of abnormal marrow signal, I'm not going to talk about them all, we'll go through it a little bit more in the workshop if you're going to be there, but fractures, bone bruises, osteonecrosis, infection, tumor, just about anything can cause an abnormal marrow signal. Now do you have to specify which images you want? Generally no, the radiologist is going to do that for both MRI and CT. But the images that we will select will definitely depend on the history that you provide us and the pathology suspected. So some MRI protocols that are designed to look for injuries are certainly not designed to evaluate for tumor or osteomyelitis and vice versa. When should you order the examination with intravenous contrast? Actually for injury, pretty uncommonly. But for suspected tumor, infection, we do recommend it in most cases for things where you're looking for vascularity within the lesion. If you're uncertain, ask your radiologist. How about intra-articular contrast? When should you order with intra-articular contrast? Well if you've gone in to evaluate very small intra-articular structures, such the glenoid or acetabular labrum or the wrist ligaments, this is generally when we recommend that you order it with intra-articular contrast. Usually these are ordered by orthopedic surgeons or sports medicine specialists. Here's an example of a T2 weighted image of the shoulder, and the green arrows are pointing to the superior labrum. The superior labrum looks good on this image. When we take the same patient and we inject gadolinium you can see there's this tiny little linear focus of bright signal within it, and that's Gadolinium getting into a superior labral tear. And so that's why we do these studies with Gadolinium, to bring out these tears that you may not normally see. In the last few minutes, couple minutes, I'm going to talk about bone scan and ultrasound. Bone scan, very quickly-- what we do with bone scan is we inject a radiopharmaceutical, or tracer, intravenously that's absorbed by bone. And this tracer emits radiation that is then measured by a scintillation camera. The advantages, it is very sensitive for detecting bone pathology that results in either changes to regional blood flow to that bone, or osteoblastic activity. And the nice thing about bone scan is you can image the entire skeleton, as you see here. So on the left we have a normal skeleton, on the right we have a skeleton, a patient who has multiple skeletal metastases, and you can see this in multiple hotspots. It's very useful for evaluating metastases, that's the primary reason for getting a bone scan nowadays. You can also use it occasionally to look for reflex sympathetic dystrophy, occult trauma such as stress fracture and shin or thigh splints-- although we're moving really more and more toward MRI in those cases-- and osteomyelite is not seen on radigraphs, so again MRI is probably going to be better those cases. And what we see here is a lateral view of the leg showing a hotspot in the tibia that is a stress fracture of the tibia. The disadvantages, it takes awhile. You inject and you have to wait 2 to 4 hours before you can actually image the patient. It only grossly localizes the abnormality, it's not specific. Anything that causes increased uptake or blood flow-- tumor, infection, trauma-- will cause an increased uptake. Therefore oftentimes you're going to need additional imaging to look at the area of interest. Also in kids, the growth plates can normally be hot and obscure pathology. In this case, we see what looks like a relatively normal-looking bone scan. I don't think anyone would necessarily say that that shoulder, that proximal humerus, was any different than the other side. But if you look at the radiograph, he has a lytic lesion in the humerus which fortunately was benign and it actually has a fracture through, which the bone scan didn't even detect just because the normal growth plate is so hot on a bone scan. So for bone scans, we recommend for looking for metastases, determining whether a lesion is monostotic or polyostotic. Stress fractures, osteomyelitis, these things generally we'd go to MRI nowadays for, but occasionally we still use bone scan if MRI is contraindicated in that patient. RSD occasionally, but again remember that additional studies are going to be needed. So finally I'm going to talk about ultrasound. With ultrasound, a lot of people look at an ultrasound image and think it looks like this, and to me it does, too, sometimes. It uses high-frequency sound waves, so again no ionizing radiation with ultrasound, which is good. And images are provided-- produced-- by recording reflections or echoes of ultrasonic waves as they are directed into the body and then back to the transducer that you're holding. The advantages, it's a real-time dynamic evaluation of joint structures. I can actually look at an image of a tendon while I'm flexing the finger, extending the finger for example, or the shoulder. Easy comparison with the other side, you just flip it over to the other side. No ionizing radiation, it's relatively portable and relatively inexpensive compared to CT and MRI. The disadvantages, it's very operator-dependent. You have to know what you're doing. You want to make sure your technologist or your radiologists are familiar with the anatomy and how to use the ultrasound. And also bone is not well-visualized. Bone itself, cortical bone, will be a barrier to sound waves, so you can't really see the medullary space of bone, for example. So when do we get ultrasounds? Well to evaluate certain tendons like the rotator cuff or the ankle, certain intra-articular and peri-articular fluid collections and masses like popliteal cyst or aneurysm, and also in the infant hip to confirm or exclude developmental dysplasia of the hip. So on the image over here you see an intact tendon shown by the green arrows, and the disrupted tendon shown by the red arrow where, instead of having those nice little linear striations that make up the tendon, now it just disappears into a black void so to speak. And then the thin green arrows are showing the volar surface of the proximal phalanxes. This is actually a finger ultrasound that we're doing. And notice that, below that surface of the proximal phalanx, there is nothing. It's just black. Again that's because no sound is getting down there to give us any information. This is just an example of one we did relatively recently of an ultrasound of a rotator cuff, where I've outlined a humeral head, the greater tuberosity, supraspinatus tendon, and the overlying deltoid muscle. And you can see there the red arrow is pointing to a defect in the supraspinatus tendon that's quite similar to that MRI image that I showed you a little bit earlier. This is one of the Achilles tendon that we had a while back of the-- on the far left image, the green arrows are showing you a normal Achilles tendon down to the calcaneus. This is comparable to lateral view or a sagittal image on the radiograph. In the middle we don't really see much, but on the ultrasound image on the right the green arrow is going to the tendon up to the red arrow which shows a disruption of that Achilles tendon. This is just sort of interesting case, it's my last case here, showing a normal-looking foot radiograph, but they were very concerned about a stress fracture. We took a look on ultrasound, and the red arrows up there are pointing to a little bit of a periosteal reaction and hematoma along the metatarsal, and then a couple weeks later we confirmed the stress fracture. But we were able to pick it up basically right when the patient came in on ultrasound. So in summary, there are numerous imaging modalities. I know I talked quickly and tried to get to the major ones, and each of these may provide valuable information to you as a clinician. But obviously a good history and physical examination remain the cornerstones of diagnosis. Conventional radiographs generally should be ordered before other, more expensive tests, with a few exceptions, and if additional imaging is necessary, please consult your friendly radiologist to determine which test is best for your patient. And please also supply your friendly radiologist with pertinent clinical history or even a differential diagnosis when appropriate. And I thank you very much for your attention.