• LecturehallThe Radiology Podiatry Toolbox-Overview of Imaging Modalities
  • Lecture Transcript
  • TAPE STARTS – [00:00]

    Marlena Jbara: Hi, my name is Marlena Jbara and in this section, we will be discussing radiology podiatry toolbox and overview of the imaging modalities. I or related party have no financial relationship to disclose. So the objectives of this talk is to review what's in the toolbox, we will review when that tool or imaging modality is indicated and then we can review the limitations of these tools. And the tools that I'm talking about are plane radiographs, ultrasound, computed tomography or CT, magnetic resonance imaging or MRI, nuclear scintigraphy and PET scanning. The musculoskeletal imaging toolbox which contains the plane radiographs, nuclear medicine, ultrasound, CT, MRI and PET has given way to many advantages in imaging which can lead to a lot of confusion and we are going to spend the next few minutes sorting this out. Plane radiographs, they are widely available, reproducible. These are patient friendly exams. They are familiar with them. They are inexpensive and they are usually indicated at the primary imaging modality. And here we can see a lateral and frontal radiograph demonstrating the typical talar joint, the subtalar articulations, whether or not there is ankle effusion. We can see on the frontal radiograph relationships between the hallux metatarsal and phalange with hallux vagus deformity, rotation of these fibular sesamoids. And when looking at x-rays, we are looking at different planar imaging.


    So we can use our standard imaging planes, cutting the body in the coronal plane as if you are putting a crown over your head, in the sagittal plane sort of splitting you in half and open booking you and looking at you from the sides. The axial plane being the transverse plane cutting you sort of like a pepperoni and slicing. We can look at medial and lateral extents, cranial and caudal extents and proximal and distal relationships from looking at x-rays. Furthermore, x-rays provide standard radiographic protocols where by imaging the x-ray in the same angular momentum, we can draw relationship and create a hypothesis about the biomechanics of the foot. So when we are looking to consider pathology in a certain area, we will image the area of question and we are going to image it usually in three views. So just obtaining a single view or even sometimes two views may not be enough to see all of the pathology and supplemental views may be indicated in certain circumstances. It's important to understand the anatomy of a bone. So basically at the top, I have the humerus and this is created from a spongy bone that's making up the medullary canal with more compact bone creating the cortex layered with periosteum wrapping the entire structure. The marrow cavity is a bioactive community of producing white and red blood cells and marrow activity. Moving to the illustration at the bottom left, this is an illustration of pediatric bone where you can see the epiphysis, the metaphysis and the diaphysis. A nutrient vessel will enter the diaphysis. They will head towards the metaphysis where slower flow will sludge through the sinusoids.


    This may be an area where infection can occur because of the slow flowing blood. There is a physis which is the zone of regenerating or generating osteocytes and we have the epiphysis which does not add length to the bone but it adds an articular surface and in the infant we do have these epiphyseal vessels which obliterate within a couple of months of life. So in the long bones, we can have the diaphysis, the epiphysis and the metaphysis covered by layers of articular cartilage and periosteum enveloping a medullary or marrow cavity. On x-rays, we can see types of joints. The functional classification is the synarthrosis which is an immovable joint, the sutures, the teeth and the epiphysis. The amphiarthrosis which is the slightly movable joint which is usually like the distal articulation of the tibia and fibula between the intervertebral discs, intervertebral bodies and even between the cuneiforms. These are amphiarthrosis. And diarthrosis are freely movable joints. They are synovial line joints. This is likely phalangeal joint and these are freely movable, usually in at least superior to inferior but sometimes a small amount of adduction and abduction is functional at these articulations. When we are forming an approach to radiology, the blackest thing on the picture will represent air. Then the fat density will be dark gray. Soft tissue in general will be gray. The bones of course because it has calcium which absorbs more than soft tissue, they will look white. And foreign bodies will depend on what the foreign body is made of.


    So metals will be extremely dense and seen on an x-ray. They absorb the x-ray depending on the thickness and its anatomic number and you will be able to see it. In this case, what you are seeing is gas, emphysematous change and necrotizing infection in a patient who has osteomyelitis with the erosion of the hallux proximal phalangeal stump. I think it's important to understand the terms and use them in your report in radiology with radiopaque being more dense, radiolucent being more transparent and factors that affect those appearances are important for you to ascertain on the x-ray whether it's the density in composition, the thickness of the tissues, the summation of all the x-ray shadows and technical factors such as kilovoltage and time of exposure will affect what the image eventually comes to look like. Of course, this is our work course in the emergency room to develop working differential diagnosis for patients coming in with pain here is a normal x-ray of the ankle where you can see the normal lateral tibial fibular clear space and that's 1 cm from the tibial plafond to the edge of the fibula and that should be no more than 4 mm. We have the medial clear space which represents where the deltoid ligament which is when it's intact measures about as equal to the lateral clear space. We can see the ankle mortise. We can also assess whether there would be effusion based on the tear drop sign here if there would be a robust distention of the joint capsule. We can see subtalar anatomy, the anterior calcaneal process, even portions of the sustentaculum talus. Looking through the calcaneus, we can see the position of the fibular which is going to be important in understanding biomechanics including pes cavus.


    Again, more ankle anatomy. Notice, you can see the cortical bone, the medullary bone, the joint space of the articular surface with exquisite detail. We can also talk about alignment on weightbearing x-rays here as a frontal and oblique x-ray. In general, joint should have congruency to articular surface. They should line up with one another. Subluxation is defined as partial movement of the smaller body parts on the larger body part where dislocation is complete lack of joint congruency between two articular surfaces. X-rays can give us a chance to talk about types of fractures where common types of fractures can be transverse. We can move on to spiral or oblique fractures. Comminuted meaning more than three pieces and segmental being three pieces where one is free floating fragment. In addition, we can talk about alignment, whether it's angulated with respect to one another fragment or straighten. We can talk about open versus closed fractures where in an open fracture, the skin is lacerated and this is going to give risk for infection where in closed fracture, there may be no laceration. Furthermore, you can see lucencies within bone. You can see tumors whether they are benign or malignant. In this case, you can see this subarticular lucent lesion which is a chondroblastoma. We can also assess for osteomyelitis and of course obtaining the history is going to be key. Here is a nice example of osteomyelitis where the earliest finding may be osteopenia. Then you may have resorption of cortex, osseous destruction followed by pathologic fracture can be seen here. It may spread to the adjacent joint space as seen here with septic arthritis and pathologic fracture.


    Bony structures can demonstrate diffuse lucency as seen in osteoporosis where in this case you can see cortical thickening along the second metatarsal stress fracture that this patient has endured. Of course, you can see increased opacity or sclerosis. In this case, this is Ewing's sarcoma with diaphyseal sclerosis replacing the fifth metatarsal. But you can also see reactive bone sclerosis with bone production from fractures, tumors, infection. Of course, osteoarthritis with subchondral sclerosis but in this case of course Ewing's sarcoma. Furthermore, we can make assumptions about the cartilage by identifying bone fragments along the subarticular surface which indicate that there is an osteochondral injury. We may see chondrocalcinosis at the joint space which is deposition of calcium pyrophosphate crystals and hyaline cartilage and fibrocartilage. X-rays give us the ability to characterize arthritis whether it be degenerative where there is osteophytes, asymmetric joint space narrowing at the DIP and PIP joints. This is the most common arthritis affecting us today. An arthritis can be further characterize into different types. In this case, this is psoriatic arthritis, but we can see rheumatoid arthritis which is the inflammatory arthropathy of unknown etiology characterized by synovial inflammation, pannus formation and erosion formation.


    Findings here include erosion, symmetric joint space narrowing, whiskering or periosteal new bone formation. In the feet, we can also see hydroxyapatite disease and chondrocalcinosis. And you can see this along the third DIP joint, this calcium production. Also note at the hallux MTP, there is additional calcium production and this was in my nurse manager who had a painful red toe for months and still does and causes her lots of grief. So it can be a debilitating disease. And I would like to offer a differential diagnosis. Generally, when I'm looking at x-rays, I'm thinking about VINDICATE which could be osteonecrosis, infection, neoplasms where the drugs are involved and steroids are implicated in osteonecrosis. There can be inflammatory conditions, congenital etiologies for disease, autoimmune where there would be rheumatoid arthritis or ankylosing spondylitis, trauma, of course fractures and dislocation and endocrine disorders, metabolic disorders including Paget's and hyperparathyroidism as seen in renal osteodystrophy and of course gout. Moving on to ultrasound, this is an amazing modality because there is no radiation. It's reproducible in trained hands and it's excellent for superficial soft tissue elements including tendons and muscles and it can be patient friendly. There is a small to moderate expense relative to MRI and cross-sectional imaging. In ultrasound, there is a routine exam room which is equipped with adequate imaging devices to image a host of depth. We use a superficial gel which can be standard or it can also be sterile.


    And you basically apply this to the transducer and apply it to the patient and that intervening gel creates space for the piezoelectric spinning crystal within the transducer to produce sound waves that penetrate the patient, that touches the patient's organs and certain amount would be reverberated back to the transducer allowing for visualization of the structure. So it can be a static exam in that way. We can also identify vascularity through Doppler assessment and we can also perform dynamic imaging. It's possible for us to invert and evert the foot and assess the peroneal tendons at the retromalleolar groove. Of course, we can do a Lachman's maneuver and look at plantar plate instability. We can do Mulder's maneuver for your unhappy patients who have large Morton's neuromas that hurt them. Ultrasound. And here is an example of how that works. Basically, we can see that the ultrasonographer sits where it's adjacent to the patient. They can view the screen. You have foot and ankle radiology. We use a lot of hockey transducer imaging which is basically a 1-inch foot print on a very high frequency probe. The higher the frequency, the more resolution in the near field and the lower the frequency, the more resolution in the deeper fields. And here you can see how ultrasound can lend itself to imaging the superficial body parts with exquisite spatial resolution and we are seeing the intervening fibrils within the Achilles tendon as it attaches on the posterior calcaneus.


    If there were to be a retrocalcaneal bursa, we could see it here and we can see this with an exquisite detail so that if there were to be disruption of the fibrils or expansion or tendinosis or tears, we could clearly see that with reliability at the superficial body part. And we can use ultrasound in any superficial part of the body. So in this case, I'm giving you an example of Osgood Schlatter disease where there is thickening at the origin of the patellar tendon as seen in jumper's knee and here is the x-ray correlate demonstrating the soft tissue swelling. Moving on to computed tomography or CT, this is also widely available. It's reproducible though radiation is your cost here. It gives you an excellent bone assessment. You can see erosion and small changes within the cortical bone. It's occasionally used for soft tissue assessment if there is mineralization or density changes. It's a patient friendly exam. It goes quickly. It's associated with moderate expense. Of course, you can perform intervention on the machine, so this has a lot of power in terms of making the diagnosis and also providing therapeutic treatment. And nowadays -- it used to be that the metal created such big artifacts within the machine that you really couldn't use it but now we have improved our scanners and technology has advanced and we have metal reduction protocols. In computed tomography, this is usually a supine axial exam with some alternative position options. We can develop reformatted images after the exam for alternative views and the imaging time can be in seconds. It's never minutes these days.


    It can be with or without IV or oral contrast and in the foot and ankle of course, there is no oral contrast, but we also generally don't use IV contrast unless it's indicated for specific reason. And here is an example of what it looks like to go through a CAT scan. You go through a small aperture in the machine. The technologist slide you into position and then goes back to his work station where he will begin the protocol of this exam which will have a certain slice thickness, a certain KV and mAs and all those parameters will be controlled by the technologist with processes within the machine to modulate the entire dose to make sure that it is within physiologic range. And with CT, you can see small cortical changes. You can see fragments as seen in this case of a Lisfranc fracture dislocation. We can see on the x-ray that there is malalignment between the medial cuneiform and the base of the second metatarsal. And furthermore, you can see that fleck on the middle image best. Obviously, the opposite left normal side for comparison is your far right image. We can see bony anomalies. In this case, we are looking at subtalar degenerative changes. Here, we are looking at posterior subtalar degenerative changes within an enlarged os trigonum. And of course, we can see the abnormal articulation of the middle facet and sustentaculum talus giving us version of the drunken waiter sign as seen in fibrous coalition.


    And moving on to my favorite magnetic resonance imaging. This is widely available. It's reproducible. It's excellent for soft tissue pathology. It's also very good for bone pathology. It's not necessarily patient friendly in that the exam still takes about 15 to 20 minutes and patient can move which may degrade the image. It's associated with the larger expense. Absolute contraindication used to include cardiac pacemakers but now we have MR conditional cardiac pacing system. Electronic stimulators, those also used to be absolute contraindication and now we may turn off the battery pack and there may be protective measures that are applied. Foreign metallic bodies in the orbit are still an issue as these foreign bodies can move and create episodes of blindness. Obviously, if the body habitus can't fit in within the gantry, the patient cannot be imaged. And there is a huge listing maintained in every MRI facility. So if you have any questions, what you want to do is call your radiologist, call your facility and ask specifically. In addition, getting this much information from the patient as possible to what implantable device they have, whether or not it has a serial number will be important. There is going to be a website that you can go to, MR safety and that is maintained and updated regularly. In MRI, the patient is usually performed supine. There is a multiplanar imaging obtained without the person changing their position. One exam is one area. So in the foot and ankle, the ankle is one area. That's also the same thing as the hind foot. The midfoot is another area and the fore foot is the last area. And generally, these are not scanned together. Occasionally, we can scan the mid to fore foot together, but depending on the size of the foot, you may not get the optimized soft tissue contrast.


    The average exam time again is 20 to 30 minute and there are strict guidelines for sedation. And if you have any question as to how to order the exam, you want to ask the radiologist. This is their field. They are trained and developed to answer all of these questions and they will be able to provide a protocol for any clinical questions that comes on the board. There are open options where the magnetic bore is both above and below you rather than circularly as in the closed bore. Patients like the open bore and that those that are claustrophobic may be able to move their arms and sit at the sides where in the close magnet, there is a complete loop around you. So generally speaking for the foot and ankle, your head is not all the way in the center of the machine, so a lot of people do not experience claustrophobia. And of course, I insist on the closed magnet for its superior resolution, but there are newer scanners that are absolutely excellent that are 1 Tesla open magnet. So it really depends on the machinery that is available to you as to what is best, whether it be open or closed. MRI is the work course for demonstrating the changes related to talar dome osteochondral injuries. We can see bone marrow edema seen here under the lateral talar dome. We can see the presence of unstable fragments and whether or not fluids get beneath them to determine stability. Again, we can see bone contusion, microtrabecular fractures as seen here in the left sided digit. Sagittal T1 weighted image demonstrating hypointense change, T2 weighted image demonstrating hyperintense change. Notice this curvilinear hypointense both on T1 and T2 linear signal and that you can barely see this on the x-ray below. So there is going to be an earlier indication of disease on the MRI that you are going to be able to accurately reflect that may not be seen on the x-ray.


    Of course, we can use this for gout looking at these nodular foci surrounding the hallux MT. Here you can see on the dorsal image along the second MTP and these are the tophaceous gout, basically balls of uric acid crystals creating erosions along the bone. MRI is our work course for infection, particularly osteomyelitis. In this case, we had a lucent lesion within the cuboid with surrounding patchy sclerosis identified in the x-ray and we can see on the MRI the left-sided coronal or long axis T1 weighted image demonstrating isointense signal changes to skeletal muscles with irregularity replacing the normal marrow fat. And in this case on the long axis T2 weighted image, notice the heterogeneous elevated T2 signal most bright within the center of the abscess. And of course, we drained -- that was a Brodie's abscess of the cubiod and you can see a needle penetrating to the thickened cortex of the subacute osteomyelitis. We can also image common bone tumors. In this case, this image on the right is an older image of an osteoid osteoma within the talar neck. But we can see many common bone tumors, NOFs, giant cell tumors, aneurysmal bone cysts, of course simple bone cyst and lipomas in the calcaneus and in this case, again the osteoid osteoma. A nice example of plantar fibromatosis where you see the short axis T1 weighted image demonstrating an isointense or hypointense nodule related to the plantar fascia, barely seen on the short axis T2 imaging, plantar fibromatosis.


    I have included a nice example of the os trigonum syndrome. There is ossicle at the posterior aspect of the ankle implicated in dancers, football player, anyone on points and demonstrating the elevated T2 signal in a person who has pain at the posterior ankle, posterior impingement. Of course, we can see foreign bodies here as a piece of wood at the plantar aspect of the foot surrounded by hypointense signal along the second to third metatarsal interspace, foreign body exquisitely seen. Of course, this would most likely be seen in all modalities given the size of inflammation. Moving on to nuclear medicine, this is excellent for specific pathologies in the right hand. We can diagnose osteomyelitis and specially using it for infected hardware. Nowadays, I begin my osteomyelitis inspection with MRI and of course x-rays and MRI. The work course for me in nuclear medicine would be looking at infected hardware. Metastasis, not necessarily multiple myeloma but bone scan is excellent to determine the presence of metastasis. We can look for occult fractures and it has a strong negative predictive value and is usually normal and that's the power of this study. If it's normal, there will not be disease there. Generally, in nuclear medicine, we use -- for the bone area, we are going to use an injection of radioisotope technetium bound to phosphate. We can also use Indium labeled WBC to increase specificity and infection. We can provide delayed static images with the superficial detector to increase the number of counts and specificity. And the best usages are for infected prosthesis and localizing infection or fever of unknown origin.


    An example of nuclear scintigraphy, the three-phase bone scan, we have the angiographic phase which is the blood phase and that's performed immediately after radiopharmaceutical injection at 1 to 2 second intervals for about 32 to 64 frames and we can see here the distal aorta, the bilateral iliac system coming down towards the legs in this angiographic phase. This is followed by the blood pool phase where static images are immediately obtained and the tissue phase, the blood pool phase you can see here. In nuclear scintigraphy, we have a three-phase bone scan, the delayed phase images, we can see here about two hours later and furthermore delayed phase imaging you can see on this three-phase bone scan. Here is a nice example of osteomyelitis in a 9-year-old boy who presented with pain in his right foot. The pain had been present for five days before imaging and note the increased uptake at the medial and lateral aspects of the right ankle both seen on the anterior and medial and lateral imaging, asymmetric to the left side. And lastly, moving on to FDG-PET, FDG-PET represents essentially the situation where we are going to draw the patient's blood and then we are going to mix it with an activated fluorodeoxyglucose and we are going to inject that back in to the patient and the inflammatory cells within your body preferentially metabolize the glucose.


    And we would then image that. We would take an anatomic image using CAT scan and fuse that with the physiologic fluorodeoxyglucose imaging and we would get this PET scan which is a fused image. And when we compare that in terms of osteomyelitis to using bone scan or Indium- 111 or technetium labeled WBCs, we see that it's probably the most specific and sensitive but also the most expensive that we have. So generally speaking, this is not widely used but I do present it because it is being used in some institutions. And the power of FDG-PET is that the SUV may differentiate the Charcot foot from Charcot plus osteomyelitis and really can also give us an accurate assessment of metal implants. And when we look at the comparison of the efficacy of the FDG-PET to other modalities, we can see that comparing MRI to FDG-PET, the specificity of FDG-PET is much higher, 93%. That means that if the disease is present, it will be picked up. And so this portends that the PET would be very useful. In the future, the price of course would come down and availability would be provided. In summary, we have looked at x-rays, ultrasound looking at the lack of radiation, the operator dependency, the dynamic capabilities and the intervention possible in real time. We have touched on CT for spatial resolution, alignment, a quick survey for fractures and of course soft tissue gas, emphysema. In MRI, we have looked at soft tissue contrast, infection, tumor. We have looked at occult trauma. In nuclear medicine, we have discussed bone scans, the three-phase bone scan. And of course, lastly, we touched on the power of the PET imaging that it's specificity is higher than MR but not widely available and extremely expensive, so not the work course currently in osteomyelitis. And lastly, I want to just leave you with knowing and consulting your radiologist for the use of contrast. I think a phone call to the radiologist regarding any kind of implantable device is warranted and your radiologist will be happy to serve you and let you know what is best for imaging of your patient. I thank you for your generous time and attention and hope this lecture has been of value for you.

    TAPE ENDS - [32:50]