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32 TheHorse.com The horse April 2015 want to assess the bone associated with the soft tissue." On the other hand, says Kent Allen, DVM, of Virginia Equine Imaging, in The Plains, while radiographs are useful for detecting bony conditions, they are less sensitive than some other modalities. "You can have tremendous inflammatory change going on within the bone, and the radiographs can still look completely nor - mal," he notes. "You can have a problem, and yet the radiographs are not going to reflect that problem for 14 to 21 days." Barrett echoes the sentiment that while radiography has its place, it's not the most sensitive tool out there. "The downside to radiographs is that by the time we see secondary osseous abnormalities—bone changes associated with osteoarthritis—generally there is already much more disease in the joint than we have any idea of because we can't see cartilage, joint capsule, and synovium (joint lining)." In addition, Barrett notes that not all digital radiography is up to snuff: "If you don't have a good system, there will be limitations in interpretation." Computed Tomography (CT) Often used to detect dental, sinus, and spinal issues, a standing CT scan pro - duces 1-3 mm cross-sectional images of an area in a sedated horse. "We get much more information from a skull CT than we do from radiographs because there are many structures (in the horse's head that are difficult to distinguish on X rays)," Barrett says. "Also, being able to now im - age the standing cervical spine (the neck) is an exciting frontier." Practitioners can also use CT to image limbs. "In terms of the foot and joints, there's a lot that has been published about looking at the deep flexor tendon injuries with CT using radiocontrast agents; the contrast tells us about the vascularity (blood supply) of lesions," says Barrett. "CT is excellent for bone—it's the best way to evaluate fractures." Further CT options are on the horizon, notes Allen. "There is new technology being developed for standing CT of distal (lower) limbs, which may change how we view imaging the limbs," he says. Magnetic resonance Imaging (MrI) With MRI, magnetic fields produce 3-D cross-sectional images, providing high- quality detail of both bone and soft tissue. Standing MRI, performed under seda - tion, captures images of the lower limbs. Recumbent (taken while lying down) MRI, which requires general anesthesia, offers a look at a greater anatomical range. "What we need to think about when we do an MRI is what structures are we are most worried about, as we have the op - tion of (from most to least detailed) high- field anesthetized, low-field anesthetized, and low-field standing MRI," Barrett says. "If I am worried about a joint in particular, I think it may be worth it to go straight to high-field MRI —you get a lot more bone and soft-tissue information. It allows us to see structures, especially in the hoof, that are otherwise difficult to see; it's the only reasonable way to look for bone edema (fluid swelling) and con - tusions. Low-field MRI has its limitations; to scan for subtleties, smaller lesions, or any type of articular cartilage damage, you need high-field MRI." Nevertheless, low-field MRI is often a reliable, real-world choice. "The majority of MRIs done are low-field standing," Al - len says. "These do a good job of imag- ing the foot in particular and to a lesser extent structures above the foot and subtleties." They also don't come with the same anesthesia risks—such as stress to the body, injury during recovery, or other complications—as the other options. "MRI is unusual amongst imaging modalities because it is both sensitive and specific," Allen adds, meaning it of - fers few false negatives and positives. "It's also unique in that you can see both soft Diagnostic Imaging 101 Veterinarians rely on radiographs extensively for prepurchase and lameness exams. AnimalImaging visibly better www.animalimaging.net A C V R D I P L O M AT E O F V E T E R I N A R Y R A D I O L O G Y • A M E R I C A N C O L L E G E • 6112 Riverside Dr | Irving TX 75039 (972) 869-2180 Look to Animal Imaging if you have an equine or small animal patent that can beneft from our advanced technology, expert board certfed radiologists and personal service. • MRI - 3 Tesla - for unsurpassed image quality and faster acquisiton tme • CT - Standing CT for the equine • Scintgraphy - Bone Scans • Radiology - Digital plate for imaging large areas of anatomy (back, pelvis, etc.) • Teleradiology • Ultrasound - Performed by highly trained board certified equine radiologists Kevin THompson/THe Horse