EQUINE AND LARGE ANIMAL RADIOGRAPHY CH 24.

Pedal Bone/P3/CoffinDP.

High coronary view courtesy of Seneca College, Veterinary Technician Program, King City, ON High coronary view: Dorsal 65-degree proximal-palmarodistal oblique (D65Pr-PaDiO). The beam is angled to the ground 65 degrees dorsoproximal (stand-on route) (see Figure 26-8). The foot is on top of the cassette tunnel, which is placed on the ground. The foot is placed near the center, and the toe close to the front edge of the tunnel. Upright pedal route: Dorsoproximal-palmarodistal oblique (DPr-PaDiO). The beam is horizontal and parallel to the ground with the toe pointed down . Point the toe of the foot downward so it is resting on a block or a navicular block is used. The sole is perpendicular to the ground, and the dorsal hoof wall is 45 degrees from the horizontal. For the coffin bone. True Dorsopalmar view: Dorsoproximal-palmarodistal (DPr-PaDi; Figure 26-9B). The beam is horizontal and parallel to the ground, but the foot is weight-bearing. The foot is placed on the wooden block to raise it to the level of the x-ray tube. The image receptor is positioned vertically and directly caudal to the foot on the floor or in the cassette groove. Central Ray and Collimation Center on the midsagittal plane of the pedal bone (dorsal foot wall) just distal to the coronary band. Include the full digit—foot wall, pedal bone, superimposed navicular bone, middle phalanx (P2), and the distal part of the proximal phalanx (P1). Collimate, include labels and borders are visible. Comments ( also applies to the hind limb) •Aim the central ray at right angles to the correctly trimmed foot wall. •Lift the opposite limb for restraint for the high coronary view. •Proper full preparation of the sole is essential. •Wings of the coffin bone and distal sesamoids should be equidistant. •The purpose of the high coronary study is to note the number, size, and character of the vascular channels. The crena, which is the large notch in the solar border, the palmar processes or wings formed by the solar border, and the angular or collateral cartilages are all noted.3 This is the preferred view. •The upright pedal route better shows the extensor process, conformation, quality of hoof care, and relationship of foot to the surface 3 •The study with the foot weight-bearing and the beam parallel to the ground is slightly more limited than the high coronary view but does assess lateromedial foot imbalance, some distal phalanx fractures, and ossification of the collateral cartilages of P3.2.

Equipment.

Photographs courtesy of Seneca College, Veterinary Technician Program, King City, ON Equipment •Of the three types of x-ray machines available—portable, mobile, and ceiling-mounted—the portable unit is the most practical for those in ambulatory practices. •Portable units are small and can be set up wherever there is a power supply. •kVp and mA-generally preset, range 40 to 120 kVp and 15 to 100 mA. •Time is usually the variable control -mAs values of 0.3 to 100. •Newer units have variable kV and mAs. •The maximum mA is usually 30 - 50 and the max kV usually 60 - 100 •Digital displays allow adjustments of 1 kV to 5 kV increments •These units are generally adequate for radiography of the equine distal limbs, skull, and cranial cervical vertebrae. •Disadvantages of these units are the relatively low mA capacity, making movement more of a concern. •Line voltage may also vary, causing inconsistency in the exposures. •It may be difficult to see the field of collimation in well-lit areas leading to increased radiation to personnel •Although the portable equipment is built to withstand a certain amount of rough handling, transportation and frequent movement of radiographic equipment increase the opportunity for damage to x-ray equipment. • The unit should never be left in the vehicle overnight during below freezing temperatures unless a sufficient warm up time is taken into consideration prior to the first exposure. •Mobile units can be wheeled from room to room in the same premises, but they are generally too cumbersome to be easily moved and transported. •The kVp and mA capacity is higher,- shorter exposure times , less chance of blurring. •Veterinary specialty referral practices commonly use large permanently mounted ceiling units on a set of ceiling rails to allow horizontal and vertical movement. •It may be difficult to obtain parallel views of the feet because the unit may not reach the ground close enough to prevent obliquity though a supplementary portable unit is often used in these situations. •These high capacity units have the greatest output range (between 800 to 1000 mA) capable of obtaining good quality radiographs of regions such as the chest, pelvis and thoracolumbar vertebrae. •Regular maintenance and calibration of the x-ray unit s are essential to the production of quality radiographs and maintenance of a safe working environment. Inspections should be implemented as per local regulations. •See Chapter 9 for further information on digital equipment

Radiation Safety and Positioning Devices.

Photographs courtesy of Seneca College, Veterinary Technician Program, King City, ON •All of the radiation safety principles applied to small animals also apply. •When working with large animals, concern for physical safety often supersedes radiation concerns. •It is essential to keep the three tenets of radiation safety in mind (shielding, distance, and time). •Portable machines,-can be particularly dangerous with regards to radiation exposure. •Aimed in any direction, and longer exposure times to produce diagnostic images. •Caution must be taken to ensure no one is in the path of the primary beam. •It is critical to wear a lead apron and gloves when holding the portable radiograph machine.1 •If in the path of the beam -must have appropriate protective lead attire and a radiation dosimeter. •Personal protective equipment (PPE) -routine maintenance schedule to evaluate weaknesses and breakage. •Proper storage of PPE is important; avoid folding gowns and gloves. •Protective wear can shift. •Proper fitting and positioning of protective gear must be made at all times. •Most important is to increase distance from the primary beam through the use of a cassette holder . •Avoid holding image receptors directly in your hand. •Need a positioning block to raise the affected foot. •Especially true for the lateromedial view of the foot. •A cassette tunnel -for digit radiographs to protect the image receptors for DP/oblique oblique views of the foot. •Purchased or manufactured out of radiolucent wood (avoid use of nails) or hard plastic. •Make sure that the primary beam is collimated to include only the area of interest. • All margins of the primary beam should be visible on the processed film. •For horizontal beam -conscious of where the beam is directed. •To help decrease exposure time, use a fast combination of film and screen. •SID is generally less for large animals,- 26 to 30 inches, compared with 40 inches •This factor also helps decrease the exposure time.

Comparison of Human and Equine Skeleton.

TECHNICIAN NOTES •A human middle finger is equivalent to the front foot of the horse, whereas the hind foot is basically a human's middle toe. •It is no wonder the foot is the most frequently imaged for lameness issues.

Equine Radiographic Anatomy.

•Dorsal, palmar and plantar, cranial, and caudal: •Remember these terms take precedence when combined with other terms. •From point of entrance of the beam to point of exit is how radiographic projections should be described. •Terminology of the limbs proximal to the tarsus and carpus: •Cranial (the part of the body facing the head). •Caudal (the part of the body facing the tail). •Distal to and including the carpus and tarsus: •Terms are dorsal (the part of the body facing the head). •Palmar (front limb facing the tail) or plantar (hind limb facing the tail). •Oblique: •Not parallel to one of the two major directional axes in the introductory positioning chapter. Tangential" or "skyline" • In a direction perpendicular to the line of sight. It is the plane that "just touches" the surface at that point (from Latin tangere, "to touch").

Labeling and Terminology.

•Markers placed laterally and dorsally (or cranially) •For the dorsolateral-palmaromedial oblique (DLPMO) view, the central ray faces the dorsal part of the limb aimed 45 degrees laterally from the midline. •The image receptor is on the palmaromedial aspect of the limb so that it is perpendicular to the beam. •Remember "point of entry to point of exit"; the beam travels from dorsolateral to palmaromedial. •The film marker is placed along the lateral aspect of the image receptor and appears to be along the palmar aspect of the limb in the radiograph. •Proper description for this 45-degree DLPMO view is dorsoproximal lateral 45-degree-palmarodistomedial oblique (DPrL45-PaMO). •What is actually being highlighted on this oblique projection is the opposite bone that is being radiographed, specifically the lateral portion. To be more technical, specifically, it is the dorsomedial and palmarolateral surfaces of the limb (red lines on Figure 26-6). This might seem confusing because it is the surface opposite to the name of the view. But keep in mind that the side that is closer to the film will be hidden behind the bone, allowing the projection farther from the film to be in profile. •For the dorsomedial-palmarolateral oblique (DMPLO) view, the central ray is aimed at the dorsal part of the limb 45 degrees medially to the midline. •The image receptor is on the palmarolateral aspect of the limb and is perpendicular to the beam. •The beam is traveling from dorsomedial (point of entry) to palmarolateral (point of exit). •The film marker is placed along the lateral aspect of the image receptor , appearing to be on the dorsal part of the limb in the radiograph. Proper description for this 45-degree DMPLO is dorsoproximal medial 45-degree-palmarodistolateral oblique (DPrM45-PaLO).

Restraint and Patient Preparation.

•Proper patient preparation is essential •Easily become startled when confronted with unfamiliar objects, so it is important to minimize sudden movements and loud noises. •Movement artifacts, poor positioning of the patient or the x-ray beam, and inadequate exposure are the most common reasons that radiographs must be repeated. •Repetition also means further radiation dose for the restrainer or the patient. •Large animals in the standing position are minimally restrained- concern for human and machine safety. •Sedation can help calm the animal and curtail startling it to help diminish movement blur. •Keep the behavior of the particular patient in mind, modify your restraint to take advantage behavior. •Depending on the patient, consider: •Raising the opposite limb, using a twitch, offering food, or using stocks, among other strategies. •To help minimize repeat radiographs, take the time to make sure that the patient is properly positioned, the image receptor is properly placed, and the central ray is properly directed. •Debris such as shavings, mud, sand, small stones, and manure may cause radiographic artifacts. •Visually inspect and clean the legs and hooves well before performing radiographs. •The hair coat should be dry, brushed, and cleared of dirt or other debris. •If the foot is being radiographed: •Important to prevent overlying shadows superimposed on the field of view- DP/ oblique •Remove the shoe and trim back any overgrown portions of the foot. •Pick, thoroughly clean the sole and clefts, pack the sulci adjacent to and in the center of the frog -Play-Doh, methylcellulose, or softened soap-eliminate gas shadows caused by grooves of frog . TECHNICIAN NOTES •A piece of paper, plastic wrap, paper towel, or dry gauze is suitable to keep the packing material from picking up particles. •If film cassettes are used and radiographs are being taken off site, make sure to take enough cassettes and film to the farm to allow for "repeats" and unexpected views. This precaution would not apply to digital radiography, but depending on the unit, make sure that all required equipment is included.

Equine Radiography

•Radiographic interpretation and diagnosis •Pre-purchase examinations. Photograph courtesy of Seneca College, Veterinary Technician Program, King City, ON Radiographic Interpretation and Diagnosis •Keep the same principles in mind as when viewing radiographs of small animals: •The medial aspect of the limb and the horse's head should be to the viewer's left. •You should have an understanding of the normal anatomy. •Use a systematic approach making sure to view the whole film. •Mostly to evaluate the bones of the skeleton; thus, any response of the bone to insult or disease is relevant. •Any changes such as sclerosis (causing more of a radiopaque image) or demineralization (radiolucent appearance) may not be visible on the radiograph because a change of at least 30% in the bone mineral matrix is required before radiographic changes are evident.2 •Additional imaging -include ultrasonography as well as cross-sectional imaging modalities such as computerized tomography (CT), magnetic resource imaging (MRI), scintigraphy, and further diagnostic testing. •Modalities such as nuclear scintigraphy and thermography not only show subtle changes to the bone but also demonstrate soft tissue, such as ligaments, tendons, and articular cartilage that are poorly imaged on radiographs. Pre-Purchase Examinations •Pre-purchase examination of a horse often prior to buying a competitive or breeding prospect. •Reduce the buyer's risk and assess the current health and athletic soundness of the horse. •Is not a guarantee of the health or soundness of the horse, but an interpretation of the ability of the horse to meet the intended purpose of the procurer. •Extensive radiographs depending on level of expected performance or value of the • It is critical for all parties to identify any potential conflict of interest that may exist. •The veterinarian requested to perform such an examination must clearly identify his or her relationship with or prior knowledge of the horse and the owners or trainers of the horse to be purchased. •It is recommended to have a legal agreement prepared and signed that clearly identifies any relationship or knowledge to protect the interest of the performing veterinarian.

Remember Your Checklist.

•Settings, image receptor, correct body part, center, and borders correct, collimate •Label placement •Central ray •Parallel •Perpendicular.

Equine Radiographic Positions.

•Views •Positioning devices •Borders •Collimate •Central ray. Radiograph and cassette tunnel photograph, courtesy of Dr. Usha Knabe, Knabe Equine Veterinary Service, Orangeville, ON. Remainder photographs courtesy of Seneca College, Veterinary Technician Program, King City, ON •Because equine skeletal structures are large and complex, multiple views are required. •Refer to Chapter 17 for a review of some of the basic terminology. •In small animals, generally two views perpendicular to each other are taken. •Depending on the condition, horses generally require a minimum of four views for most positions, and six for many joints. •The four common views of most positions are DP, lateral, medial oblique and lateral oblique. •Skyline / flexor view or flexed views may also be required. •Central ray at the area of interest. •Borders of long bones should include the joints proximal and distal •Joints should include ~ 1/3 of the long bones distal and proximal to that joint, depending of the joints involved •If using a cassette tunnel, make sure it is strong enough to support the weight of the horse and is translucent to minimize artifacts on the film. •If using a wooden block, have it high enough so that the beam can be directed in a horizontal plane on the area of interest. Ideally, the block should have a slot to support the cassette close to the limb to minimize distortion. •For the foot, if only the lateromedial view of the digit is needed, then shoe removal, sole cleaning, and foot trimming are not required. •For equal weight-bearing, ideally both front feet should be on a wooden block. If only the affected foot is placed on the block, the distal limb joints are extended. •The opposite limb may need to be lifted to ensure full weight-bearing and to prevent motion. Mention this to the veterinarian if there is not equal weight-bearing. •Keep the image receptor as close and parallel to the limb as possible to minimize object-film distance (OFD) and distortion. •Always ensure that the assistant is not standing behind the image receptor in the beam direction; a cassette holder should be used when possible. •Collimate the beam inside the film edges. •The central ray should always be perpendicular to the axis being radiographed. The suggested angle with the ground may change depending on the limb confirmation of the patient. •Place directional markers on the lateral aspect of the limb. •Table 26-2 lists the views that are used in equine limb examination.