Chapter 24

Equine and Large Animal Radiography*

Marg Brown RVT, BEd Ad Ed

The essential joy of being with horses is that it brings us in contact with the rare elements of grace, beauty, spirit, and fire.

—Sharon Ralls Lemons, Author and equestrian

Learning Objectives
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(Courtesy EponaTech LLC, Paso Robles, California.)

Technical Note:

To preserve space, the radiographs presented in this chapter do not show collimation. For safety, always collimate so that the beam is limited to within the image receptor edges. In film radiography, you should see a clear border of collimation (frame) on every radiograph. In some jurisdictions, evidence of collimation is required by law.

Imaging large animals requires good planning, good teamwork, lots of patience, and being prepared to expect the unexpected. The common principles of radiography that apply to small animals also apply to large animals, with the major differences being due to patient size and posture, which necessitate special consideration for areas of patient restraint, equipment, preparation, radiation safety, and positioning devices. Safety of personnel and patient is critical.

Compare the large-animal anatomy with human and small-animal anatomy (Fig. 24.1). The technical terms are similar but common terms differ.

imageimageimageimageimageimage
FIG. 24.1 A, Key terms used in radiography. B, Equine skeleton. C and D, Radiographic anatomy of the left lateral forelimb, which is technically referred to as a lateromedial view. E, Radiographic anatomy of the DP or dorsopalmar (dorsoproximal-palmarodistal) of left forelimb. F, Comparison of the palmar views of the (a) horse's limb, (b) human hand, and (c) ruminant's limb. (C and E courtesy Vetel Diagnostics, San Luis Obispo, California, and Seth Wallack, DVM, DACVR, AAVR, Director and CEO of Veterinary Imaging Centre of San Diego.)

Special Considerations

Restraint and Patient Preparation

Large animals in the standing position are minimally restrained, which is a concern for both human and machine safety. Large animals can easily become startled when confronted with unfamiliar objects, so it is important to minimize sudden movements and loud noises. Keep the behavior of the particular patient in mind, and modify your restraint to take advantage of that behavior, being aware that any sights or sounds such as uncoiling electrical cords or moving positioning devices can startle a typically quiet horse.

Ensure there is a solid ground surface that is level, clean, and nonslippery. The area should be quiet, free of obstacles, and large enough for personnel to move around the horse safely. Sedation may calm the patient and curtail startling that can cause movement blur on the image. Depending on the patient, consider various strategies such as raising the opposite limb, using a twitch, offering food, or using stocks. A competent handler is essential if the horse is being difficult or sedation is not an option.

Movement artifacts, poor positioning of the patient or the x-ray beam, and inadequate exposure are the most common reasons that images must be repeated. Among other inconveniences, any repetition means further radiation dose for the restrainer or the patient. 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 directed correctly.

Proper patient preparation is essential to obtain high-quality radiographs and to minimize radiation exposure. The hair coat should be dry, brushed, and cleared of dirt or other debris. If the foot is being radiographed, it is important to prevent overlying shadows superimposed on the field of view. This is especially true of dorsopalmar/dorsoplantar and oblique views. Remove the shoe and trim back any overgrown portions of the foot. Pick and thoroughly clean the sole and clefts, and then pack the sulci adjacent to and in the center of the frog with a substance of similar radiographic opacity, such as Play-Doh, methylcellulose, or softened soap, to eliminate gas shadows due to the grooves of the frog (Fig. 24.2).

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FIG. 24.2 For diagnostic radiographs of the distal foot, the shoe should be removed and the sole cleaned (A), then packed with a radiolucent material (B). (A courtesy Shannon Brownrigg.)

Double-check that you have all proper equipment and supplies with you, including foot blocks, as well as protective equipment and devices for all personnel to be as far from the primary beam as possible. If film cassettes are used and radiographs are being taken off site, make sure to take enough cassettes and film to the facility to allow for “repeats” and unexpected views. For digital radiography make sure that all required equipment such as spare cords, hand switches, or required batteries is on hand.

image Technician Notes

Debris such as shavings, mud, sand, small stones, and manure may cause radiographic artifacts. Sweep the area you are working in to keep the packing clean and minimize artifacts. Visually inspect and clean the legs and hooves well before taking images of the area. Depending on the size of the foot, try brown paper bags, craft paper, sandwich bags, plastic wrap, paper towel, or dry gauze to keep the packing material from picking up particles.

Radiation Safety and Positioning Devices

All of the radiation safety principles applied to small animals equally apply to large animals. When working with large animals, concern for physical safety often supersedes radiation safety. Thus it is essential to constantly keep the three tenets of radiation safety in mind (shielding, distance, and time).

Portable machines can be particularly dangerous with regard to radiation exposure as they can be aimed in any direction and they use longer exposure times than stationary units to produce diagnostic images due to limited machine power. It is critical for all individuals who will be in the path of the beam, near the beam, or holding the portable x-ray unit to have appropriate and proper fitting protective lead attire, thyroid collars, and a monitoring badge (see Chapter 3).

All personal protective equipment (PPE) must undergo a routine maintenance schedule to evaluate weaknesses and breakage (see Chapters 3 and 9). Proper storage of PPE is important; avoid folding gowns and gloves.

The most significant safety action is to increase one's distance from the primary beam through the use of a cassette holder (Fig. 24.3) and the use of a tripod to hold the x-ray unit if space and circumstances allow. Because the construction of x-ray machines does not allow the primary beam to be centered less than about 10 cm (4 inches) from the ground, a positioning block is needed to raise the affected foot (Fig. 24.4) for most views of the foot and pastern.

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FIG. 24.3 A and B, Commercial cassette holders used for equine positioning.
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FIG. 24.4 An example of positioning devices used to hold the cassette. A, Used for the upright pedal route DP positions. B, Redden Navicular x-ray block. C, Ideal for lateral views of the metacarpus. D, Use for the lateral phalanx and sesamoids. The block can be rotated for a DP weight-bearing view so the beam is parallel to the ground. E, EZ Blox-Strap on X-ray blocks. F, Use of a radiolucent cassette tunnel for the digital plate. G, Homemade cassette tunnel for film cassette. H, Redden offset lateral and DP x-ray positioning block. (B and H courtesy NANRIC, www.nanric.com; E courtesy Equine Digit Support System, Inc., www.ezxrayblox.com.)

Always collimate. The primary beam should only include the area of interest so that all margins of the primary beam are visible on the processed film. In digital imaging the algorithm depends on proper collimation. Stand out of direct or bright light to see the collimator guide-light. Because the horizontal beam is standard, always be conscious of where the beam is directed and where individuals are standing; a cassette holder should be used when possible. To help decrease exposure time, use a fast combination of film and screen if using this system.

The source-image distance (SID) is generally less for large animals, with the common SID being 26 to 30 inches (66 cm-76.2 cm), compared with 40 inches (100 cm) in radiography of small animals. Always use the retractable tape measure to determine the proper SID based on the technique chart. Do not guess! Some units have two small laser pointers at precise angles that merge at the correct distance when the collimator light is on. A shorter SID also helps decrease the exposure time. If the SID changes from what is suggested on the technique chart, keep this formula in mind to change the mAs:

Old mAs×(New SID)2(Old SID)2=New mAs

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Review Chapters 5 and 6 if you need to adjust the image technique.

A cassette tunnel is also useful for digit radiographs to protect the image receptor for dorsopalmar/dorsoplantar and oblique views of the foot. A cassette tunnel can be purchased or can be manufactured out of radiolucent wood (avoid use of nails) or hard plastic durable enough to withstand the weight of the horse. 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 (Fig. 24.4F and G). To minimize a slippery surface, cover with duct tape or use a mouse pad or section of yoga mat between the hoof and tunnel.

If using a foot 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 (Fig. 24.4D). If only the lateromedial view of the digit is needed, then shoe removal, sole cleaning, and foot trimming are not essential. For equal weight-bearing, both front feet should be on a foot block. If only the affected foot is placed on the block, improper pressure of the distal limb joints may affect the accuracy of the diagnosis.

The opposite limb may need to be lifted to ensure full weight-bearing and to prevent motion if equal weight-bearing is not required.

Keep the image receptor as close and parallel to the limb as possible to minimize object-film distance (OFD) and distortion. The suggested angle with the ground may change depending on the limb confirmation of the patient. The central ray should always be perpendicular to the limb axis being radiographed.

image Technician Notes

ALWAYS keep the three principles of radiation safety in mind—time, distance, and shielding—when imaging large animals. Also remember to collimate, collimate, collimate.

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.

Ensure there is an adequate power supply, as line voltage may vary, causing inconsistency in the exposures. These units are generally adequate for radiography of the equine distal limbs, skull, and cranial cervical vertebrae. Keep cords well away from feet to prevent tangling or damage from being stepped on. Position the horse so the cords can reach both the left and right sides. 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. Units should never be left in the vehicle overnight during below-freezing temperatures unless a sufficient warm-up time is taken into consideration before the first exposure.

Depending on the type of unit, the kilovoltage (kV) and milliampere (mA) are generally preset, giving power anywhere from 40 to 120 kV and 15 to 100 mA. Time is usually the variable control, providing values of 0.3 to generally 50 milliampere-seconds (mAs). Newer units have variable kV and mAs. The digital displays allow adjustments of 1- to 5- kV increments. Because of the relatively low mA capacity, movement is a concern. Mobile units can be wheeled from room to room in the same premises, but are generally too cumbersome to be easily moved and transported. The kV and mA capacity is higher, allowing for shorter exposure times and less chance of motion artifacts than with the portable units.

Veterinary specialty referral practices commonly use large units permanently mounted on a set of ceiling rails to allow horizontal and vertical movement. These high-capacity units have the greatest output range (between 800 and 1000 mA), capable of obtaining high-quality radiographs of regions such as the thorax, pelvis, and thoracolumbar vertebrae. It may be difficult to obtain parallel views of the feet because the unit may not reach the ground close enough to prevent obliquity. A supplementary portable unit is often used in these situations.

Exposure factors vary for each machine, so contact the generator manufacturer for a technique chart that can be used as a starting point. See Chapters 5 and 8 for suggested equine charts.

Regular maintenance and calibration of all x-ray units are essential to the consistent production of quality radiographs and maintenance of a safe working environment. Inspections should be implemented as per local regulations.

See Chapter 8 for further information on digital equipment.

image Technician Notes

Electrical power may vary in different barn settings. Power may not have the consistency (brownouts) to produce quality radiographs. Have suitable and safety-approved extension cord(s) for exterior use as part of your equipment list. Proper-length cords are best (the shorter the better).

Equine Radiography

Radiographic Interpretation and Diagnosis

You should have an understanding of the normal equine anatomy. Use a systematic approach, making sure to view the whole image. Review the radiography checklist found in Chapter 15.

The purpose of most radiographs taken in equine practice is 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, as a change of at least 30% in the bone mineral matrix is required before radiographic changes are evident.1

Consideration may need to be given to additional imaging for accurate diagnosis and prognosis. This would include ultrasonography as well as cross-sectional imaging modalities such as computerized tomography (CT), magnetic resonance imaging (MRI), scintigraphy, and further diagnostic testing. CT and MRI show the most detail in all structures, indicating actual soft tissue and cartilage within the foot. Modalities such as nuclear scintigraphy and thermography show problem areas to the bone and soft tissue, such as ligaments, tendons, and articular cartilage that are poorly imaged on radiographs (see Fig. 24.64).

Prepurchase Examinations

Equine clients often request a prepurchase examination of a horse before buying a competitive or breeding prospect. This examination is done to reduce the buyer's risk and assess the current health and athletic soundness of the horse. The examination 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. Depending on the level of expected performance or value of the purchase, this examination may include extensive radiographs.

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 to be purchased and its owners or trainers. 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.

image Technician Notes

Unless otherwise indicated, when the limb is described in this chapter, the forelimb terminology is used, but it is understood that the same principles apply to the hind limb.

Labeling and Terminology

For proper diagnosis and legal requirements, correct labeling is mandatory. As with radiography of small animals, permanent identification of the patient and owner (or purchaser for a prepurchase examination) is required. The specific limb being radiographed should also be identified, as well as the actual position. This includes indicating forelimbs and hind limbs, especially distal to the carpus/tarsus.

As in small-animal radiography, the proximal end of the extremity is at the top of the viewer for DP/PD/CrCd/CdCr views. For the lateral or oblique radiographs, the proximal end points up, and the cranial or dorsal aspect of the limb is to your left.

Conventionally, limb markers should be placed dorsally or laterally. Place directional markers (right/left, front/rear) on the lateral aspect of the limb for DP(CrCd) and oblique views and at the dorsal/cranial aspect for lateromedial views. Use Velcro tabs or duct tape to affix to plate. If there is a swelling on the limb, a marker such as a BB pellet taped on the skin might be useful. If using a digital plate, take images in the order of DP, DLPMO, DMPLO, and LM to move the markers only once.

Because equine skeletal structures are large and complex, multiple views are required. In small animals, generally two views perpendicular to each other are taken. Horses generally require a minimum of four views for most positions, and six for many joints.

Refer to Chapter 15 for a review of some of the basic terminology.

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FIG. 24.5 Terminology of the equine proximal limb views. Inner circle: Common terminology and angles. Outer circle: Proper directional terms for the oblique views taken at the level of the metacarpus. P and Pa, palmar; D, dorsal; Pr, proximal; Di, distal; M, medial; L, lateral; O, oblique.

Dorsolateral-Palmaromedial Oblique (DLPMO)

For the dorsolateral-palmaromedial oblique (DLPMO) view (Fig. 24.6B), 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. So that there is no confusion as to what angle should be used, the proper description for this 45-degree DLPMO view is dorsoproximal 45-degree lateral palmarodistomedial oblique (DPr45L-PaDiMO).

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FIG. 24.6 Description of the terminology of the oblique views on a fetlock radiograph. The dotted lines are the direction of the beam and the red lines are the surfaces of the limbs being imaged. A, DMPLO or dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO). Following the rule and taking the middle two and outer two letters, you are looking at the dorsolateral and palmaromedial surfaces of the limb/medial sesamoid. B, DLPMO or dorsoproximal 45-degree lateral–palmarodistomedial oblique (DPr45L-PaDiMO). Following the rule and taking the middle two and outer two letters, you are looking at the dorsomedial and palmarolateral surfaces of the limb/lateral sesamoid. (Courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)

What is actually being highlighted on this DLPMO projection (Fig. 24.6B) is the portion that is not against the film—specifically the lateral sesamoid in Fig. 24.6B. Note that because this is taken at an oblique angle, the image of the medial proximal sesamoid is obstructed by the distal metacarpus (see Technician Notes). Thus an oblique projection allows the portion of the bone farther from the film to be in profile. The radiograph is like a shadow: the way the beam is directed, the body part on the film is superimposed in the oblique, and the opposite edges are highlighted.

The view is correctly described first from where the beam enters on the limb and then where it exits. Using point of entry to point of exit the DLPMO is technically termed a medial oblique because the beam enters off the midline on the lateral aspect and exits on the medial aspect. The medial aspect is against the film. However, because the lateral portion of the bone is in profile in a DLPMO, practicing veterinarians may refer to the position as a lateral oblique.

image Technician Notes

To help remember which views are highlighted in the oblique views, look at the abbreviation for the view and ignore the “O.” Take the middle two letters and then the outer two letters. In the case of DLPMO, the middle two letters are (LP) and the outer two letters are (DM). So you are looking at the dorsomedial and lateropalmar surfaces of the bone (the red lines in Fig. 24.6B). Because of the angle of the beam, the lateral portion, not the medial aspect, is more in profile. The medial portion is hidden.

Dorsomedial-Palmarolateral Oblique (DMPLO)

The same principle applies to the dorsomedial-palmarolateral oblique (DMPLO) (Fig. 24.6A), but this time 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 travels 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. So that there is no confusion as to what angle should be used, the proper description for this 45-degree DMPLO is dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO).

Taking the two middle and two outer letters once the “O” is removed tells us that the dorsolateral and mediopalmar surfaces (red lines on Fig. 24.6A) will be highlighted. The medial proximal sesamoid is in profile.

Remember the view is correctly described first from where the beam enters on the limb and then where it exits. Using point of entry to point of exit, the DMPLO is technically termed a lateral oblique since the beam enters off the midline on the medial aspect and exits on the lateral aspect. The lateral aspect is against the film. However, because the medial portion of the bone is in profile in a DMPLO, practicing veterinarians may refer to the position as a medial oblique.

In practice, you may hear common terms that are used in place of the correct anatomical terms (Table 24.1) or different modes of describing the beam. Anterior posterior (AP), a human term, is still sometimes used in practice; however, the correct nomenclature is dorsopalmar or dorsoplantar (DP). Common terms are listed here for the purpose of further understanding but are not necessarily the proper nomenclature.

TABLE 24.1

Comparative Terminology of the Human and Equine Limbs
ANATOMICAL TERMFURTHER TERM/ABBREVIATIONCOMMON LAY TERMHUMAN EQUIVALENT
Distal phalanx (Pd)Third phalanx (P3)Coffin or pedal boneDistal phalanx (finger tip)
Distal interphalangeal jointCoffin jointDistal interphalangeal joint
Distal sesamoidNavicular bone
Middle phalanx (Pm)Second phalanx (P2)Short pasternMiddle phalanx
Middle interphalangeal jointPastern jointMiddle interphalangeal joint
Proximal phalanx (Pp)First phalanx (P1)Long pasternProximal phalanx
Proximal sesamoid bonesFetlock
Metacarpal interphalangeal jointFetlock jointMetacarpal interphalangeal joint—knuckle
Metacarpus/metatarsusThird metacarpal/metatarsal bone (M3)Cannon boneMetacarpus /Metatarsus
Second metacarpal bone/metatarsal bone (M2)Short splint bone
Fourth metacarpal bone/metatarsal bone (M4)Long splint bone
Carpometacarpal/carpometatarsal jointKnee joint/hock jointWrist joint/ankle joint
Carpus/tarsusKnee/hockWrist/ankle
Brachioantebrachial/femorotibial jointsElbow/stifleElbow/stifleElbow/knee
Shoulder/pelvisShoulder/hipShoulder/pelvis

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Data from Butler JA, Coles CM, Dyson SJ, et al: Clinical Radiology of the Horse, Osney Mead, Oxford, 1993, Blackwell Science Ltd; Morgan JP: Techniques of Veterinary Radiography, Ames, IA, 1993, Iowa State University Press; Thrall DE: Textbook of Veterinary Diagnostic Radiology, St Louis, 2007, Saunders; Weaver M, Barakzai S: Handbook of Equine Radiography, London, 2010, Saunders.

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FIG. 24.7 Comparison of human and equine skeletal structures.

image Technician Notes

To demonstrate that the opposite projections will be in profile, tape two different objects, such as a pen and pencil, to an empty paper towel roll. Label four sides dorsal, palmar, lateral, and medial, and place a piece of paper behind your “limb.” Use your finger as the x-ray beam and try the oblique views. Notice that the opposite protrusion is in profile. Using a flashlight may also help you visualize the projections better. The radiograph is like a shadow with the way the beam is directed—the part on the film is superimposed, but the opposite edges are highlighted.

image Technician Notes

A human middle finger is equivalent to the front foot of the horse, whereas the hind foot is a human's middle toe (Fig. 24.7). Imagine standing on your middle toes all day. It is no wonder the foot is the most frequently imaged for equine lameness issues.

Equine Radiographic Positioning

Table 24.2 lists the views that are used in equine limb examination.

TABLE 24.2

Views of the Equine Limb Examination
STRUCTURES EVALUATED/ COMMENTSVIEWS/COMMENTSaCOMMON TERMINOLOGY
P3

Dorsal 65-degree proximal–palmarodistal oblique (D65Pr-PaDiO); beam angled to ground, high coronary or upright pedal routes.

Dorsoproximal-palmarodistal (DPr-PaDi) with horizontal beam

Dorsopalmar (DP)
Lateromedial (LM) with foot on block (optional).Lateral (L)
Oblique views especially if a P3 fracture is suspected:
(1) DLPMO
(2) DMPLO
Distal interphalangeal jointDorsal 65-degree proximal–palmarodistal oblique (D65Pr-PaDiO) high coronary route with beam angled to groundDorsopalmar (DP)
Lateromedial (LM) with foot on block to include solar margin of P3 and soft tissues of sole on the radiographLateral (L)
Optional viewsOblique views
(1) DLPMO
(2) DMPLO
NavicularLateromedial (LM)Lateral (L)

Dorsoproximal-palmarodistal oblique (DPr-PaDiO):

OR

Dorsopalmar (DP)
Dorsopalmar (DP)
Palmaroproximal-palmarodistal oblique view (PaPr-PaDiO):Flexor or skyline
D65Pr45L-PaDiMODLPMO
D65Pr45M-PaDiLODMPLO
Pastern P1, proximal interphalangeal joint, P2Lateromedial (LM)Lateral (L)
Dorsoproximal-palmarodistal oblique (D30-45Pr-PaDiO)Dorsopalmar (DP)
Dorsal 35-degree proximal, 35-degree lateral–palmarodistomedial oblique (D35Pr-35L-PaDiMO)DLPMO
Dorsal 35-degree proximal, 35-degree medial–palmarodistolateral oblique (D35Pr-35M-PaDiLO)DMPLO
Metacarpophalangeal/metatarsophalangeal joint/proximal sesamoid bones (fetlock)Dorsal 10-degree proximal–palmarodistal oblique (D10Pr-PaDiO)Dorsopalmar (DP)
Lateromedial (LM) extendedLateral (L)
Lateromedial (LM) flexedFlexed lateral (L)
Dorsoproximal 45-degree lateral–palmarodistomedial oblique (DPr45L-PaDiMO)DLPMO
Dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO)DMPLO
Optional viewsPalmaroproximal-palmarodistal oblique view (PaPr-PaDiO)Flexor/skyline/caudal tangential
Dorsoproximal-dorsodistal oblique (DPr-DDiO)Extensor surface/skyline
Metacarpal/metatarsal cannon bone (M3)Dorsoproximal-palmarodistal (DPr-PaDi)Dorsopalmar (DP)
Lateromedial (LM)Lateral (L)
Lateral splint bone (M4)Dorsoproximal 45-degree lateral–palmarodistomedial oblique (DPr45L-PaDiMO)DLPMO
Medial splint bone (M2)Dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO)DMPLO
CarpusDorsoproximal-palmarodistal (DPr-PaDi)Dorsopalmar (DP)
Lateromedial extended (LM)Lateral (L)
Lateromedial flexed (LM)Flexed lateral (L)
Dorsoproximal 45-degree lateral–palmarodistomedial oblique (DPr45L-PaDiMO)DLPMO
Dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO)DMPLO
Optional viewsDorsoproximal-dorsodistal oblique flexed (DPr-DDiO)Skyline
TarsusDorsoproximal-plantarodistal (DPr-PlDi)Dorsoplantar (DP)
Lateromedial (LM) extendedLateral (L)
Lateromedial flexed (LM)Flexed lateral (L)
Dorsoproximal 45-degree lateral–plantarodistomedial oblique (DPr45L-PlDiMO)DLPMO
Dorsoproximal 45-degree medial–plantarodistolateral oblique (DPr45M-PlDiLO)DMPLO
Tuber calcaneusFlexed plantaroproximal-plantarodistal (PlPr-PlDi)Skyline
RadiusCranioproximal-caudodistal (CrPr-CdDi)Craniocaudal (CrCd)
Lateromedial (LM)Lateral (L)
Optional viewsCaudoproximal-craniodistal (CdPr-CrDi)Caudocranial (CdCr)
Cranioproximolateral-caudodistomedial oblique (CrPrL-CdDiMO)CrLCdMO
Cranioproximomedial-caudodistolateral oblique (CrPrM-CdDiLO)CrMCdLO
Elbow jointCranioproximal-caudodistal (CrPr-CdDi)—standingCraniocaudal (CrCd)
Mediolateral standing (ML)Lateral (L)
Optional viewsCranioproximal-craniodistal oblique (CrPr-CrDiO) of olecranonSkyline or flexor
Lateromedial (LM)Lateral (L)
Mediolateral through the thoracic cavityMediolateral (ML)
Cranioproximal-caudodistal (CrPr-CdDi)—recumbentCraniocaudal (CrCd)
Mediolateral (recumbent) (ML)Lateral (L)
Craniomedial-caudolateral obliqueCrMCdLO

Shoulder

Optional views

Mediolateral (ML)Lateral (L)
Cranioproximal 45-degree medial–caudodistolateral oblique (CrPr45M-CaDiLO)CrMCdLO
Cranioproximal 45-degree lateral–caudodistomedial oblique (CrPr45L-CaDiMO)CrLCdMO
StifleLateromedial (LM)Lateral (L)
Caudoproximal-craniodistal (CdPr-CrDi)Caudocranial (CdCr)
Lateral trochlear ridge and medial femoral condyle (stifle)Caudoproximal 60-degree lateral–craniodistomedial oblique (Cd60L-CrMO)CdLCrMO
Optional stifleCranioproximal-caudodistal (CrPr-CdDi)Craniocaudal (CrCd)
Cranioproximal-craniodistal oblique(CrPr-CrDiO)Skyline patella
Lateromedial flexed (LM)Flexed lateral (L)

imageimage

aPalmar is used in this chart and chapter with the understanding that plantar can be substituted when referring to the hind limb.

Data from Weaver M, Barakzai S: Handbook of equine radiography, London, 2010, Saunders Elsevier; Morgan JP: Techniques of veterinary radiography. Ames, IA, 1993, Iowa State University Press; Butler JA, Coles CM, Dyson SJ, et al: Clinical radiology of the horse, Osney Mead, Oxford, 2008, Wiley-Blackwell; Thrall DE: Textbook of veterinary diagnostic radiology, ed 6, St. Louis, 2013, Elsevier.

image Technician Notes

Keep the principles of good radiographic imaging in mind every time. The body part should be close to and parallel to the image receptor, and the central ray is perpendicular to both. Think radiation safety for each exposure.

The Digit (Foot)

The distal phalanx and the navicular bone comprise the digit or foot. Common indications for imaging the equine foot include localized lameness by clinical examination (pain on pressure from foot testers, increased digital pulses, etc.) or by diagnostic analgesia, laminitis, penetrating wounds, or as required for a prepurchase examination.1

Dorsopalmar (DP): Dorsoproximal-Palmarodistal View of the Digit

The three following views can be taken for the dorsoproximal-palmarodistal (DPr-PaDi) views of the foot. The terminology changes slightly depending on the actual positioning. Because the foot or the beam is at an angle to the ground, the high coronary and upright pedal routes are technically termed DPr-PaDiO views. Note that there is no lateral or medial distinction, so do not get confused.

Comments

Lateral: Lateromedial View of the Digit

The lateromedial view of the distal phalanx is used for all of the bones and joints of the foot.

Comments

Oblique Views of the Digit

Oblique views of the distal phalanx and navicular bone are as follows:

Navicular Bone (Distal Sesamoid)

Lateral: Lateromedial View of the Navicular Bone

Positioning, Central Ray, and Collimation

Positioning, central ray, and collimation instructions are the same as those for the lateromedial view of the distal phalanx (Fig. 24.14).

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FIG. 24.14 A, Positioning for the lateromedial view of the navicular bone standing on a block. B, Lateromedial radiograph of the navicular bone. (B courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)

Dorsopalmar (DP): Dorsoproximal-Palmarodistal Oblique Views of the Navicular Bone

High Coronary Stand-on Routes
Dorsal 65-Degree Proximal–Palmarodistal Oblique (D65Pr-PaDiO) of the Navicular Bone

The D65Pr-PaDiO view projects both borders and extremities of the navicular, and the distal border can be seen through the distal and palmar (plantar) portions of the middle phalanx (Fig. 24.15).

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FIG. 24.15 A, Positioning for the dorsoproximal (DP) view of the navicular with the high coronary view angled 45 degrees to the ground (dorsal 45-degree proximal–palmarodistomedial oblique). B, Positioning for the dorsoproximal (DP) view of the navicular with the high coronary view angled 65 degrees to the ground. C, Radiograph of the DP (D60-65Pr-PaDiO)-high coronary navicular position. Note the air artifact along the clefts of the frog due to improper packing of the sole. (A and B courtesy Dr. Usha Knabe, Knabe Equine Veterinary Services, Orangeville, Ontario.)
Upright Pedal Route of the Navicular Bone

Place the foot with the toe tipped so that the dorsal wall is positioned 80 degrees or 90 degrees from the horizontal for the navicular bone (Fig. 24.16).3

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FIG. 24.16 A, An alternate upright pedal route for navicular positioning. The hoof is placed in one of two slots that change the angle at which the central ray strikes the navicular, giving both 80-degree and 90-degree DP views. This block was custom made but commercial 45 and 65 degree navicular blocks can be purchased. B, Positioning for the upright pedal route of the navicular with the foot tipped so that the dorsal wall is positioned 90 degrees from the horizontal to show the proximal border and extremities of the distal sesamoid. The arrow indicates the horizontally directed central ray. C, Radiograph of the DP equine upright pedal route for the navicular with the dorsal wall positioned 80 degrees. (C courtesy Vetel Diagnostics, San Luis Obispo, California; and Seth Wallach, DVM, DACVR, AAVR, Director and CEO of Veterinary Imaging Centre of San Diego.)

Flexor/Caudal Tangential/Skyline (Palmaroproximal-Palmarodistal Oblique) View of the Navicular Bone

The Pastern

Middle and Proximal Phalanx, Proximal Interphalangeal Joint (Pastern)

The main indications for radiography of the middle and proximal phalanx and proximal interphalangeal joint are lameness localized with clinical examination or diagnostic analgesia and penetrating wounds. Specific views of this area are best obtained with the horse bearing weight squarely on all four limbs.

Lateral: Lateromedial View of the Pastern

The lateromedial view of the pastern provides information on the integrity of the foot axis and the bones and joints in the digit.

Dorsopalmar (DP): Dorsoproximal-Palmarodistal Oblique (D30-45Pr-PaDiO) View of the Pastern

The dorsopalmar (D30-45Pr-PaDiO) view of the pastern is a standard view to evaluate the causes of forelimb and hind limb lameness. Additional views of the opposite limb are indicated in patients less than 9 months of age. Comparison studies permit evaluation of physeal closure.2

Oblique Views of the Pastern

Oblique views of the pastern are as follows (Fig. 24.20):

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FIG. 24.20 A, Positioning for the DLPMO view of the right front pastern. B, Radiograph of the DLPMO view of the pastern. C, Positioning of the DLPMO view of the right front pastern. D, Radiograph of the DMPLO view of the pastern. (A and C courtesy Stacey Thompson, BSc, RVT, McKee-Pownall Equine Services; B and D courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)

Metacarpophalangeal/Metatarsophalangeal Joint/Proximal Sesamoid Bones (Fetlock)

Dorsopalmar (DP): Dorsal 10-Degree Proximal–Palmarodistal Oblique (D10Pr-PaDiO) View of the Fetlock

Lateral: Lateromedial (LM) Extended View of the Fetlock

Oblique Views of the Fetlock

Oblique views of the fetlock are as follows:

The DLPMO view is used to view the lateral sesamoid (see Fig. 24.6B and Fig. 24.24A-B), and the DMPLO to view the medial sesamoid (see Fig. 24.6A and Fig. 24.24C-D).

Metacarpus/Metatarsus (Cannon Bone, MII, and MIV)

Dorsopalmar (DP): Dorsoproximal-Palmarodistal (DPr-PaDi) View of the Metacarpus (Mc)/Metatarsus (Mt)

Lateral: Lateromedial (LM) View of the Metacarpus (Mc)/Metatarsus (Mt)

Oblique Views of the Splint Bones

Oblique views of the metacarpus/metatarsus to view the splint bones are as follows:

The DLPMO view is used to evaluate the lateral splint bone (M4), and the DMPLO to evaluate the medial splint bone (M2).

Carpus

The carpus consists of three principal joints with articulation between adjacent bones in each row of carpal bones. This causes overlying images, which may confuse interpretation. Consequently, it is recommended to obtain a minimum of five standard views.3

Dorsopalmar (DP): Dorsoproximal-Palmarodistal (DPr-PaDi) View of the Carpus

Oblique Views of the Carpus

Oblique views of the carpus are as follows:

Skyline: Flexed Dorsoproximal–Dorsodistal Oblique (DPr-DDiO) Views of the Distal Radius, Proximal Row of Carpal Bone, and the Distal Carpal Row1

Radius/Ulna

Craniocaudal (CrCd): Cranioproximal-Caudodistal (CrPr-CdDi) View of the Radius/Ulna

Elbow (Brachioantebrachial Joint)

The elbow joint is difficult to radiograph while the animal is in a standing position because of its proximity to the ventral body wall. The use of general anesthesia is preferred if possible. Because of the increased thickness of the limb, higher-capacity x-ray equipment is required.

Craniocaudal (CrCd): Cranioproximal-Caudodistal (CrPr-CdDi) View of the Elbow

Lateral: Mediolateral (ML) View of the Elbow

With the patient standing, the mediolateral view is the easiest positioning for the elbow and is often suitable for a portable x-ray unit.

Shoulder

To attain quality projections of the shoulder joint, the use of general anesthesia and placement of the patient in lateral recumbency are recommended. The standing position may be possible if the patient tolerates manipulation. The easiest and maybe only view of the shoulder that can be obtained is the mediolateral.

Pelvic Limb Proximal to and Including the Tarsus

Tarsus

Dorsoplantar (DP): Dorsoproximal-Plantarodistal (DPr-PlDi) View of the Tarsus

Oblique Views of the Tarsus

Oblique views of the tarsus are as follows:

Skyline: Flexed Plantaroproximal-Plantarodistal (PlPr-PlDi) View of the Tuber Calcaneus and Sustentaculum Tali

Tibia/Fibula

Caudocranial (CdCr): Caudioproximal-Cranioodistal (CdPr-CrDi) View of the Tibia/Fibula

Stifle (Femorotibial Joint)

Radiography of the femorotibial joint (stifle) is difficult because of the thickness of the surrounding tissue and the sensitive nature of this region. Because of the depth of the muscle in the femoral region, the caudocranial projection demonstrates little above the joint space. Radiographs of this region should be attempted only if the patient is cooperative. Safety is paramount in radiography of the hind region of the horse. Sedation or a twitch may be used; general anesthesia is also to be considered.

Lateral: Lateromedial (LM) View of the Stifle

Caudocranial (CdCr): Caudoproximal-Craniodistal (CdPr-CrDi) View of the Stifle (Optional)

Pelvis and Hip Joints

General anesthesia is required for the pelvic radiographic study of a large animal patient. Young foals (or calves) can be successfully radiographed in the field, whereas larger patients (horses or cows) must be radiographed in the hospital setting because of the specific high-powered radiographic equipment required, such as a mobile or ceiling-mounted unit, to provide proper output (high kV exposure). Views may be segmented to obtain a complete pelvic view (multiple images used for a single view). If using film, the use of a table with an embedded cassette tunnel is preferred to increase ease of positioning and cassette exchange. Due to the thickness of this region, the use of a grid is suggested.

Before administration of a general anesthetic, special consideration must be given to the anesthesia recovery process for patients with pelvic fractures or luxation. As a result, a pelvic radiographic study may be contraindicated.

Ventrodorsal (VD) View of the Pelvis

Head, Neck, Thorax, and Abdomen

Note that for all positions:

See Table 24.3 for further specifics.

TABLE 24.3

Imaging of the Equine Head, Neck, Thorax, and Abdomen
BODY PARTPROJECTIONIMAGE RECEPTOR PLACEMENTX-RAY TUBECENTRAL RAYFURTHER COMMENTS
SkullLateral (Fig. 24.52)Against the affected side.Opposite lateral side.From the opposite side on area of interest.
SkullDorsoventral (DV) (Fig. 24.53)Horizontal ramus against the ventral aspect of the mandible.At the dorsal aspect.Along the midline of dorsal skull on area of interest, perpendicular to the horizontal ramus of mandible.Easier to note asymmetry. Will need increased exposure.
Maxillary sinuses, nasal passageOblique views: Dorso 45-degree lateral–ventrolateral oblique (D45L-VLO) (Fig. 24.54)Ventral, against affected side. Plate is angled 45 degrees.Dorsolateral above the head on the opposite unaffected side.On third and fourth cheek teeth and 45 degrees from parallel plane directed downward.Avoids superimposition of cheek teeth. Best views for maxillary sinuses, frontal sinuses, and both dental arcades. Bilateral recommended.
IncisorD45L-VLOBelow affected jaw and laterally.Above affected jaw and opposite lateral.45-degree angle directed downward on area of interest.
Upper dental arcadeD45L-VLOAgainst affected side laterally.Position laterally against unaffected side on the dorsal head.Downward 45 degrees from horizontal on area of interest.Can reverse so image receptor against unaffected side and beam aimed upward 45 degrees (V45L-DLO).
Lower dental arcadeD45L-VLOUnaffected side ventrally.Laterally to affected side of head dorsally.Downward 45 degrees from horizontal on area of interest.
Frontal regionD30L-VLOAffected side slightly ventrally.Opposite unaffected side slightly above head.30 degrees centered on midline behind eye on the affected side.Avoid inadvertent rostrocaudal angulation. Will need less exposure than if imaging teeth.
TeethV45L-DLO (Fig. 24.55)Above affected jaw (dorsally) and laterally.Below affected jaw (ventrally) and from opposite lateral.45-degree angle directed upward.Alternative view for oblique teeth. For upper dental arcade, the image receptor is placed against the unaffected side.
TeethOcclusal (Fig. 24.56)In the mouth as far caudal as the patient will allow.

Maxillary: dorsal to head

Mandibular: ventral to head.

Maxillary: direct beam downward

Mandibular: direct beam upward at 60-80 degrees from vertical, depending on the conformation of incisors.

Difficult as patient not likely to cooperate without chemical restraint. Need lower exposure than for cheek teeth.
Guttural pouch/larynx/ pharynx/ hyoid bonesLateral (Fig. 24.57)Lateral side of the caudal skull.Horizontal beam opposite lateral side of the skull.Caudal to vertical ramus of mandible (over guttural pouch region). At caudoventral angle of the mandible for the nasopharynx, larynx, and proximal trachea.

Portable unit may be used due to soft tissue density. Position as for routine skull views.

Oblique views can be taken with 10- to 20-degree caudorostral angle.1 Endoscopy is preferred for nasopharynx, larynx, and proximal trachea.

Dorsoventral (DV)Ventral: under the mandible.Dorsal to the head.Midline of the skull over the area of interest.Sedation is highly recommended.
Cervical spineLateral (Fig. 24.58)Side of the cervical region.Opposite side of neck.

Centered on region of choice:

Because of the size of the patient, the cervical spine must be exposed in three views. The patient can be standing or recumbent.
Thoracic spineLateral (Fig. 24.59)Side of the patient on area of interest.Opposite side.Area of interest perpendicular to the image receptor.Often completed for the dorsal spinous processes (withers).
ThoraxLateral (Fig. 24.60)Affected sideHorizontal beam on opposite side.

See comments later for specifics:

Patient standing. Portable unit not powerful enough.
AbdomenLateral (Fig. 24.61)On side (most lesions on midline).Opposite side.

Last rib for small horses:

Multiple laterals required for larger patients.

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FIG. 24.52 A, Positioning for the lateral view of the skull. B, Anatomy of the view of the lateral skull. Radiographs of the lateral skull, cranial aspect (C) and caudal aspect (D). (A courtesy Shannon Brownrigg; C and D courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)
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FIG. 24.53 A, Positioning for the dorsoventral view of the skull. B, Radiograph of the dorsoventral view of the skull. (A courtesy Shannon Brownrigg; B courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)
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FIG. 24.54 Positioning for the oblique view of the skull. (Courtesy Shannon Brownrigg.)
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FIG. 24.55 A, Positioning for the oblique view of the teeth. Also referred to as a lateral 30-degree dorsal-lateroventral oblique. B, Radiograph of the oblique projection of the skull. (A courtesy Shannon Brownrigg; B courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)
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FIG. 24.56 A, The position for an intraoral, rostrocaudal oblique radiograph to evaluate the rostral aspect of the incisive bone and the incisors. The downward arrow is the direction of the central ray for radiography of the maxilla, and the upward arrow indicates the direction of the central ray for the mandibular structures. B, Radiograph of the intraoral rostrocaudal mandibular incisors. Note the fractured incisor.
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FIG. 24.57 A, Positioning for the lateral view of the guttural pouch. Radiographs of the lateral (B). Guttural pouch (C). Larynx/pharynx. (B and C courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)
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FIG. 24.58 A, Positioning of the cervical vertebrae. Note the three areas of centering, C2, C4, and C6. Radiographs of the lateral cervical spine series: B, C1 and C2; C, C3 and C4; D, C4 and C5; E, C6 and C7. (A courtesy Dr. Usha Knabe, Knabe Equine Veterinary Services, Orangeville, Ontario; B to E courtesy Carolyn Bennet, Ontario Veterinary College, Veterinary Teaching Hospital, Diagnostic Imaging at University of Guelph, Ontario.)
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FIG. 24.51 Use of halter or lead shank to prevent artifacts for skull imaging.
Skull Comments

image Technician Notes

The dental formula (see Chapter 22 for further explanation) of the horse is:

*Mares often do not have canine teeth; the first premolars, called wolf teeth, may not be present in either gender.

Other Large-Animal Radiography

Bovine

Even if they are frequently handled, bovine patients have little to no experience of manipulation of their lower extremities, which poses a challenge to perform these radiographs. Maintaining image receptor placement close to the limb without proper restraint devices is almost impossible in most conditions. It is because of these challenges, as well as economic concerns, that radiographs are generally completed only in high-quality or high-producing livestock.

The use of stocks, ropes, and pulley, or ideally, a lift table, will aid in the production of quality radiographs of cattle. The use of stocks provides reduced mobility of the patient; however, they do not limit the mobility of the limbs. Securing the affected limb or, if weight-bearing, rigging an alternate limb through ropes, may be required. The use of a lift table enables the limbs to be secured in a motionless fashion and increases positioning options because the patient can be lifted and tilted off the ground. The lifting of the alternate limb may increase the safety of maneuvering around distal extremities. Sedation or rapid general anesthesia may be used with the bovine patient. The combined use of restraint devices and sedation can significantly increase the safety of personnel, equipment, and the patient for bovine radiographs. Care must be taken to consider the stage of gestation, if applicable, and the potential for recovery trauma.

Equipment requirements and positioning techniques for bovine radiography are the same as those for equine radiography. Handling restrictions may hinder the options and available positions. See Table 24.4 for the common views.

TABLE 24.4

Suggested Views for the Bovine Limb Examination
STRUCTURESCOMMON NAMESPECIFIC TERMINOLOGYaPOSITIONbCENTRAL RAY IS POSITIONED

Digit/foot: P-III (distal phalanx, coffin bone)

P-II (middle phalanx)

P-I (proximal phalanx-pastern) Proximal interphalangeal joint (pastern joint) joint

DP (Standard) (Fig. 24.62B,C)Dorsal 45-degree proximal–palmarodistal (D45Pr-PaDi)Foot slightly forward on image receptor.Perpendicular to foot axis at MSP (midsagittal plane) at area of interest with beam angled ~45 degrees to ground
Lateral (Standard) (Fig. 24.62D)LateromedialOn a block to elevate limb for P-III; resting on ground for other views.90 degrees lateral to MSP, parallel to ground on area of interest: coronary band for PIII
Lateral-interdigit (Optional)Lateromedial (mediolateral) with interdigital filmReceptor between digits. Easiest with patient in lateral recumbency but can be completed standing with foot raised.

90 degrees laterally from MSP to radiograph the lateral claw.

90 degrees medially from MSP medially to radiograph the medial claw.

DLPMO (Optional)

(Fig. 24.62E)

Dorsoproximal 45-degree lateral–palmarodistomedial oblique (DPr45L-PaDiMO)/(DPr45M-PDiLO)As for the lateral view for P-III.45 degrees to ground on the area of interest
DMPLO (Optional)Dorsoproximal 45-degree medial–palmarodistolateral oblique (DPr45M-PaDiLO) (DMPLO)As for the DP view for P-II and P-I

45 degrees lateral to MSP directed either laterally (DLPMO)

or

medially (DMPLO)

Fetlock joint and proximal sesamoid bonesDorsopalmar: DP (Standard)Dorsoproximal-palmarodistal (DPr-PaDi)Foot on ground, full weight-bearing and cassette against palmar aspect.On MSP parallel to the ground, centered at the fetlock
Metacarpophalangeal/metatarsophalangeal articulationLateral (Standard)Lateromedial extended (LM)Foot on ground, full weight-bearing, and cassette against medial aspect.90 degrees laterally from MSP parallel to the ground directed toward the fetlock joint.
DLPMO (Optional)Dorsoproximal 30-degree lateral–palmarodistomedial oblique (DPr30L-PaDiMO) (DLPMO)Foot on ground, full weight-bearing, and cassette against medial aspect of palmar surface45 degrees lateral to MSP directed either laterally (DLPMO).

DMPLO

(Optional)

Dorsoproximal 30-degree medial–palmarodistolateral oblique (DPr30M-PaDiLO) (DMPLO)Foot on ground, full weight-bearing, and cassette against lateral aspect of palmar surfaceOr medially (DMPLO) and parallel to ground on the fetlock joint or the proximal sesamoid bones.
Carpusc

DP

(Standard)

-Dorsoproximal-palmarodistal (DPr-PaDi)Weight-bearing with limbs evenly on ground and cassette on palmar aspect of limb.Parallel to the ground, centered on palpable intercarpal joint space; slightly lateral to MSP since legs are slightly rotated externally when standing.

Lateral

(Standard)

Lateromedial extended (LM)Weight-bearing with limbs evenly on ground and cassette against medial aspect of limb.90 degrees lateral to MSP; parallel to ground just distal and dorsal to prominence of accessory carpal bone.
Elbow jointCdCr (Standard)Caudoproximal-craniodistal- standing (CdPr-CrDi)Weight-bearing with limbs evenly on ground and cassette against cranial aspect of joint at angle to the x-ray beam.Caudal to joint; parallel to ground so beam perpendicular to radius.
Lateral (Standard)Lateromedial standing (LM)Weight-bearing with limbs evenly on ground; cassette against medial aspect of joint at angle to the x-ray beam.90 degrees lateral to MSP, parallel to ground on either the elbow joint or olecranon if required.

CrCd

(Optional)

Cranioproximal-caudodistal standing (CrPr-CdDi)Weight-bearing with limbs evenly on ground and cassette parallel against caudal aspect of olecranon and perpendicular to the lateral chest wall.Directed upward at 20 degrees-30 degrees craniodistal to caudoproximal.
Shoulder

Tangential oblique

(Standard)

Caudomedial-Craniolateral obliquedWeight-bearing with limb in normal position and image receptor placed vertically cranial to shoulder and pushed medially to ensure that the lateral tuberosity of the humerus will be imaged.Caudally and is lateral and slightly dorsal to middle of thorax, angled downward, centered at the craniolateral aspect of the proximal humerus.

Lateral

(Optional since lateral recumbency required)

Mediolateral recumbent (ML)In lateral recumbency with affected limb down and pulled cranially with the humeral head superimposed over the soft tissue of the neck.Above the patient with the beam perpendicular to the ground and centered on the shoulder joint or area of interest.
TarsusDP (two views) (Standard)

Horizontal dorsoplantar (1)

10 degrees dorsoproximal-plantarodistal (2)

For both views:

full weight-bearing with digit pointing slightly outward so beam is not under the patient.

image receptor against plantar aspect of tarsus parallel with calcaneus.

Dorsally and slightly laterally on MSP centered on palpable trochlea.

For view 1: beam is parallel to ground (shows tarsometatarsal joint space)

For view 2: angle 10 degrees downward in dorsoproximal to plantarodistal angle (for intertarsal joint space).

Lateral (Standard)LateromedialWeight-bearing with limbs evenly on ground and cassette against medial aspect of limb.10 cm (4 inches) distal to point of hock.
StifleCaudocranial CdCr (Standard)Caudoproximal-craniodistal standing (CdPr-CrDi)Weight-bearing with limbs evenly on ground and vertical cassette against cranial aspect of patella at right angle to body wall, placed as far proximal and pushed as far medially as abdomen permits.Caudal to the joint and directed downward to obtain a “tunnel” view of the distal femur.
Lateral (Standard)LateromedialWeight-bearing with limbs evenly on ground and cassette against medial aspect of joint.Laterally, parallel to the ground and centered distal and caudal to the patella.
Lateral patella (Optional)Lateromedial (LM) patellaWeight-bearing with limbs evenly on ground and cassette against medial aspect of patella further proximally and cranially than for regular LM view.Parallel to the ground and centered on the patella.

imageimage

aPalmar(o) is used with the understanding that plantar(o) can be substituted when referring to the hind limb.

bFurther specifications with preparation and positioning for the digit: Before a digit radiograph is taken in the bovine patient, the interdigital space and both claws should be cleansed thoroughly and lightly trimmed. If this step is not taken, false images or shadows may mask abnormalities present in the claws. The digits can be viewed radiographically using four angles or projections.6

cOptional views for the carpus include the lateromedial flexed, dorsolateral-palmaromedial oblique (DLPMO), and dorsomedial-palmarolateral oblique (DMPLO). The oblique views are also possible for the elbow joint.

dUsually only the area of the acromion process of the scapula and lateral tubercles of the humerus are visualized on the oblique views and not the character of the shoulder joint. There is extensive scatter radiation due to increased soft tissue. The oblique view is best combined with the lateral view in a recumbent patient.

Further studies of the bovine include pelvis (dorsal recumbency only with hind limbs extended laterally as much as possible); the head (please see the equine for similar positioning); and the spine, thorax, and abdomen (also see as per the equine patient).

Data from Morgan JP: Techniques of Veterinary Radiography, Ames, IA, 1993, Iowa State University Press.

Pelvis, skull, spine, thorax, and abdomen radiographs are completed much like those in horses. In the case of a small calf, radiographs may be performed in the clinic with use of positioning and techniques similar to those used for a large dog. A mobile x-ray machine can be used to take thoracic or abdominal radiographs in a small calf (Fig. 24.62).

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FIG. 24.62 A, Preparation for the imaging of a calf with the use of a horizontal beam. B, Positioning for the dorsopalmar (plantar) radiography of the distal phalanx (PIII). Positioning is similar to that used in equine limb studies. Technically this view would be called a dorsoproximal-palmarodistal oblique (DPr-PaDiO) view. The accurate description is D45Pr-PaDiO because the beam is 45 degrees to the ground. C, Radiograph of cattle DP view of the foot. D, Radiograph of cattle lateral view of phalanx. As per the equine limb, the beam is parallel to the ground and 90 degrees to the MSP (midsagittal plane). E, Oblique view of a cattle foot. (C to E courtesy Carolyn Bennet, OVC. University of Guelph, Ontario.)

Ovine/Caprine/Porcine

Small ruminant patients (sheep/goats) and swine can be radiographed much like small animals (Fig. 24.63). Because they can be easily transported, small ruminant patients are often radiographed within the clinic setting.

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FIG. 24.63 A, Radiograph of lateral view of digits/metacarpus of a swine. B, Radiograph of caprine abdomen. (Courtesy Carolyn Bennet, OVC. University of Guelph, Ontario.)

Because of their minimal handling experience, however, care must be taken to prevent injury due to patient response to fear (i.e., thrashing of limbs). If the patient is horned, special precautions to prevent injury to staff must be taken. Sedation is recommended to produce quality radiographs in an efficient manner.

The fleece of the ovine patient is dense and may contain dirt and debris (i.e., twigs, clumps of mud/stones). Before imaging, carefully inspect for and remove debris that may produce artifacts within the image.

image Technician Notes

Think of positioning cattle for x-rays as being similar to horses with exceptions due to limb angles or anatomy; positioning of sheep and swine is similar to the dog. Restraint is different for all species.

Alternate Modality Images

It is beyond the scope of this text to discuss alternate modalities (Fig. 24.64) in this edition. Additional imaging, such as nuclear scintigraphy, infrared thermal imaging, and MRI, show more features for diagnosis but are considerably more expensive than imaging with the use of x-radiation.

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FIG. 24.64 A, Nuclear scintigraphy of the front limbs indicating dark areas known as “hot spots” or inflammation on the carpus. B, Infrared thermal image of another horse. The red areas indicate “hot spots” or inflammation. (A courtesy Jill McFadden Surette, Toronto Equine Hospital, Mississauga, Ontario; B courtesy Vetel Diagnostics San Luis Obispos, California; and Seth Wallack, DVM, DACVR, AAVR, Director and CEO.)

Fig. 24.65 is a mystery radiograph. Review it and answer the question presented with it.

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FIG. 24.65 Mystery radiograph. What body part and position is this? Where is the image receptor placed?

Review Questions

1. Safety is a priority when taking radiographs. To keep personnel away from the central ray when the metacarpus of large animals is being radiographed, you should:

a. Use a cassette tunnel

b. Use a foot block with a cassette slot

c. Use a cassette holder with a clamp and long handle

d. Hold the cassette

2. When viewing a DMPLO radiograph of the equine fetlock, you should place the image on the viewer so that the proximal cannon bone is positioned:

a. Down with the dorsal aspect to your left

b. Up with the dorsal aspect to your left

c. Up with the dorsal aspect to your right

d. Down with the dorsal aspect to your right

3. To prevent air artifacts when radiographing the equine foot, it is best to use:

a. Play-Doh

b. Sand

c. Styrofoam

d. Plaster

4. The dorsal 65-degree proximal–palmarodistal oblique (D65Pr-PaDiO) view of the distal phalanx means that the beam is angled:

a. To the ground, 65 degrees palmaroproximal

b. 65 degrees from the MSP and to the ground

c. 65 degrees to the limb, dorsoproximal

d. To the ground 65 degrees dorsoproximal

5. The dorsal 65-degree proximal–palmarodistal oblique (D65Pr-PaDiO) view of the digit is also known as a:

a. True DP view

b. Lateral oblique view

c. High coronary view

d. Upright pedal view

6. A human wrist is equivalent to the equine:

a. Proximal phalanx

b. Metacarpal interphalangeal joint

c. Carpus

d. Fetlock joint

7. For the upright pedal route of the navicular bone the foot will be:

a. Pointed on a block with the beam parallel to the ground

b. Placed flat on the tunnel cassette with the beam angled

c. Placed flat on a block with the beam angled to the ground

d. Placed flat on the tunnel cassette with the beam parallel to the ground

8. For a true DP view of the navicular bone, you need to include the:

a. Navicular only

b. P3, navicular, and P2

c. P1, navicular, and P2

d. Coffin bone, navicular, and long pastern

9. The descriptive terminology for a DLPMO is:

a. Dorsal 45-degree proximal lateral–palmarodistomedial oblique

b. Dorsoproximal 45-degree lateral–palmarodistomedial oblique

c. Dorsoproximal 45-degree medial–palmarodistolateral oblique

d. Dorso 45-degree proximal medial–palmarodistolateral oblique

10. You are preparing to image the DMPLO of the digit of a Thoroughbred. The image receptor should be placed at the _______ oblique aspect of the limb and the beam directed dorsal 65-degree proximal and _____________

a. lateral; 45-degree at the lateral

b. lateral; 45-degree at the medial

c. medial; 45-degree at the medial

d. medial; 45-degree at the lateral

11. The veterinarian will request that you complete the DMPLO view of the digit to visualize the __________ wing of the coffin bone, which will appear ____________ on the image.

a. lateral; smaller and denser

b. lateral; larger and less dense

c. medial; smaller and denser

d. medial; larger and less dense

12. To image the fetlock, the image receptor should be placed against the:

a. Medial aspect of the limb, perpendicular to the ground for a flexed lateral view

b. Medial aspect of the limb, perpendicular to the ground for a DP view

c. Medial aspect of the limb, parallel with the ground for a flexed lateral view

d. Lateral side of the limb, perpendicular to the ground for a lateromedial view

13. The splint bones are the:

a. First and fifth metacarpus/metatarsus

b. Second and fourth metacarpus/metatarsus

c. Second and third metacarpus/metatarsus

d. Third and fourth metacarpus/metatarsus

14. You are required to complete a lateromedial view of the metacarpals of an Arabian. The central ray is:

a. On the medial aspect and angled 90 degrees from the MSP

b. Angled to the ground and 90 degrees from the MSP

c. Parallel to the ground and angled 90 degrees from the MSP

d. Parallel to the ground and angled 45 degrees from the MSP

15. To position for the craniocaudal view of the elbow, place the image receptor on the:

a. Palmar aspect of the joint

b. Plantar aspect of the joint

c. Cranial aspect of the joint

d. Caudal aspect of the joint

16. Oblique views are necessary for an equine dental survey to avoid:

a. Increased amount of soft tissue on the head

b. Superimposition of the guttural pouch

c. Superimposition of the frontal sinuses

d. Superimposition of the opposite arcade

17. Pelvic radiographs may be contraindicated in equine patients with a pelvic injury because:

a. Anesthesia poses a risk to the equine patient

b. Patient recovery may cause additional injury

c. Pelvic radiographs are often unsuccessful

d. Pelvic radiographs are never contraindicated

18. The SID for large animals is generally:

a. The same as for small animals

b. Not of concern

c. Shorter than for small animals

d. Longer than for small animals

19. You are required to complete a carpus DP view for a Holstein cow (dairy). You should position the central ray:

a. Parallel to the ground and slightly lateral to the MSP

b. Parallel to the ground on the MSP

c. Parallel to the ground slightly medial to the MSP

d. At a slight angle to the ground on the MSP

20. The view that is completed for cattle but not performed on an equine P3 is the:

a. Lateromedial view

b. Dorsal 45-degree proximal–palmarodistal view

c. Lateromedial (mediolateral) view with interdigital film

d. Dorsal 45-degree lateral–palmaromedial oblique

Chapter Review Question answers are located in the Instructor Resources on Evolve and can be provided to students at the discretion of the Instructor.