Lecture 3: Equine Diagnostic Imaging

indication for radiographs

• lameness localized to a specific region

• and you suspect a bony abnormality

• often first line imaging in equine practice

what is the name of this view of a front limb?

lateromedial

radiograph positioning

• horse must stand squarely on the limb being radiographed

• convention → plate is always medial and almost always palmar/plantar

R vs L markers for radiographs

• lateral or dorsal → always lateral when that is an option, if not, then dorsal

• label hind vs fore if hock or carpus is not in view

what view is this?

LM → talus/trochlear ridges are perfectly superimposed

is this image diagnostic quality?

yes

what view is this?

lateromedial (LM)

what view is this?

dorsoplantar (DP)

what view is this?

dorsomedial-plantarolateral oblique (DMPLO)

what view is this?

dorsolateral-plantaromedial oblique (DLPMO)

what view is this?

DLPMO

what view is this?

DMPLO → can’t see accessory carpal

what if no radiologic abnormalities, but suspect bone injury?

• wait 10 days → callus formation, resorption at fracture line

• additional imaging

what imaging is not done under GA if suspect fracture?

MRI, CT

ultrasonography principles

• high-frequency sound waves penetrate tissue and bounce back to transducer

• crystals in transducer convert sound waves to electric current

• computer in ultrasound machine converts electric current to image

ultrasonography indications

• image soft tissue lesions → tendons, ligaments, joints

• image surface of bone

ultrasonography of the equine limb

• must clip hair

• remove grease with alcohol

• lots of gel

• 8-15 mHz transducer

• standoff provides better detail in areas with less soft tissue

with increasing mHz of transducer, how does the image change?

decrease depth and increase resolution

well-defined areas for equine distal limb are measured in

zones or distance from accessory carpal bone or point of hock

obvious increase in hypoechogenicity indicates

• core lesion

• fluid = edema = inflammation

increased size of structure in ultrasound

• diffuse lesion

• correlated with increased fluid

what is this?

fiber alignment and echogenicity on longitudinal view

what is this showing?

lesions in 2 different views

indications for nuclear scintigraphy

• fail to localize lameness with blocks

• localize lameness but no lesions on radiographs or ultrasound

• multiple limb lameness

• upper limb or axial musculoskeletal issue

• suspect fracture not imaged on radiographs

principles of nuclear scintigraphy

• inject a drug that is bound to rapidly decaying radioactive atom

• drug has propensity for certain tissue → methylene diphosphonate - hydroxyapatite in bone

• gamma camera detects decay of radioactive atom

• increased bone activity → increased uptake → increased atoms decaying → increased signal

what is the most common radioactive atom used in nuclear scintigraphy?

technetium-99m

hydroxyapatite

• formed by osteoblasts in areas of active bone formation

• proportional to bone resorption

indications for computed tomography

• detailed evaluation of bone → limited soft tissue detail so requires injection of contrast agent

• fracture repair planning

• image navicular apparatus

• image the head

principles of CT

• x-ray tube in circle

• x-rays detected

• intensity of x-ray allows for differentiation of structures

• computer reconstructs the data acquired from detectors to make a slice image

• software programs can reconstruct slices into a 3D image

application of CT

• horse is anesthetized

• imaging limited to → carpus/tarsus and distal limb, head

what is this?

lateral collateral ligament insertional lesion in the navicular bone

MRI indications

• imaging soft tissue and bone lesions → areas where ultrasound is not possible = the foot

• similar limitations in structures that may be imaged as CT

MRI principles

• all tissues have lots of hydrogen protons because they are made of H2O

• magnet is applied and protons are excited by a radiofrequency pulse

• pulse removed → protons relax → emits signal

• protons in different tissues relax differently → superior contrast in tissues

what is this showing?

core lesion in the DDF tendon → desmitis

what is the arrow pointing to?

navicular suspensory ligament

what is this?

adhesion between the navicular bone and the DDFT