Lecture 3: Equine Diagnostic Imaging

When are equine radiographs indicated?

• Lameness localized to a specific region

• AND you suspect a boney abnormality

• Often first line imaging in equine practice

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

lateromedial

What are the rules for imaging the equine limb?

• horse must stand squarely on limb being imaged

• plate is always medial and almost always palmar/plantar

• R vs L markers are always lateral or dorsal (always lateral first)

Which joint is it diagnostic for?

coffin (DIP)

What view is this?

DMPLO

Is this image diagnostic quality?

yes: the entire carpus is included, the image is sharp, exposure is good, and joint spaces are able to be adequately viewed

What view is this?

lateromedial

What view is this?

dorsoplantar

What is this view and what does it highlight?

DMPLO → highlights DL and PM

What is this view and what does it highlight?

DLPMO → highlights DM and PL

What view is this? And, what structure is lateral on a carpus - is it palmar or dorsal?

DLPMO

accessory carpal bone - palmar and lateral

What is done if a bone injury is suspected, but there are no radiologic abnormalities?

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

• additional imaging: MRI, CT, nuclear scintigraphy

What are the indications for ultrasonography?

• image soft tissue lesions: tendons, ligaments, joints

• image surface of bone

How is ultrasonography of the equine limb performed?

• must clip hair

• remove grease with alcohol

• lots of gel

• standoff provides better detail in areas with less soft tissue (ex. tendons)

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

decrease depth, increase resolution

What could this obvious increase in hypoechogenecity mean?

• core lesion

• fluid = edema = inflammation

The image on the right shows an increased size of a structure. What could this indicate?

• diffuse lesion

• correlated with increase fluid

What 2 views do you need to see a lesion in when ultrasounding an equine limb?

transverse and longitudinal

What are the indications of 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

  • Not easily accessible radiographically

  • Hard to block

• Suspect fracture not imaged on radiographs

What are the principles of nuclear scintigraphy?

• inject drug that is bound to a rapidly decaying radioactive atom (99m Tc)

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

• hydroxyapatite is formed by osteoblasts in areas of active bone formation (proportional to bone resorption)

• gamma camera detects decay of radioactive atom

• increase bone activity → inc uptake → inc atoms decaying → inc signal

What are the indications for equine CT?

• Detailed evaluation of bone

  • Limited soft tissue detail

    • Requires injection of contrast agent

• Fracture repair planning

• Image navicular apparatus

• Image the head

What are the principles of equine CT?

• X-ray tube in circle - rotates at predetermined speed

• X-rays detected

• Intensity of x-ray allows for differentiation of structures (like a radiograph)

• Computer reconstructs the data acquired from detectors to make a “slice” image

• Software programs can reconstruct slices into a 3D image

What locations is equine CT imaging generally limited to?

• carpus/tarsus and distal limb

• head

What is being shown by the arrow on this CT?

lateral collateral ligament insertional lesion in the navicular bone

What are the indications for equine MRI?

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

• similar limitations in structures that may be imaged as CT (horse has to fit in magnet)

What are the principles of equine MRI?

• 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

Are these two arrows pointing at the same thing?

no: white arrow is pointing at a core lesion in the DDF tendon (desmitis) and the yellow arrow is pointing at the navicular suspensory ligament

What is being shown here?

adhesion between the navicular bone and the DDFT