Equine Diagnostic Imaging Flashcards by Renee DeAngelis

What is typically the first line of imaging in equine practice? What are 2 indications?

radiographs —> 2 views!

lameness localized to a specific region
boney abnormality suspected

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What is view of the front limb is seen?

a. lateromedial
b. mediolateral
c. dorsopalmar
d. DMPLO

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How is the horse positioned for radiographs? How are they done?

horse must stand squarely on the limb being radiographed

keep the plate medial or palmar/plantar —> some danger to the plate holder

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Where are markers placed on the radiograph plate? When is it especially important to label hindlimb vs forelimb?

lateral or dorsal

if the hock or carpus is not in view —> fetlock

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Which joint is the following radiograph diagnostic for?

a. coffin (DIP)
b. pastern (PIP)
c. fetlock (MCP)

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Label the joints in the following radiograph.

top to bottom

fetlock
pastern
coffin

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Which of the 2 radiographs is considered good quality?

L —> straight joint space

R has staggered condyles and oblique sesamoids, making assessment difficult

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What view is seen in this radiograph?

a. DLPMO
b. DP
c. DMPLO
d. LM

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Is this image diagnostic quality?

yes - straight joint spaces and superimposed bones

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Which image is of diagnostic quality?

R is more oblique - medial talus seen, splint bones are rotated

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Orthogonal views of hindlimb:

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What view is this?

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What view is this?

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What view is this?

DMPLO

highlights DL and PM

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What view is this?

DLPMO

highlights DM and PL

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What view is this?

DLPMO

accessory carpal bone is highlights (lateral) and palmar
L = offset splint bone
DM + PL

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What view is this?

DMPLO

can’t see accessory carpal bone
no L for the splint bone

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What views are these?

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What are 2 options if there is no radiologic abnormalities, but a bone injury is suspected?

wait 10 days for callus formation and resorption at the fracture line
additional imaging - nuclear scintigraphy, MRI, CT (not under GA)

How does ultrasonography work?

high-frequency sound waves penetrate tissue and bounce back to transducer, resulting in denser objects appearing brighter

crystals in transducer convert sound waves to electric current and computer in ultrasound machine converts electrical current into an image

How is echogenicity described?

relative to other objects

anechoic = black, echolucent
hypoechoic = grey
hyperechoic = white

What are the 2 major indications for performing ultrasounds for musculoskeletal disease?

image soft tissues - tendons, ligaments, joints
image bone surface

How is the horse prepared before doing an ultrasound of their limb? What can be used to provide better detail?

clip hair
clean with scrub and alcohol
apply gel to 8-15 mHz transducer (higher, less distance)

Standoff - gel square used in areas with less soft tissue, like tendons

With INCREASING MHz of a transducer, how does the image change?

a. increase depth
b. decrease depth
c. increase resolution
d. decrease resolution

B and C

What approach is used for ultrasounding equine limbs? What should be done if unsure of findings?

block limb into well-defined zones from 1 to 3 (A, B) based on distance (cm) from accessory carpal bone or point of hock

What is seen in this ultrasound on the equine limb?

core lesion of hypoechogenicity, likely fluid, edema, or inflammation

What is occuring in the ultrasound to the right compared to the left?

diffuse hypoechoic lesion increases in size of structure, correlated with increased fluid - typically fully observed with transverse imaging

How is the longitudinal view on ultrasound used to evaluate the equine limb?

transducer runs parallel with muscle fibers ---> evaluates fiber alignment and echogenicity

How are lesions seen on ultrasound properly appreciated?

two views ---> longitudinal (parallel) AND transverse (perpendicular)

What is occurring in these images?

- apical sesamoid fracture - disruption of suspensory ligament two modalities > one

What are 5 indications for performing nuclear scintigtaphy?

1. fail to localize lameness with blocks 2. localize lameness, but no lesions on radiographs or U/S 3. multiple limb lameness 4. upper limb or axial musculoskeletal issue - not easily accessible radiographically and hard to block 5. suspect fracture not found on radiographs used when its hard to walk the horse or radiograph

How does nuclear scintigraphy work?

- inject a drug bound to rapidly decaying technetium-99m - drug (methylene diphosphonate) will have a propensity for hydroxyapatite in bone, which is formed in areas of ACTIVE bone formation, proportional to bone resorption gamma camera is able to detect decay of atom in areas of increased uptake (injuries!)

Nuclear scintigraphy, scapula:

compare to contralateral structure!

What are 4 indications for CT?

1. detailed evaluation of bone (limited soft tissue detail, requires injection of contrast) 2. fracture repair planning 3. image navicular apparatus 4. imaging of the head

How does CT work?

- X-ray tube in a circle rotates and detects intensity of rebounding X-rays - computer reconstructs the data to make a "slice" image and software programs reconstruct slices into 3D images with a continuous view

CT, carpus:

multiple carpal fractures not as easily seen on radiographs

How are horses prepared for CT imaging? What 3 locations is imaging limited to?

anesthetized 1. distal limb 2. carpus/tarsus 3. head - standing!

CT, navicular bone:

lesion at insertion of lateral collateral ligament

What is the main indication for MRI? What limitations exist?

image soft tissue and bone lesions where ultrasound is not possible (foot) same at CT - distal limb, carpus, tarsus, head --> must fit in magnet

How does MRI work?

- hydrogen protons in tissue are excited by magnet in the machine using radiofrequency - as the pulse is removes, the protons relax and emit signals - protons in different tissues relax differently + can use different pulse/relaxation types to create greater contrast and focus on different structures (bone vs. soft tissue)