Intro to Equine Diagnostic Imaging

What are the main imaging modalities used in equine?

-Radiograph

-Nuclear Scintigraphy

-Ultrasound

-MRI

-CT

What can radiographs be used to see?

• Image bone

• Image articular and periarticular structures

• Image soft tissues

  • swelling

  • mineralisation

What are the benefits of gantry mounted radiography machines

-Higher output, so radio waves can penetrate deeper tissues

-Rotating anode

What are the limitations of gantry mounted radiography machines?

-More complex, higher risk of malfunction

-Greater possibility for exposure

What are the benefits of portable radiography machines?

• stationary anode (less exposure)

• lightweight

• fewer parts

• longer life

What are the limitations of portable radiography machines?

• limit to kVp + mAs

What does 

• kVp

• mA

• S

mean?

• kVp – speed of electrons (energy of photons)

• mA – number of electrons released

• S - time

What is the exposure factor?

combination of kVp and mA gives overall exposure factor

When determining the optimum film:focal distance for a radiograph machine what should you consider?

By body part

By size of animal

By cassette or film type

By processing type

In equine practice, what would you use radiography to view mainly?

Bone to soft tissue in a static image.

What should be included on a radiograph film report?

• State which area has been imaged

• Critique the quality of film

• Radiographic report

• 1. Recognition phase (Search)

• 2. Descriptive Phase (report)

• 3. Interpretation Phase (Differential diagnoses)

How should you assess film quality of a radiograph?

• positioning

• collimation

• contrast

• exposure

• labeling

• artefacts

What should be done in the recognition phase of a radiographic report?

• Systematic search pattern

• Which structures are visible?- soft tissue, bone, articulations

• Abnormal findings

• Normal findings

• Normal variations

• lesion localisation

What should be done in the descriptive phase of a radiographic report?

Categorise according to radiographic (Rὃntgen) signs:

• Size: Objective measurements or subjectively compared with other normal structures

• Shape

• Position

• Number

• Margination: well defined, poorly defined, sharp or blunt margins etc.

• Opacity : Gas, Fat, Fluid/Soft tissue, Mineral, Metal

What should be done in the interpretation phase of a radiographic report?

• history

• signalment

• clinical signs

• diagnostic tests

In equine practice, what would you use ultrasonography to view?

Soft tissue to bone, can provide both static and dynamic images.

tendons + ligaments > bone

What should be done when preping a patient for an ultrasound?

• clip + clean skin

• ultrasound gel

• darkened area to ease visualisation

What is nuclear scintigraphy used for?

Allows us to measure the turn-over of bone.

In equine practice, what would you use nuclear scintigraphy to view?

Bone to soft tissue but assessing the metabolic activity of these.

How is 99M TC given for nuclear scintigraphy?

intravenous injection

How does nuclear scintigraphy work?

Uses technetium 99 as a marker for calcium (as it is recognised as calcium in the body) and can be detected (as it emits gamma rays) which allows it to quantify how fast calcium is being turned-over.

Technetium 99M selectively binds to remodelling bone and has a half life for approx. 6 hours. A geiger counter can hence measure the depletion of Tc99M which can act as a marker for bone turnover.

Where does increased binding of Tc99M occur?

-Inflammation

-Bone repair/remodelling

-Osteomyelitis

-Neoplasia

Describe how Tc99M travels through different tissues

Phase 1:

-Blood pool

-Immediately (as injected here)

-Stays for up to 2 mins

Phase 2:

-Soft tissue

-Stays for 2-15 mins

-Diffuses into ECF

Phase 3:

-Bone

-Stays for up to 2-3 hours

-Bound to HAP (hydroxyapatite)

Summarise the advantages and disadvantages of nuclear scintigraphy

-Useful addition to the diagnostic work up

-Not to be used as a replacement for nerve blocks or thorough clinical examination.

-Conditions that have primarily soft tissue pathology will not be identified

-Sensitive but not very specific

-Use in combination with other imaging modalities and diagnostic analgesia

In equine practice, what would you use an MRI and CT view?

Soft tissue and bone.

When is MRI imaging generally used in equine medicine?

magnetic resonance imaging

After basic imaging modalities to help advance further diagnoses or obtain a diagnosis.

What are the advantages of MRI?

-High detail

-Non-ionising radiation (lower risk)

-Specific and sensitive so powerful for reaching a diagnosis and giving a prognosis

-Directed treatment

What are the limitations of MRI in equine?

-Slow

-Expensive

-Magnet danger

-Not large enough for horse (usually)

What anatomical location/s are CT scans used for in equine?

-Head

-Some parts of Cervical spine

-Distal limbs

What are the different ways an equine CT can be performed?

• Standing CT – only really practical for heads and some parts of the cervical spine

• GA – distal limbs and head and cervical spine