Equine diagnostic imaging

What are the main imaging modalities used in equine?

• Radiography

• Nuclear scintigraphy

• Ultrasonography

• MRI

• Computed tomography (CT)

What is radiography used to image?

• Mainly bone

• Some articular and periarticular structures

• Can see some swelling and mineralisation of soft tissues

(contrast techniques)

What are the differences between portable and gantry machines?

Portable

• Stationary anode —> minimal heat absoprtion

• Limit to kVp and mAs

• Fewer parts = longer life

Gantry mounted

• Rotating anode —> maximum heat absorption

• High kVp and mAs possible

• More complex = more risk of malfunction

• Three phase power supply

What machine settings (exposure factors) can be set on a radiography machine?

kVP = speed of electrons

mA = number of electrons released

S = time

What factors are taken into consideration for optimum film:focal distance?

• By body part

• By size of animal

• By cassette or film type

• By processing type

What are the different image aquisition systems?

• Computed radiography

• Direct radiography

• Conventional

(Everything mainly digital and instant imaging now)

How is film stored as a permanent record?

• As DICOM image —> unique number

• As hard copy

When reporting on images what process should you follow?

• State area that has been imaged

• Critique quality of film

• Make a radiography report

  • 1. Recognition phase (search)

  • 2. Descriptive phase (report)

  • 3. Interpretation phase (Ddx)

What features of film quality should be assessed?

• Positioning

• Collimation

• Contrast

• Exposure

• Labeling

• Artefacts

(Pink Camels Collect Extra Large Apples)

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

• Lesion localisation

• Systematic search pattern

• Identify visible structures

• Normal/abnormal findings

• Normal variations

What should be done in the descrriptive phase of the report?

Categorise according to Rontgen signs

• Size

• Shape

• Position

• Number

• Margination —> well/poorly defined, sharp/blunt margins 

• Opacity

What should be done in the descrriptive phase of the report?

• Take into consideration:

  • History

  • Signalment

  • Clinical signs

  • Diagnostic tests

What are ultrasounds used to view and how do they work?

• Tendons and ligaments

• Sound wave produced by piezoelectric crystal

  • Reflected from tissue interface

  • Degree of reflection determined by tissue density and whether US wave is reflected, absorbed or scattered

What is the advantage of ultrasonography

Safety:

• No ionising radiation!!

• No radiation protection issues!

What are the standard frequencies used in equine ultrasounding?

2.5 - 14 mHz

What are the different configuration of ultrasound probes?

• Linear

• Sector

• Convex/microconvex

What should you choose a probe based off?

• Area dependent —> adequate for depth and resolution

• Type of head and frequency

How is a patient prepared for ultrasound?

• Clip and clean skin

• Ultrasound gel

• Standoff

• Alcohol —> not clipped

What features are used to describe a lesion on an ultrasound?

• Size – actual size or CSA %

• Shape –

• Position

• Number

• Margination - Fibre alignment

• Echogenicity

Assess in transverse and longitudinal images

How does nuclear medicine/gamma scintigraphy work?

Use of radio-isotope —> technetium 90

• Gamma ray emission

• Polyphosphonate binds HAP crystals

• Gamma rays detected

How does the isotope used for nuclear medicine work?

• Binds actively to remodelling bone

• IV injection

• Excreted in urine, half life of 6 hours

What is used to acquire an image in nuclear scintigraphy?

• Gamma camera —> a giant Geiger counter

What are the different types of image acquisition using a gamma camera?

Static —> horse must remain mobile for 60-120 seconds

Dynamic —> same length but corrects for movement by realigning images

What are the phases of scanning in nuclear scintigraphy?

• Phase I – blood pool

  • Rarely used in equine

  • immediate

• Phase II – soft tissue

  • 2-15 minutes

  • Diffusion to extracellular fluid

• Phase III – bone

  • 2-3 hours

  • Bound to HAP

In what cases is nuclear scintigraphy used?

• Mainly bone abnormalities

• Commonly used to diagnose lameness, but can also be used to evaluate other conditions

more intense colour = more gamma rays detected, compare intensity of L vs R, compare regions of interest & ratios

Where is there increase binding of HAP to crystals in nuclear scintigraphy?

• Inflammation

• Bone repair/remodelling

• Osteomyelitis

• Neoplasia

What safety precautions need to be taken in cases of nuclear scintigraphy?

• Isolation of horse for 48 hours

• Minimise contact with radioactive horse

• Wear gloves when handling

• Contain urine and faeces

• Monitor exposure

  • EPD and personal dose meters

  • Radiation badges

What are 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

What is MRI (magnetic resonance imaging) used for?

• Use after basic imaging modalities to help advance diagnoses further or obtain a diagnosis if basic imaging modalities have failed to do so

• Very limited to lower limb and extremities if not under GA

What are the advantages of MRI?

• Increase detail

• Specific and sensitive

• Directed treatment towards lesions

What are the limitations of MRI?

• Takes a very long time

• Lesions can't really be aged

• Sometimes poorly worked up case

What areas can be examined using equine CT?

• Standing CT —> limited to heads and some parts of the cervical spine

• GA —> distal limbs, head and cervical spine