Equine Diagnostic Imaging

Question 1

Name 5 diagnostic imaging modalities

Answer 1

• Radiography
• Ultrasonography
• MRI
• Computed tomography
• Nuclear scintigraphy

Question 2

What is kVp?

Answer 2

Speed of electrons (energy of photons)

Question 3

What is mA?

Answer 3

Number of electrons released

Question 4

What is s?

Answer 4

Time

Question 5

What are radiographs?

Answer 5

• Static image of dynamic tissue

- 2-D representation of 3-D object

Question 6

How can you help stop superimposition of structures?

Answer 6

Obtain different views

Question 7

What are the 3 phases of film reading/reporting?

Answer 7

1. Recognition phase (Search)
2. Descriptive Phase (report)
3. Interpretation Phase (Differential diagnoses)

Question 8

Describe the recognition phase

Answer 8

• Systematic search pattern
• Which structures are visible?- soft tissue, bone, articulations
• Abnormal findings
• Normal findings
• Normal variations

Question 9

Describe the descriptive phase

Answer 9

Categorise according to radiographic (Rὃntgen) signs

Question 10

Describe the radiographic (Rὃntgen) signs

Answer 10

• 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

Question 11

Describe the Interpretation Phase (Differential diagnoses)

Answer 11

• History
• Signalment
• Clinical signs
• Diagnostic tests

Question 12

What factors make up film quality?

Answer 12

• Positioning
• Collimation
• Contrast
• Exposure
• Labelling
• Artefacts
  Pink Camels Collect Extra Large Apples

Question 13

Describe the features of ultrasonography

Answer 13

• Non-invasive imaging modality
• Sound wave produced by piezoelectric crystal:
- Reflected from tissue interface
- The ultrasound probe receives the waves back and displays it as a pictorial image on a digital screen
- Degree of reflection determined by tissue density
• No ionising radiation

Question 14

The US wave can either be?

Answer 14

Reflected
Absorbed
Scattered

Question 15

Attenuation is increased with?

Answer 15

Depth

Question 16

How does air appear on ultrasound?

Answer 16

White

Question 17

How can air affect an image?

Answer 17

Air appears white on an ultrasound image and can affect the image seen – ultrasound gel used to stop this

Question 18

How is contact of the ultrasound improved?

Answer 18

• Clip and clean skin
• Ultrasound gel
• Standoff
• Alcohol: not clipped

Question 19

Describe the ultrasound examination technique?

Answer 19

Systematic
- Proximal to distal
- Transverse and Longitudinal
Comparison 
- To opposite “normal” limb/structure
- To “normal” scan of single structure (liver, kidney, heart)

Question 20

How does bone affect ultrasound?

Answer 20

Bone is a reflector of ultrasound waves so cannot see any structures below this

Question 21

How are lesions describes on ultrasound?

Answer 21

• Size: actual size or CSA %
• Shape, Position, Number
• Margination: Fibre alignment
• Echogenicity
• Assess in transverse and longitudinal images

Question 22

What is the function of gamma scintigraphy

Answer 22

Basis of the machine is to try and detect areas of actively turning over bone

Question 23

What are the 3 phases of gamma scintigraphy scanning?

Answer 23

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

Question 24

Increased binding on gamma scintigraphy occurs in areas of…?

Answer 24

• Inflammation
• Bone repair/remodelling
• Osteomyelitis
• Neoplasia

Question 25

Describe the main features of radiation safety

Answer 25

- Minimise contact with radioactive horse - Wear gloves when handling - Contain urine and faeces - Monitor radiation exposure

Question 26

What are the advantages and disadvantages of gamma scintigraphy?

Answer 26

- 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

Question 27

What does MRI stand for?

Answer 27

Magnetic resonance imaging

Question 28

What are the advantages of MRI?

Answer 28

- Detail +++ - Diagnosis: specific and sensitive - Treatment options: directed treatment versus lesions - Prognosis: single vs multiple lesions

Question 29

What are the limitations of MRI?

Answer 29

- Multiple findings: significance of each/primary finding - Aging of lesions? - Prognosis? - What will happen to the lesion with time? - Will the lesion resolve or not?

Question 30

Describe equine CT

Answer 30

* Standing or GA * Standing CT – only really practical for heads and some parts of the cervical spine * GA – distal limbs and head and cervical spine * As with MRI examinations, CT examination of other parts of the body is not really possible