Erin Porter, DVM, DACVR
* Special thanks to Drs. Matt Winter, Dan VanderHart and Kip Berry for many
shared slides and images
Interpretation Principles and
Extrathoracic Structures
Interpretation Principles
Objectives
 Review how to appropriately perform thoracic
radiographs
 X-ray technique
 Understand factors for obtaining high quality radiographs
 Perform proper patient positioning
 Know standard projections and differences between
 Be able to quality control thoracic radiographs
 Develop a systematic approach to thoracic interpretation
Indications
 Respiratory signs

Coughing or dyspnea
 Cardiovascular signs
 Trauma
 Regurgitation
 Weight loss
 Health screen
 Cancer screening/metastatic check
Pitfalls
 Proper Quality Control is the
veterinarian’s responsibility
 Never take a single projection

Numer of views are not the
client’s choice
• Collimate!
Avoid “dog-o-grams”
X-ray technique
 High kVp
 Naturally high contrast region of body
 Maximize latitude (shades of gray)
Radiographic
Technique
kV
95
mA
800
 Highest mA
mSec
3.2
 Shortest time
 Minimizes the effect of respiratory motion
 < 1/60th of a second
mAs
2.5
 Low mAs
 Expose during inspiration
 Collimate to reduce scatter
Projections
 Minimum of TWO orthogonal radiographs
1 - Ventrodorsal (VD) or Dorsoventral (DV)

Names based on entrance to exit of beam
2 - Right or left lateral

Right or left refers to recumbency
 THREE views preferred
 Right and left lateral
 VD or DV
DV or VD?
DV
 DV
 Critical animals
 Better visualization of caudal pulmonary vasculature
 VD
 Easier to get straight
 Better visualization accessory lung lobe and great vessels
VD
Patient Positioning – Lateral
 Pull thoracic limbs forward
 Reduce superimposition by musculature
 Center on heart (Caudal edge of scapula)
 Collimate beam
 Thoracic inlet to caudal lung tips (last rib)
 Thoracic spine to sternum
Positioning – VD or DV
 V- trough is helpful
 Sternum straight
 Lined up with spine
 Collimate
 Thoracic inlet to last rib
Effect of Recumbency
Conspicuity of lung lesions
 Nodule, pulmonary pattern, or mass
Nondependent lobe → up → aerated (gas opaque)
Soft tissue lesions surrounded by air
Dependent lobe → down→ deflated (soft tissue opaque)
Soft tissue lesions less visible due to silhouetting
Effect of Recumbency
Right Lateral
Left Lateral
Diaphragm crura parallel
Right crus cranial to left
CVC inserts into right
Heart is more oval
Diaphragm crura diverge dorsally
Left crus cranial to right
CVC inserts into right
Heart is more round
Effect of Recumbency
VD
Diaphragm crura have 3 humps
Cardiac silhouette is more oval
DV
Diaphragm is one smooth curve
Cardiac silhouette is more round
Effect of Recumbency
Pleural Effusion
Positional Radiography
Humanoid
Sternal Recumbency – Horizontal Beam
Positional Radiography
Evaluation for pneumothorax
Dorsal Recumbency – Horizontal Beam
Lateral recumbency – Horizontal Beam
Positional Radiography
Cranial Mediastinal Evaluation
VD
Patient Erect – Horizontal Beam
Quality Control
 Better films require less
interpretation skills
 Poor films require better
interpretation skills
 Frustrating to interpret
 Difficult to standardize normal
 Improper positioning and
technique lead to interpretation
errors
Quality Control – Exposure
Appropriate mA
 Peripheral areas of analog film should be black
 Rule - Should be able to just outline one’s finger when placed
between film and view boxes
 Digital radiographs should not be grainy (Quantum mottle)
 Indicator of underexposure
Underexposed
Quantum mottle
Quality Control – Exposure
Appropriate kVp
• Check x-ray penetration of organs?
•
•
Dark enough to see dorsal spinous processes through scapula (Lateral)
or vertebrae over heart (VD/DV)
Not so dark that cannot see pulmonary vessels in periphery
Quality Control - Positioning
Is all anatomy included?
 Is the heart centered?
Inspiratory?
Quality Control - Positioning
Is the patient lateral?
 Superimposition of rib heads, costal junctions
Oblique
Lateral
Positioning
Is the patient straight?
 VD or DV



Symmetric
 Ribs similar length
Spine and sternum
superimposed
Dorsal spinous processes
centered on vertebral bodies
 “Tear drop” shape
Examples of improper positioning
Quality Control- Respiration
Inspiration
Expiration
T12
Caudal lung tips extend to T12
Diaphragm further from cardiac silhouette
Larger triangle between cardiac silhouette,
diaphragm and caudal vena cava
Lungs have appropriate opacity
T10
Caudal lung tips cranial to T12
Diaphragm closer to cardiac silhouette
Smaller triangle between cardiac silhouette,
diaphragm, and caudal vena cava
Lungs have increased soft tissue opacity
Principles of Radiographic
Interpretation
Interpretation Paradigm
Must have a systematic approach to
image interpretation!
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

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27
Organ by Organ
Left-to-right
Concentric circles (outside in or inside out)
Compartmental Approach
27
Interpretation Paradigm
Compartmental Approach
 Separate Thorax into 4
Compartments (all views)
 Evaluate Each Compartment
Separately
 Tie It All Together
Create a check list and stick with it!
Compartmental Approach
① Extra-thoracic
② Pleural Space
③ Mediastinum
④ Lungs
Compartmental Approach
① Extra-thoracic
② Pleural Space
③ Mediastinum
④ Lungs
Compartmental Approach
① Extra-thoracic
② Pleural Space
③ Mediastinum
④ Lungs
Compartmental Approach
① Extra-thoracic
② Pleural Space
③ Mediastinum
④ Lungs
Extrathoracic Structures
Extrathoracic Structures
Objectives
 Recognize normal extrathoracic structures
 Review common extrathoracic abnormalities
Extra-thoracic Structures
 Thoracic skeleton
 Vertebrae
 Ribs
 Sternum
 Proximal thoracic limbs
 Muscle, fat, skin
 Intercostal spaces
 Caudal cervical region
 Diaphragm
 Cranial abdominal organs
 Liver
 Stomach
Extrathoracic Structures
Ribs
Trace entire rib margin
 Opacity
 Course/contour
 Alignment
Rt vs Lt – symmetry
Evaluate intercostal spaces
Change your perspective…
Normal Appearances
 Ribs
 Smoothly margined widening
 Stippled mineralization of the costal cartilages
1 yr Bassett Hound
1 yr Dalmatian
Extrathoracic Structures
Common Abnormalities
 Aggressive, traumatic, degenerative skeletal lesions
 Cutaneous/body wall nodules, masses or fake-outs
 Cranial peritoneal abnormalities (fluid, air, masses)
 Cranial abdominal organ abnormalities (liver and
stomach)
 Diaphragmatic hernias
Extrathoracic Structures
Acute Rib Fractures
Chronic Rib Fractures
Extrathoracic Structures
 Sternum
Aggressive lesion
Diskospondylitis
Extrathoracic Structures
Aggressive lesion on scapula
Extrathoracic Structures
Musculoskeletal Abnormalities
Extrathoracic Structures
Nipple fake-out
Nipple-o-gram
Diaphragm Anatomy
 Tendinous center
 Three thin peripheral
muscles
 Par costalis
 Oblique attachment to 8th13th ribs
 Par sternalis
 Attachment to xiphoid
cartilage
 Par lumbalis
 Right and left crura
 Attach at L3-L4
Diaphragm Insertion
L3
L4
L5
Extrathoracic structures
Diaphragmatic Hernia
Extrathoracic structures
 PPDH
Cranial Abdomen
Pneumoperitoneum
Decreased Detail
Cranial Abdomen
Biliary tract calculi
Cranial Abdomen
GDV
Questions?