28. Principles of interpretation - Thorax

Question 1

What three factors contribute to atelectasis in lateral recumbency?

Answer 1

• weight of e.g. heart
• Reduced excursion of dependent thoracic wall
• Cranial excursion of dependent portion of diaphragm

Question 2

Which cranial lobar vessels are readily identifiied in lateral projections (which projection) and why?

Answer 2

• ONLY RIGHT CRANIAL LOBAR VESSELS PROPERLY VISIBLE-> best visualised in LEFT LATERAL view. In right lateral are dorsally displaced and superimposed on L lateral vessels
• Left cranial vessels usually cannot be seen as superimposed on mediastinum or on other vessels

Question 3

How does the heart differ between lateral projections?

Answer 3

• In LL: Slightly rounded and apex slightly elevated from sternum

Question 4

Why are the caudal lobar vessels better visualised in DV vs VD?

Answer 4

• Magnificaiton
• More parallel to plate
• Less atelectasis

Question 5

How does the cardiac silhouette differ between VD and DV projections?

Answer 5

• IN DV: ventral diaphragm pushed forward, contacting and displacing heart to left
• IN DV: Heart more round

Question 6

Which combination of rx settings is preferred in the thorax and WHY?

Answer 6

• High kVp; low mAs
• Long scale of contrast -> many grey shades. Important as inherent marked contrast provided by lungs