Week 10 - ORBITS

A collection of flashcards covering key concepts related to orbit imaging techniques, including positioning, imaging factors, and indications.

What are the three main reasons for orbit imaging?

Pre-MRI screening, trauma, and foreign body localization.

Why is high spatial resolution critical in orbit imaging?

To detect minute metallic foreign bodies.

What factors reduce geometric unsharpness?

Minimal OID, small focal spot, and longer SID.

What is the key difference between PA Axial 30° and standard Caldwell?

The CR is angled 30° instead of 15°.

What are the two options for OML alignment in PA Axial projection?

(1) OML to IR with 30° caudad CR, or (2) Raise OML 30° with perpendicular CR.

What structure should be below the orbital rims in correct PA Axial?

Petrous ridges.

What is the CR direction and point for PA Axial?

30° caudad through mid-orbits.

What is the ideal OML-IR angle for Modified Waters?

50–55°.

Why is Modified Waters better than standard Waters for orbits?

Provides undistorted view of orbital floor.

What is the CR for Modified Waters?

Perpendicular through mid-orbits.

What do the petrous ridges lie within in a proper Modified Waters?

Mid-maxillary sinuses.

How can orbital rotation be assessed?

Compare outer and inner orbital margins; no asymmetry.

What indicates correct Modified Waters positioning?

Petrous ridges midway in maxillary sinuses, no tilt.

Where is CR centered for lateral orbit view?

Outer canthus.

Which lines must be perpendicular/parallel in lateral orbits?

IPL to IR, MSP parallel, IOML parallel.

What structures are shown on lateral orbits?

Entire orbital rims, supra- and infra-orbital margins.

What patient instruction prevents motion during orbit imaging?

Keep eyes fixed on a point or close them still.

What determines whether FB is in the eyeball or orbit?

Comparison of eyes-up and eyes-down projections.

What is the most common projection for Pre-MRI screening?

PA Axial (30° Caldwell).

What should you always remember to include on orbit images?

Correct side markers.