orbit imaging anatomy
TRANSCRIPT
Imaging Recommendations
Radiography
Ultrasound• First line modality for intraocular lesions• Noninvasive, readily available
CT & MR are complementary techniques; both are indicated for evaluation of complex lesions
CT• Excellent evaluation of orbit aided by natural contrast.
between fat, bone, air & soft tissues.• Easily detects calcifications.
MR
• Optimal soft tissue contrast for globe, optic nerve, orbital structures, and intracranial findings.
• Stronger gradients, faster sequences, surface coils, routine use of fat suppression ± gadolinium improve image quality
RadiographyWATERS PROJECTION
CM- canthomeatal line; CR- central ray.(a, frontal sinus; b, medial orbital wall; c, innominate line; d, inferior orbital rim; e, orbital floor; f, maxillary antrum; g, superior orbital fissure; h, zygomatic-frontal suture; i, zygomatic arch)
CALDWELL PROJECTION
a, frontal sinus; b, innominate line; c, inferior orbital rim; d, posterior orbital floor; e, superior orbital fissure; f, greater wing of sphenoid;g, ethmoid sinus; h, medial orbital wall; i, petrous ridge; j, zygomatic-frontal suture
LATERAL PROJECTION
a, orbital roof; b, frontal sinus; c, ethmoid sinus; d, anterior clinoid process; e, sella turcica; f, planum sphenoidale
BASAL PROJECTION (SUBMENTO-VERTEX)
a, zygomatic arch; b, orbit; c, lateral orbital wall; d, posterior wall of maxillary sinus; e, pterygoid plate; f, sphenoid sinus
OPTIC FORAMEN (RHESE POSITION)
a, right optic canal; b, optic strut; c, superior orbital fissure; d, ethmoid sinus; e, planum sphenoidale; f, greater wing of sphenoid
B-scan probe orientations1. Axial scan is obtained by placing the probe face directly over
the center of the cornea. The resulting B-scan image includes the lens and is bisected
by the optic nerve.
B-scan probe orientations2. Longitudinal B-scan require the probe to be placed on the
conjunctiva overlying the sclera and directed through the vitreous bypassing the lens.
It produce a cross-section of the eye along a specific clock hour, displaying the anterior portion of the eye at the top of the screen and the optic nerve at the bottom.
Imaging protocols
CT• Axial + coronal planes; thin-sections (~ 2 mm),Multislice acquisition • Soft tissue algorithm• Contrast for masses or inflammatory disease• Noncontrast only when in conjunction with MR
MR• Axial: Above orbital roof to orbital floor• Coronal: Back of pons through globe• Thin-section (3-4 mm); small FOV (12-16 cm)• T1 pre-contrast (axial + coronal)• STIR or T2 FSE fat-saturation (axial + coronal)• T1C+ with fat-saturation (axial+coronal)
•Sagittal oblique for optic nerves