CT TEACHING LECTURES

CHALLENGE

أوقات شغل غير فائدة من وتحصيله العلم طلب في يكـن لم لولكفى الفراغ

: ت الحنبلي عقيل ابن الوفاء هـ 495أبو

CURRICULUM:Lecture Parts Parts AdditionalLecture1 Anatomy, vascular anatomy 26-32 Radiant Dicom viewerLecture2 Variants, artifacts, trauma,

Hemorrhage, tumors, inflammatory

52-60 PACS

Lecture3 Orbit 33-40 CT technique: image acquisition, WW, WL

Lecture4 PNS-Petrous 41-49, 60-63

MIP, VR, inverted MIP

Lecture5 Neck, thyroid, LN 64-73 word skills

THE ORBITAL CONTENTS

• The orbit contains the globe, the extraocular muscles, the lacrimal gland, the optic nerve and the ophthalmic vessels.

• The whole is embedded in fat • The orbit is limited anteriorly by the orbital

septum = thin layer of fascia that extends from the orbital rim to the superior and inferior tarsal plates, separating the orbital contents from the eyelids

6 Extrinsic ocular muscles: insert into the sclera• 4 recti = superior, inferior,

medial and lateral recti, • origin from a common tendinous ring

= annulus of Zinn : attached to the superior orbital fissure. Insertion = the corresponding aspects of the globe, anterior to its equator.

• 2 obliques = superior, inferior

BLOOD SUPPLY

• The arterial supply of the orbit is from the ophthalmic artery

• The venous drainage of the orbit is through the superior and inferior ophthalmic veins into the cavernous sinus

THE SKULL BASE

The inner aspect of the skull base is made up of the following bones from ant. to post:1. The orbital plates of the frontal bone, with the

cribriform plate of the ethmoid bone and crista galli in the midline

2. The sphenoid bone with its lesser wings anteriorly, the greater wings posteriorly, and body with the elevated sella turcica in the midline;

3. Part of the squamous temporal bone and the petrous temporal bone; and

4. The occipital bone

THE SPHENOID BONE consists of a body and greater and lesser wings.• It houses the sphenoid sinuses -cavernous

sinus and carotid artery run. • A deep fossa superiorly known as the sella

turcica• Anteriorly; tuberculum sellae;

• anterior to it = optic chiasm

• Two bony projections • anterior clinoid processes • The posterior part of the sella = dorsum sellae• posterior clinoid processes

THE TEMPORAL BONE consists of four parts:

1. flat squamous part, which forms part of the vault and part of the skull base

2. pyramidal petrous part, which houses the middle and inner ears and forms part of the skull base

3. aerated mastoid part4. inferior projection known as the

styloid process

COMPUTED TOMOGRAPHY

• CT is an excellent modality for demonstrating the extraocular contents of the orbit The lacrimal gland, extraocular muscles, globe, optic nerve and superior ophthalmic vein are routinely seen The lens has a low water content and is dense on CT

• The bony walls of the orbit are demonstrated, and the foramina of the orbit and related anatomy are readily assessed

• Coronal images are best for assessment of the orbital floor, especially in trauma

MAGNETIC RESONANCE IMAGING 

• MRI demonstrates the soft tissues of the orbit It may be performed in any plane It is of particular value in demonstrating the optic nerve, allowing excellent visualization of the entire nerve, including the intracanalicular segment on vertical oblique images along the nerve’s long axis

• On coronal images the 3rd, 4th and 6th nerves and the first division of the 5th can be seen just below the anterior clinoid process

• Images of the intraorbital part of the optic nerve are performed with fat saturation pulses to help distinguish the optic nerve and its sleeve of dura and cerebrospinal fluid (CSF) from the surrounding high-signal fat

• The lacrimal gland lies lateral to the levator palpebrae

CT IMAGE ACQUISITION

• Acquire = Get & hold

WINDOW VERSUS RECONTRUCTION

WINDOW/LEVEL : WW-WL

Window = how many HU within the 256 shades of gray.• Wider the window (larger #)

• More densities seen• Less contrast

• Narrow window (smaller #)• Less densities seen• More contrast

Level = where is this window centered• More dense tissue higher level• Less dense tissues Lower level

Window Name Window Level Window Width

Lung = Air -400 1500Chest = Mediastinal Window 40 400Abdomen 60 400Brain 40 80Angio 300 600Bone 300 1500

RECONSTRUCTION

• Multiplanar reconstruction• MIP - MinIP – VR• Pixel/ Voxel• Slice/ Slab

MAXIMUM INTENSITY PROJECTION (MIP)

• Maximum Intensity Projection (MIP) consists of projecting the voxel with the highest attenuation value on every view throughout the volume onto a 2D image

MIP

• This method tends to display bone and contrast material–filled structures preferentially, and other lower-attenuation structures are not well visualized.

• The primary clinical application of MIP is :• improve the detection of pulmonary nodules and assess their profusion.

MIP also helps characterize the distribution of small nodules. • In addition, MIP sections of variable thickness are excellent for assessing

the size and location of vessels, including the pulmonary arteries and veins.