Skull Positioning

RAD 124

Chapter 20

You might be an x-ray ‘tech’ if: Eating popcorn out of a clean emesis basis is

perfectly natural. You’ve ever had a patient with a nose ring,

tongue ring and 12 earrings say, “I’m afraid of needles!”

You believe a roll of tape can fix any problem! The question of the day is to B.E. or not to B.E.! You have copy x-rays of strange things that you

get out at parties.

Skull Topography:Points, planes & abbreviations Midsagittal plane Interpupillary line Acanthion Outer canthus Infraorbital margin External acoustic meatus (EAM) Orbitomeatal line (OML) Infraorbital line (IOML) Acanthiomeatal line (AML) Glabelloalveolar line (GAL) Glabellomeatal line (GML) Mentomeatal line (MML)

Skull Morphology Mesocephalic: typically shaped head where

petrous ridges project anteriorly & medially at angle of 47 degrees from MSP

Brachycephalic: Short from front to back where petrous ridges lie at 54 degree angle

Dolichocephalic: Long from front to back where petrous ridges lie at 40 degree angle

Technical considerations General body position: Upright or supine

Hyposthenic or asthenic: elevate chest on pillow Hypersthenic: elevate top of head

Cleanliness is important!

Radiation Protection

Use shields whenever possible

Use proper collimation & proper instructions to patient

Review pg. 304-305

Skull Standard views:

Townes Both laterals Waters PA

AP Axial, Towne method: Pg. 316-319 10 x 12, portrait Supine allows easier positioning but

upright OK MSP and OML perpendicular to IR Respiration: suspended CR: 30 degrees caudal entering 2 ½” above

glabella (or 37 degrees to IOML) Exposure index 2150: 80 kVp @ 40 mAs

Lateral, Pg. 306-307 10 x 12, landscape Upright or prone MSP parallel to IR with IOML perpendicular to

front edge of cassette & parallel to long axis of cassette. Interpupillary line perpendicular to IR

Respiration: suspended CR: perpendicular, 2” superior to EAM Exposure index 2200: 15 mAs @ 75 kVp

Parietoacanthial projection Waters method, Pg. 398-399 10 x 12, portrait Upright or supine MSP perpendicular to cassette, chin on IR with

OML at 37 degree angle from plane of cassette Respiration: suspended CR: Perpendicular to IR exiting at acanthion Exposure index 1930: 30 mAs @ 75 kVP

PA, Pg. 310-313 10 x 12, portrait Upright or prone MSP perpendicular to cassette, forehead &

nose on IR with OML perpendicular to cassette

Respiration: suspended CR: perpendicular exiting nasion Exposure index 1910: 20 mAs @ 75 kVp

Trauma Skull Radiography Patient usually supine; routine projections

include:

AP Cross table laterals Acanthioparietal, Reverse Waters AP axial, Towne method

AP, pg. 314-315

OML perpendicular to IR CR perpendicular entering nasion OR parallel

to OML Structures seen are similar to PA, but orbits

considerably magnified

Cross Table Lateral, pg. 308-309

After ruling out spinal injury, elevate head in order to visualize posterior portion

MSP parallel to IR, interpupillary line perpendicular to cassette

CR: perpendicular to IR 2” superior to EAM

Medical Humor A nurse caring for a woman from Kentucky

asked, “So, how’s your breakfast this morning?” “It’s very good, except for the Kentucky jelly. I can’t seem to get used to the taste,” the patient replied. The nurse asked to see the jelly and the woman produced a foil packet labeled ….. …..

“KY Jelly”

Acanthioparietal projectionReverse Waters method

10 x 12, portrait Adjust CR parallel to MML CR enters acanthion

AP Axial, Towne method 10 x 12, portrait If IOML not perpendicular to IR:

Measure from the perpendicular to the IOML and then add 37 degrees

Do not exceed 45 degrees

Non-Trauma Supplemental Skull Radiographs

PA axial, Haas method (pg. 322-323)

Useful for obese, hypersthenic patients OML perpendicular to IR CR 25 degrees cephalic entering 1 ½” below

inion

Submentovertical projectionSchuller method, pg. 324-325

10 x 12, portrait

IOML parallel to IR

CR perpendicular to IOML entering ¾” anterior to EAM

Mastoid Positioning CT has virtually eliminated the need for

mastoid examinations Use proper radiation protection measures,

especially proper beam restriction Always examine mastoids bilaterally Tape the auricles of ear forward Use small focal spot with smallest possible

field size

Standard ProjectionsBilateral Modified Law, Bilateral Stenvers method & Towne method

Axiolateral oblique projection, Modified Law method, Pg. 328-329 8 x 10, portrait Upright or prone with auricle of ear taped forward MSP of head parallel to IR with interpupillary line

perpendicular IOML parallel to IR with head rotated 15 degrees

toward IR Respiration suspended CR angled 15 degrees caudally entering 2” superior and

2” posterior to uppermost EAM

Mastoids – can't. Axiolateral oblique projection, Stenvers

method 8 x 10, portrait Forehead, nose & cheek on IR with IOML

parallel to transverse axis of cassette Head rotated 45 degrees from plane of film

(mesocephalic) CR 12 degrees cephalic entering 3-4” posterior

and ½” inferior to upside EAM

Mastoids – can't. AP axial projection, Towne method

8 x 10, landscape Upright or supine (preferred) OML perpendicular to IR Respiration suspended CR angled 30 degrees caudal to OML entering

2 ½” above nasion

Orbits - Routine Projections: Rhese method & Waters

Parietoorbital oblique projection, Rhese method, pg. 336-337 8 x 10 portrait Upright or prone Center affected orbit to IR with zygoma, nose & chin on

IR with AML perpendicular to plane of cassette Rotate head so that MSP forms 53 degree angle to plane

of cassette Respiration suspended CR: perpendicular entering 1” superior & 1” posterior to

upside TEA (CR exits orbit closest to IR)

Orbit – Con’t. Parietoorbital oblique projection, Rhese

method, pg. 334-335 – can't. Visualizes “on end” view of optic foramen

lying in inferior, lateral quadrant

Lateral deviation indicates incorrect rotation of head

Longitudinal deviation indicates incorrect angulation of AML

Orbits – can't. Parietoacanthial projection, Waters method

Views orbital floor

Eye Organ of vision consists of:

Eyeball Optic nerve (connects eyeball to brain) Blood vessels Accessory organs (extrinsic muscles, lacrimal

apparatus and eyelids

Eye Exposed part of eye is covered by a thin,

mucous membrane known as conjunctiva. Outer, supporting coat of the eyeball in its

posterior segment is called the sclera. Opaque, white sclera called the “white of the

eye” Cornea is in front of the iris (The center

point of the cornea referred to as the pupil.)

Eye Retina: inner coat of the eyeball

Composed of nervous tissue & millions of receptor organs called rods and cones Important radiographically because they play a

role in your ability to see a fluoroscopic image

Eye Projections for eye include a modified

waters method, Pg. 343 OML forms an angle of 50 degrees with the

plane of the IR

See Pg. 343 Generally required prior to MR imaging to

rule out foreign body in the orbits.