Positioning and radiographic anatomy of the skull

Positioning and Radiographic Anatomy of the Skull

RADIOGRAPHIC ANATOMY

SkullAs with other body parts, radiography of the skull requires a good understanding of all related anatomy. The anatomy of the skull is very complex, and specific attention to detail is required of the technologist.

The skull, or bony skeleton of the head, rests on the superior end of the vertebral column and is divided into two main sets of bones—the 8 cranial bones and the 14 facial bones. 

CRANIAL BONES (8)The eight bones of the cranium are divided into the calvaria (skullcap) and the floor. Each of these two areas primarily consists of four bones:

Calvaria (Skullcap)

1. Frontal2. Right parietal 3. Left parietal4. Occipital

Floor

5. Right temporal6. Left temporal7. Sphenoid (sfe′-noid)8. Ethmoid (eth′-moid)

POSITIONING CONSIDERATIONS

Erect versus Recumbent

Projections of the skull may be taken with the patient in the recumbent or erect position, depending on the patient's condition. Images can be obtained in the erect position with the use of a standard x-ray table in the vertical position or an upright Bucky. The erect position allows the patient to be quickly and easily positioned and permits the use of a horizontal beam. A horizontal beam is necessary to visualize any existing air-fluid levels within the cranial or sinus cavities

Patient ComfortPatient motion almost always results in an unsatisfactory image. During skull radiography, the patient's head must be placed in precise positions and held motionless long enough for an exposure to be obtained. Always remember that a patient is attached to the skull that is being manipulated. Every effort should be made to make the patient's body as comfortable as possible, and positioning aids such as sponges, sandbags, and pillows should be used if needed.

Except in cases of severe trauma, respiration should be suspended during the exposure to help prevent blurring of the image caused by breathing movements of the thorax. This is especially important when the patient is in a prone position.

HygieneCranial and facial radiography may require the patient's face to be in direct contact with the technologist's hands and the table/upright Bucky surface. Therefore, it is important that proper handwashing techniques and surface disinfectants be used before and after the examination.

Exposure FactorsThe principal exposure factors for radiography of the skull include the following:

•Medium kV (65 to 85 kV film-based) (70 to 80 kV digital radiography [DR] and computed radiography [CR])•Small focal spot <250 mA (if equipment allows)•Short exposure time

SIDThe minimum SID with the image receptor in the table or upright Bucky is 40 inches (100 cm).

Radiation ProtectionThe best techniques for minimizing radiation exposure to the patient in skull radiography are to (1) use good collimation practices, (2) immobilize the head when necessary, minimizing repeats, and (3) center properly.

Gonadal shieldingGenerally, with accurate collimation, no detectable contribution to gonadal exposure occurs during radiography of the skull. However, lead shields should be used to reassure the patient

Digital Imaging ConsiderationsGuidelines for digital imaging (CR and DR) of the skull are:

1.Correct central ray angle and centering to body part and image receptor. This provides for accurate post-processing of the image by the image reader.

2.Close collimation. Improves image quality by reducing scatter and secondary radiation to the highly sensitive digital image receptors.

3.Following ALARA principles (exposure to patient As Low As Reasonably Achievable) in determining exposure factors (highest kV and lowest mAs that will result in desirable image quality). An increase in kV over film-screen imaging may be desirable, both for reducing patient exposure and for improving image quality. (Sufficient mAs is required to produce a high-resolution image.)

4.Post-processing evaluation of exposure indices (for assurance that optimum quality image was achieved with least possible radiation to patient). Examine the amount of kV and mAs used for a particular exposure if the exposure index is above or below the recommended range.

Skull Series

BASIC:

• AP axial (Towne method)

• Lateral

• PA axial 15° (Caldwell method) or PA axial 25° to 30°

• PA 0°

SPECIAL

• Submentovertex (SMV)

• PA axial (Haas method)

AP AXIAL PROJECTION: SKULL SERIESTowne Method

Pathology DemonstratedSkull fractures

Technical Factors• IR size—24 × 30 cm (10 × 12 inches), lengthwise

• Moving or stationary grid• 70 to 80 kV range• Small focal spot

Part Position

• Depress chin, bringing OML perpendicular to IR. For patients unable to flex their neck to this extent, align the IOML perpendicular to the IR. Add radiolucent support under the head if needed.• Align midsagittal plane to CR and to midline of the grid or the table/Bucky surface.• Ensure that no head rotation and/or no tilt exists.• Ensure that vertex of skull is in x-ray field.

CollimationCollimate to outer margins of skull.

RespirationSuspend respiration.

If patient is unable to depress the chin sufficiently to bring the OML perpendicular to the IR even with a small sponge under the head, the infraorbitomeatal line (IOML) can be placed perpendicular instead and the CR angle increased to 37° caudad. This maintains the 30° angle between the OML and the CR and demonstrates the same anatomic relationships. (A 7° difference exists between the OML and the IOML.)

Central Ray

• Angle CR 30° caudad to OML, or 37° caudad to IOML (see Note below).

• Center at the midsagittal plane 2½ inches (6.5 cm) above the glabella to pass through the foramen magnum at the level of the base of the occiput.

• Center IR to projected CR.• Minimum SID is 40 inches (100 cm).

Structures Shown: • Occipital bone, petrous pyramids, and foramen magnum are shown with the dorsum sellae and posterior clinoids visualized in the shadow of the foramen magnum.

LATERAL POSITION—RIGHT AND/OR LEFT LATERAL: SKULL SERIES

Pathology DemonstratedSkull fractures. A common general skull routine includes both right and left laterals.

Part Position

• Place the head in a true lateral position, with the side of interest closest to IR and the patient's body in a semiprone position as needed for comfort. • Align midsagittal plane parallel to IR, ensuring no rotation or tilt.

• Align interpupillary line perpendicular to IR, ensuring no tilt of head (see Note below).

• Adjust neck flexion to align IOML perpendicular to front edge of IR

Central Ray

• Align CR perpendicular to IR.• Center to a point 2 inches (5 cm) superior to EAM .• Center IR to CR.• Minimum SID is 40 inches (100 cm).

Structures Shown: • Superimposed cranial halves with superior detail of the lateral cranium closest to the IR are demonstrated. The entire sella turcica, including anterior and posterior clinoids and dorsum sellae, is also shown. The sella turcica and clivus are demonstrated in profile.

PA AXIAL PROJECTION: SKULL SERIES15° CR (Caldwell Method) or 25° to 30° CR

Pathology DemonstratedSkull fractures (medial and lateral displacement)

Part Position

• Rest patient's nose and forehead against table/Bucky surface.

• Flex neck as needed to align OML perpendicular to IR.

• Align midsagittal plane perpendicular to midline of the grid or table/Bucky surface to prevent head rotation and/or tilt.

• Center IR to CR.

Central Ray• Angle CR 15° caudad and center to exit at nasion.• Alternate with CR 25° to 30° caudad, and center to exit at nasion.• Minimum SID is 40 inches (100 cm).

Alternate 25° to 30°: An alternate projection is a 25° to 30° caudad tube angle that allows better visualization of the superior orbital fissures (black arrows), the foramen rotundum (small white arrows), and the inferior orbital rim region. CR exits at level of nasion.

Structures Shown: • Greater and lesser sphenoid wings, frontal bone, superior orbital fissures, frontal and anterior ethmoid sinuses, superior orbital margins, and crista galli are shown.

PA PROJECTION: SKULL SERIES0° CR

Pathology DemonstratedSkull fractures (medial and lateral displacement)

Part Position

• Rest patient's nose and forehead against table/Bucky surface.

• Flex neck, aligning OML perpendicular to IR.• Align midsagittal plane perpendicular to midline of table/Bucky to prevent head rotation and/or tilt (EAMs same distance from table/Bucky surface).

• Center IR to CR.

Structures Shown: • Frontal bone, crista galli, internal auditory canals, frontal and anterior ethmoid sinuses, petrous ridges, greater and lesser wings of sphenoid.

SUBMENTOVERTEX (SMV) PROJECTION: SKULL SERIES

Warning: Rule out cervical spine fracture or subluxation on trauma patient before attempting this projection.

Part Position

• Raise patient's chin and hyperextend the neck if possible until IOML is parallel to IR.

• Rest patient's head on vertex.

• Align midsagittal plane perpendicular to the midline of the grid or table/Bucky surface, thus avoiding tilt and/or rotation.

Central Ray

• CR is perpendicular to infraorbitomeatal line.

• Center 1½ inch (4 cm) inferior to the mandibular symphysis, or midway between the gonions.

• Center image receptor to CR.

• Minimum SID is 40 inches (100 cm)

Structures Shown: • Foramen ovale and spinosum, mandible, sphenoid and posterior ethmoid sinuses, mastoid processes, petrous ridges, hard palate, foramen magnum, and occipital bone are shown.

PA AXIAL PROJECTION: SKULL SERIESHaas Method

Pathology DemonstratedOccipital bone, petrous pyramids, and foramen magnum, with dorsum sellae and posterior clinoids in its shadow

Part Position

• Rest patient's nose and forehead against the table/Bucky surface.

• Flex neck, bringing OML perpendicular to IR.• Align midsagittal plane to CR and to the midline of the grid or table/Bucky surface.

• Ensure that no rotation or tilt exists (midsagittal plane perpendicular to IR).

Central Ray

• Angle CR 25° cephalad to OML.• Center CR to midsagittal plane to pass through level of EAMs and exit 1½ inches (4 cm) superior to the nasion.• Center image receptor to projected CR.• Minimum SID is 40 inches (100 cm).

Structures Shown: • Occipital bone, petrous pyramids, and foramen magnum are shown, with the dorsum sellae and posterior clinoids visualized in the shadow of the foramen magnum.

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Waters Projection

• Waters projection demonstrates:• Cloudy maxillary

sinuses worse on left.• Sinus infection that

needed antibiotics.

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9.1 P-A Skull

• Measure: A-P at the Glabella

• Protection: Full coat apron with lead to back or half apron draped over back of chair.

• SID: 40” Bucky• No tube angle• Film: 10” x 12” regular

I.D. down (portrait)

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P-A Skull

• Patient seated or standing facing the Bucky.

• Nose and forehead touching the Bucky to get the canthomeatal line perpendicular to film.

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P-A Skull

• Horizontal CR: exit through the glabella.

• Vertical CR: mid-sagittal plane

• Center film to horizontal CR

• Collimation: slightly less than film size.

• Breathing Instructions: Suspended respiration

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P-A Skull

• Make exposure and let patient relax.

• Note: If the patient is done seated, place Bucky tray in the lower Bucky slot. This will allow the patient to get their legs under the Bucky.

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P-A Skull Film

• The entire skull should be on the film.

• There should be no rotation.

• The petrous ridges will be superimposed with the orbits.

• To clear the ridges, the Caldwell view can be taken.

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9.2 Chamberlain-Townes

• The Townes Projection is part of a routine skull series.

• The tube is angled to throw the anterior part of the skull away from the occipital region of the skull.

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Chamberlain-Townes

• Measure: A-P at Glabella• Protection: Half apron or

Coat Apron• SID: 40” Bucky• Tube angle: 35 degrees

Caudal• Film: 10” x 12“ regular

I.D. Down (portrait)

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Chamberlain-Townes

• Patient is seated facing the tube.The chin is tucked into the chest until the canthomeatal line is perpendicular to film. A chair the allows some reclining will make this easier for the patient.

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Chamberlain-Townes

• Horizontal CR: Through the EAM. The Horizontal CR will usually pass through the hair line.

• Vertical CR: mid-sagittal• Film centered to

horizontal CR• Collimation: slightly less

than film size or soft tissue of skull

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Chamberlain-Townes

• Breathing Instructions: Suspended respiration

• Make exposure• Let patient breathe and

relax

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Chamberlain-Townes Film

• The entire skull and especially the occipital region of the skull must be on the film.

• Structure seen include the foramen magnum, petrous ridges, IAC’s and TM Joints

• No rotation of skull

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9.3 Skull Lateral

• Measure: Lateral at EAM• Protection: Full coat

apron or half apron draped over back of chair

• SID: 40” Bucky• Tube angle: none but

may be angled parallel to interpupillary line.

• Film: 12” x 10” I.D. to face (landscape)

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Skull Lateral

• Patient seated of standing facing the Bucky. Rotate the body into an oblique position.

• Turn skull so the affected side is next to the Bucky.

• The interpupillary line must be perpendicular to film and tube.

• Mid sagittal plane parallel to the film.

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Skull Lateral• Horizontal CR:

3/4”superior to EAM• Vertical CR: 3/4”

anterior to EAM or mid skull

• Center film to horizontal CR.

• Collimation: slightly less than film size

• Breathing Instructions: Suspended respiration

• Make exposure and let patient relax.

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Skull Lateral Film

• Entire skull must be on the film.

• There should be no rotation of the skull, orbits and mandible ramus superimposed.

• The facial bones are sinuses will be dark (over exposed).

• Usually both lateral views are taken.

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9.5 Base Posterior Skull

• Routine skull view that can be used to evaluate the upper cervical spine.

• Provides an axial view of C-1 and C-2 as well as the foramen magnum.

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9.5 Base Posterior Skull

• Measure: A-P at Glabella• Protection: Half apron• SID: 40” Bucky• Tube Angle: None but if

patient cannot extend head back far enough to get inferior orbital meatal line perpendicular to horizontal CR tube angle may be needed.

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Base Posterior Skull

• Film Size: 10” x 12” regular I.D. down (Portrait)

• Patient is seated in a reclining chair. The chair is placed about 6” to 10” from Bucky.

• Patient is asked to extend neck back until inferior orbital meatal line is parallel to film with top of skull touching the Bucky.

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Base Posterior Skull

• Horizontal CR: EAM• Vertical CR: mid-

sagittal• Center film to

horizontal CR• Collimation: slightly

less than film size or skin of skull

• Breathing Instructions: suspended respiration

• Make exposure

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Base Posterior Skull

• Assist patient get out of the position. Be very careful that the patient does not hit face on x-ray tube.

• The ability of the patient to lay back in the chair will make the view much easier for all concerned.

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Base Posterior Skull Films

• This basilar view of skull has the patient’s head not extended back far enough. The mandible and frontal skull should be superimposed.

• The I.D. Blocker is on the skull.

• The skull is rotated.

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Base Posterior Skull Films

• If the upper cervical spine or mastoid processes and internal auditory canals are the areas of interest, it is appropriate to cone down to this area.

• Note the ear ring left on the patient.

• There is some rotation.

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Base Posterior Skull Films

• The entire skull is visualized.

• The mandible and frontal region of skull are superimposed.

• With a bright light, the zygomatic arches can usually be seen.

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9.6 Schullers Projection

• The Schullers Projection can be used to evaluate the temporal mandibular joints and mastoid air cells and inner ear.

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9.6 Schullers Protection

• Measure: lateral at EAM• Protection: Lead apron• SID: 40” Bucky• Tube angle: 25 degrees

caudal• Film size: 8” x 10” I.D. up

(portrait)

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Schullers Protection for TMJ

• Patient is seated facing the Bucky. Head is turned to place the affected TMJ next to Bucky.

• Skull should be in a true lateral position. Align the TMJ to the center line of the Bucky.

• The vertical CR should be aligned with TMJ away from film.

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Schullers Protection for TMJ

• If the affected TMJ and the side away from the Bucky is aligned with the Center of the Bucky and Vertical CR, the skull will be in the true lateral position.

• The horizontal CR is aligned with the Affected TMJ (closest to film).

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Schullers Protection for TMJ

• Center film to horizontal CR.

• Collimation: 5” x 5”

• Breathing instructions: Keep mouth closed and don’t breathe move or swallow.

• Make exposure.

• Let patient breathe but remain in the position.

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Schullers Protection for TMJ

• Change cassettes to a new 8” x 10”

• Ask patient to open mouth as far as possible.

• Recheck positioning.

• Breathing Instructions: With mouth wide open, don’t breathe move or swallow.

• Make exposure and let patient relax.

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Schullers Protection for TMJ

• Open and closed mouth view are taken of both TM joints.

• The TMJ closest to the Bucky will be the one seen at the center or top of the film.

• Accurate positioning is essential to being able to compare joints.

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9.7 Caldwell Sinus Projection

• The Caldwell Projection will have the petrous ridges below the orbits.

• Positioning is exactly like the P-A skull with the exception of the use of a 15 degree caudal tube angle to lower the petrous ridges.

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9.7 Caldwell Sinus Projection

• Measure: A-P at Glabella• Protection: Coat apron

backwards or half apron draped over back of chair.

• SID: 40” Bucky• Tube angle: 15 degrees

caudal• Film: 8” x 10” Regular

I.D. Down (portrait)

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Caldwell Sinus Projection

• Patient is seated facing Bucky. Their legs should be under the Bucky. Get chair as close to the Bucky as possible.

• Ask patient to place their nose and forehead on center line of Bucky.

• Check for rotation.

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Caldwell Sinus Projection

• Horizontal CR: exits through the Glabella or Nasion

• Vertical CR: mid-sagittal• Center film to

horizontal CR• Collimation: 6” or 7”

square.• Breathing Instructions:

Suspended Respiration

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Caldwell Sinus Projection Film

• This view will provide a clear view of the frontal and ethmoid sinuses.

• The super orbital rims can be evaluated for fracture when facial bone are of interest.

• To project the petrous ridges farther down, increase angle to 25 degrees

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9.8 Waters Projection Sinus

• The most important view for sinus problems or injury involving the maxilla or orbits.

• By taking the view erect, fluid levels within the maxillary sinuses can be seen.

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9.8 Waters Projection Sinus

• Measure: A-P at Glabella• Protection: Half apron

over back of chair or coat apron backwards

• SID: 40” Bucky• No tube angle• Film: 8” x 10” regular I.D.

Down (portrait)

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Waters Projection Sinus

• Patient is seated facing the Bucky. Get the chair as close to the Bucky as possible. Patient may spread legs to get chair as close as possible. May also be taken standing.

• Mentomeatal line should be perpendicular to film with mouth closed.

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Waters Projection Sinus

• The nose will be one to two centimeters from Bucky with chin resting on Bucky.

• The mouth may be opened to see the sphenoid sinus. When this is done, the canthomeatal line should be 35 to 40 degrees to the Bucky.

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Waters Projection Sinus

• Horizontal CR: exit through the base of nose or acantha.

• Vertical CR: mid-sagittal• Center film to

horizontal CR• Collimation: 6” or 7”

square• Breathing Instructions:

Suspended Respiration

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Waters Projection Sinus Film

• This is an example of the open mouth waters view.

• The facial bones and sinuses should be on the film.

• There should be no rotation.

• The petrous ridges must be below the floor of the maxilla.

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Waters Projection Sinus Film

• The facial bones and sinuses should be on the film.

• There should be no rotation.

• The petrous ridges must be below the floor of the maxilla.

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9.9 Sinus Lateral

• The lateral view of the sinuses and facial bones will under exposed for the skull.

• This view is very useful for seeing fluid levels in all of the sinuses.

•

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9.9 Sinus Lateral

• Measure: Lateral at EAM• Protection: Coat apron

or half apron draped over back of chair.

• SID: 40” Bucky• No Tube Angle• Film: 8” x 10” regular I.D.

down (portrait)

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Sinus Lateral

• Patient is seated or standing facing the Bucky. Turn patient toward the affected side. Turing the body will make it easier for the patient.

• Patient’s skull should be in a true lateral position. The interpupillary line perpendicular to film.

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Sinus Lateral

• Horizontal CR: Outer canthus of the eye with mid sagittal plane parallel to film.

• Vertical CR: Outer canthus of eye

• Center film to horizontal CR.

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Sinus Lateral

• Collimation Top to Bottom: Frontal Sinuses to Mandible

• Collimation Side to side: Nose to EAM

• Breathing Instructions: suspended respiration

• Make exposure and let patient relax

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Sinus Lateral

• There should be no rotation of the patient’s skull.

• The orbits, sella, maxilla and visualized mandible should be superimposed.

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9.10 Basilar View of Sinuses

• The base view of the sinuses is positioned just like the base posterior view.

• The horizontal CR is moved to the center of the facial bones and sinuses.

• The positioning view demonstrates a patient that cannot extend their neck.

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9.10 Basilar View of Sinuses

• Measure: A-P at glabella• Protection: Half or coat

apron• SID: 40” Bucky• Tube angle: none if

patient can extend neck until the inferior orbital-meatal line is parallel to film.

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Basilar View of Sinuses

• If patient cannot extend back far enough, angle tube to get the CR perpendicular to the inferior orbital-meatal line.

• Film: 8” x 10” regular I.D. down (portrait)

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Basilar View of Sinuses

• Position chair about 6” to 10” from Bucky. Patient seated facing the tube.

• Have patient lean back or recline in chair.

• Patient extend neck as far as possible until the inferior orbital-meatal line is parallel to film.

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Basilar View of Sinuses

• Horizontal CR: 1.5” superior to EAM or middle of mandible.

• Vertical CR: mid-sagittal plane

• Center film to horizontal CR.

• Collimation: slightly less than film size or skin of facial region

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Basilar View of Sinuses

• Breathing Instructions: Suspended respiration

• Make exposure• Carefully assist patient

raise head without hitting head on x-ray tube.

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Basilar View of Sinuses

• Mandible and frontal bone should be superimposed.

• No rotation of skull• Maxilla, sphenoid and

ethmoid sinuses and mandible will be seen.