Where is the central ray centered for an AP axial projection of the mandible?

The Towne view is an angled anteroposterior radiograph of the skull and visualizes the petrous part of the pyramids, the dorsum sellae and the posterior clinoid processes, which are visible in the shadow of the foramen magnum.

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Indications

This projection is used to evaluate for medial and lateral displacements of skull fractures, in addition to neoplastic changes and Paget disease.

The axiolateral oblique mandible view allows for visualization of the mandibular body, mandibular ramus, condylar process and mentum.

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Indications

This projection is useful in identifying structural changes and displaced fractures of the mandible in a trauma setting, and in neoplastic or inflammatory changes. Given that this view is performed bilaterally, it allows for comparison of both sides of the mandible too.

Patient position

• the patient is seated upright with the side of interest closest to the detector

• the head is first placed in a true lateral position

  • interpupillary line (IPL) perpendicular and midsagittal plane (MSP) parallel to the detector

• then, the neck is sufficiently extended to prevent superimposing the mandibular rami over the cervical spine

• the vertex (top of the head) is lastly tilted towards the detector to

  • demonstrate the region of the mandible of interest

  • prevent superimposing the opposite side

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Technical factors

• left and right axiolateral oblique

• centering point

  • central ray 25-30º cephalic, beam to exit at mandibular region of interest

• collimation

  • no more than 10 x 10 cm with mandible of interest in the middle of the image

• orientation

  • portrait

• detector size

  • 18 cm x 24 cm

• exposure

  • 70-75 kVp

  • 16-25 mAs

• SID

  • 100 cm

• grid

  • yes

Image technical evaluation

• the ramus of interest is shown with no superimposition of the opposite mandible

• the mandibular ramus is not superimposed over the cervical spine

Practical points

• set up the x-ray tube and detector in advance; due to neck extension and tilt, patients may struggle to remain in the particular position for long, hence reducing image stability

  QuestionAnswer Where is the IR centered for a lateral projection of the facial bones? Lateral surface of the zygomatic bone midway between the outer canthus and the EAM. For a lateral projection of the facial bones, what line is perpendicular to the front edge of the IR? IOML Where is the CR directed for a lateral projection of the facial bones? Lateral surface of the zygomatic bone midway between the outer canthus and the EAM The Parietoacanthial projection of the facial bones is commonly called? Waters Method For the Waters Method, the OML forms an angle of ____________ to the plane of the IR? 37 degrees For the Waters method of the facial bones, what line is perpendicular to the plane of the IR? MML What is centered to the IR for a Waters Method projection of the facial bones? Acanthion The Waters Method of the facial bones clearly demonstrates what? Orbits, Maxillae and the Zygomatic Arches Where will the Petrous Ridges be projected for a Waters Method projection of the facial bones? Immediately below the Maxillary Sinuses For a Modified Waters method of the facial bones the OML will form an angle of ___________ to the plane of the IR. 55 Degrees The Reverse Waters method is called a _________________________ projection. Acanthioparietal projection The Modified Waters Method for the facial bones is a good projection to demonstrate what? Blowout fractures How will the Petrous Ridges appear in a Modified Waters projection of the facial bones? Petrous Ridges projected immediately below the inferior border of the orbits midway through the maxillary sinuses. What line is perpendicular to the plane of the IR for a Reverse Waters projection? MML What is the CR angle for a Reverse Waters projection of the facial bones? 0 degrees or perpendicular For a trauma patient with the head immobilized the Central Ray is parallel to what line for a Reverse Waters projection? Parallel to the MML A lateral projection of the facial bones will clearly demonstrate what? All facial bones in their entirety with the zygomatic bones in the center and all left and right side bones superimposed For a lateral projection of the Nasal bones, what line is parallel to the IR? IOML Which side should be placed against the IR for a lateral projection of the nasal bones? Both sides for comparison What line should be perpendicular to the IR for a lateral projection of the Nasal bones? Interpupillary line The PA Axial projection of the facial bones is also called what method? Caldwell What line is perpendicular with the IR for a Caldwell projection of the facial bones? OML How is the Central Ray directed for a Caldwell method of the facial bones? 15 Degrees Caudad to exit the nasion The central ray is perpendicular to what line for the SMV projection of the Zygomatic Arches? IOML Which projection(s) will demonstrate BOTH Zygomatic Arches? SMV and AP Axial (Modified Townes) For the Tangential projection of the zygomatic arches how is the head positioned? MSP 15 degrees toward the side of interest What line should be parallel to the IR for a Tangential projection of the Zygomatic Arches? IOML For the Tangential projection of the Zygomatic Arches how should the top of the head be positioned? Top of the head tilted 15 degrees AWAY from the side of interest. For the Tangential projection of the zygomatic arches the CR is perpendicular to what line and enters where? Perpendicular to the IOML (and zygomatic arch) entering 1" posterior to the outer canthus For the AP Axial projection of the Zygomatic Arches, what line is perpendicular to the IR? OML For the AP Axial projection of the Zygomatic arches, the CR enters where? Glabella (1" above the nasion) The AP Axial projection of the Zygomatic Arches has a CR angle of what? 30 degrees Caudad What is centered to the IR for a PA projection of the Mandibular Rami? Acanthion Which projections will clearly demonstrate any medial or lateral displacement fractures of the mandibular rami? PA/PA Axial What is the CR angle for a PA Axial projection of the mandibular rami? 20 to 25 degrees Cephalad to exit the acanthion What part of the patient's face will touch the IR for a PA or PA Axial projection of the Mandibular Rami? Nose and Forehead What is the Central Ray angle for an Axiolateral Oblique projection of the Mandible? 25 degrees Cephalad What line is perpendicular to the IR for an AP Axial projection for the TMJ? OML (& MSP) What is the CR angle for an AP Axial projection of the TMJ? 35 Degrees Caudad (Centered between the TMJ's and entering 3" above the nasion) How is the Head positioned to demonstrate the Ramus of the Mandible? True Lateral How is the Head positioned to demonstrate the Body of the Mandible? Rotate the Head 30 Degrees toward the IR How is the Head positioned to demonstrate the Symphysis of the Mandible? Rotate the Head 45 degrees toward the IR What projection will best demonstrate the Condyle and Neck of the Mandible? Axiolateral Oblique projection for the TMJ The MSP of the head is rotated how much for an Axiolateral Oblique projection of the TMJ? 15 Degrees toward the IR What is the Central Ray angle for an Axiolateral Oblique projection of the TMJ? 15 Caudad (entering 1.5" superior to the upside EAM) What should be touching the bucky for a Waters projection? Chin What line should be as parallel as possible to the plane of the IR for the SMV projection of the zygomatic arches? IOML The Central Ray should enter at what level for the SMV projection of the Zygomatic Arches? At a level approximately 1" posterior to the Outer Canthus The Central Ray should enter at what level for the Tangential projection of the Zygomatic Arches? Perpendicular to the IOML and entering at a level approximately 1" posterior to the outer canthus of the side of interest What line is perpendicular to the IR for the PA and PA Axial projection of the Mandibular Rami? OML

  Where is the CR centered for an AP axial projection for the mandible?

  skull/facial bones/sinuses/mandible/.

  What is the central ray direction for the AP axial projection of the TMJs?

  Positioning / Merrills Chapter 20.

  Where is the central ray directed for an AP axial projection of the skull?

  Central Ray: Center at the midsagittal plane 2 1/2 inches (6.5 cm) above the glabella to pass through the foramen magnum at the level of the base of the occiput.

  Where is the CR centered for an AP axial projection of the zygomatic arches?

  Where is the CR centered for an AP axial (Towne's) projection for the zygomatic arches? 1" superior to the glabella to pass through zygomatic arches.