Radiographic Procedures · ARRT 2025
Skull, Face, and TMJ Positioning
The workhorse skull projections (Caldwell, Towne, Waters, SMV, Schueller, Law), cranial baselines, and facial bone routines for the ARRT Radiography Boards.
Overview
Skull, Face, and TMJ is the most projection-heavy chapter on the ARRT registry. The chapter rewards rote memorization of central-ray angulation and the cranial baseline that drives each projection. Three baselines you must know cold: the OML (orbitomeatal line, outer canthus to EAM), the IOML (infraorbitomeatal line, infraorbital margin to EAM, 7° below OML), and the GAL (glabellomeatal line, 7° above OML).
The skull workhorses, by name and angulation: Caldwell PA (CR 15° caudad to OML, demonstrates frontal bone, anterior ethmoid air cells, superior orbital fissures). Towne AP axial (CR 30° caudad to OML or 37° to IOML, demonstrates occipital bone and dorsum sellae projected within foramen magnum). Waters parietoacanthial (CR perpendicular, OML 37° to the IR, demonstrates maxillary sinuses and orbital floors free of petrous ridge superimposition). SMV, submentovertical (IOML parallel to IR, CR perpendicular to IOML, demonstrates skull base, sphenoid sinuses, mandibular condyles).
Facial bones: parietoacanthial Waters and modified Waters for the orbits and maxilla. Lateral face for the nasal bones, sinuses, and mandible body. Mandible series: AP axial Towne for the mandibular condyles, axiolateral oblique for the body and ramus, PA for symphysis. TMJ studies: Schueller axiolateral (CR 25–30° caudad) and Law (CR 15° caudad) for closed and open mouth comparison. Petrous bone routines: Stenvers (PA with 45° head rotation) and Arcelin (AP with 45° rotation).
What you’ll learn in this chapter
The 12 lessons in this chapter break down as follows. The full lesson content is unlocked when you start a free account.
Cranial Anatomy & Baselines
- Cranial Anatomy & Terminology
- Radiographic Baselines
Core Cranial Projections
- PA Axial (Caldwell) & AP Axial (Towne)
- Lateral & SMV (Basal) Projections
Facial Bones
- Waters vs Caldwell for Facial Bones
- Isolating the Zygomatic Arches
Mandible & TMJ
- Mandible: Body and Rami
- Temporomandibular Joints (TMJ)
Knowledge Check
- Question 1 of 4 Quiz
- Question 2 of 4 Quiz
- Question 3 of 4 Quiz
- Question 4 of 4 Quiz
Key terms in this chapter
These are the 7 terms most likely to appear on the ARRT registry from this chapter. Use them as a flashcard pre-quiz.
- OML (Orbitomeatal Line)
- Cranial baseline from the outer canthus of the eye to the external acoustic meatus. Reference for most skull positioning.
- Caldwell Method
- PA skull with CR 15° caudad to OML. Demonstrates frontal bone and anterior ethmoid air cells.
- Towne Method
- AP axial skull with CR 30° caudad to OML. Demonstrates occipital bone and dorsum sellae within foramen magnum.
- Waters Method
- Parietoacanthial projection. OML 37° to IR, CR perpendicular. Demonstrates maxillary sinuses.
- SMV (Submentovertical)
- Skull base projection. IOML parallel to IR, CR perpendicular. Demonstrates sphenoid sinuses and skull base.
- Schueller Method
- Axiolateral TMJ projection with CR 25–30° caudad. Used for closed and open mouth comparison.
- Stenvers Method
- PA petrous bone projection with 45° head rotation. Demonstrates the petrous portion in profile.
Sample practice question: Head, Spine, and Pelvis
One free sample from the 68-question Head, Spine, and Pelvis bank. See the format, the rationale style, and the difficulty before you sign up.
A 45° posterior oblique projection of the lumbar spine demonstrates the Scotty Dog pattern. A defect appearing as a 'collar' on the dog's neck represents which of the following pathologies?
Show answer and rationale
A, Incorrect: Spondylolisthesis is forward slippage of one vertebra on another, best assessed on lateral imaging.
B, Correct: Correct. The Scotty Dog's neck represents the pars interarticularis. A 'collar' on the neck indicates spondylolysis, a defect or fracture of the pars. This finding is pathognomonic on the 45° lumbar oblique.
C, Incorrect: Disk herniation is not directly visible on plain radiographs and requires MRI for diagnosis.
D, Incorrect: Compression fractures involve loss of vertebral body height and are best demonstrated on lateral views.
Hands-on
Practice the positioning
Open the Positioning Lab to drill body position, central ray, anatomy, and common errors for each projection in this chapter.
- Skull Lateral True lateral cranium. SID 40". CR perpendicular to IR.
- Skull AP axial (Towne) AP axial / Towne. Occipital bone, dorsum sellae. SID 40", CR 30° caudad.
- Skull PA axial (Caldwell) PA axial / Caldwell. Frontal bone, frontal & ethmoid sinuses. CR 15° caudad to OML.
- Skull Waters (parietoacanthial) Waters method. Maxillary sinuses, facial bones. MML perpendicular to IR.
- Skull AP AP cranium. SID 40". CR perpendicular to IR.
- Skull PA Forehead and nose on IR. OML perpendicular. CR exits nasion.
- Skull SMV (Cranial Base) Vertex on IR. IOML parallel to IR. CR perpendicular to IOML.
- Facial Bones Parietoacanthial (Waters) Waters method. Maxillary sinuses, facial bones. MML perpendicular to IR.
- Facial Bones Lateral True lateral facial skeleton. SID 40". CR perpendicular to IR.
- Facial Bones PA Axial (Caldwell) Caldwell method. Frontal sinuses, ethmoid, facial bones. CR 15° caudad.
- Nasal Bones Lateral True lateral nasal bones. SID 40". CR perpendicular to IR.
- Mandible PA (Rami) PA mandible. Body and rami. CR perpendicular to IR.
- Mandible PA Axial (Rami) PA Axial mandible. Rami and body. CR 20-25° cephalad.
- Mandible Axiolateral and Oblique Axiolateral Axiolateral & oblique axiolateral mandible. CR 25° cephalad.
- Mandible Submentovertical (SMV) SMV mandible. Entire mandible. IOML parallel to IR.
- TMJ Axiolateral Axiolateral TMJ. Joint space, condyle. CR 25-30° caudad.
- TMJ Axiolateral Oblique Axiolateral oblique TMJ. Joint space clear. CR 15° caudad.
- Sinuses Lateral Upright lateral. CR horizontal. Demonstrates air-fluid levels.
- Sinuses SMV Upright SMV. Vertex on IR. IOML parallel. Sphenoid + ethmoid sinuses.
Read the full chapter, free.
The free tier unlocks one complete chapter (12 lessons), 50 practice questions, and 1 sample timed exam. No credit card required.
Frequently asked questions
What does the ARRT Radiography Radiographic Procedures category cover?
Skull, Face, and TMJ is the most projection-heavy chapter on the ARRT registry. The chapter rewards rote memorization of central-ray angulation and the cranial baseline that drives each projection. Three baselines you must know cold: the OML (orbitomeatal line, outer canthus to EAM), the IOML (infraorbitomeatal line, infraorbital margin to EAM, 7° below OML), and the GAL (glabellomeatal line, 7° above OML).
How many lessons are in the Skull, Face, and TMJ Positioning chapter?
This chapter contains 12 lessons across 5 sections, plus a knowledge-check quiz at the end. The full lesson content is unlocked with a Premium subscription. The free tier includes the first chapter complete.
Is this chapter aligned with the ARRT 2025 Content Specifications?
Yes. Every chapter on this site maps directly to the ARRT Radiography Content Specifications effective 2025. This chapter falls under the Radiographic Procedures domain of the official ARRT exam blueprint.