Extraoral Radiography - Skull and Cephalometric

What are the types of extraoral xrays?

Panoramic and Cephalometric & Skull Projections

Define a skill projection

Radiographs of the whole head (craniofacial skeleton)

Define cephalometric radiographs

Type of skull projection with standardized projection geometry and known magnification. It is reproducible so images can be compared over time

What are skull projections primarily used to evaluate?

Trauma, pathoses (disease processes), and sinonasal disease

Why has the use of skull projections declined?

• Inherent distortion

• Not easily reproducible

• Largely replaced by 3D modalities like CT (Computed Tomography)

When might skull projections still be used today?

• In settings where CT is unavailable or limited

• As an initial evaluation before advanced imaging

What are the three key types of skull projections?

• Occipitomental (Water’s view)

• Reverse Towne’s view

• Submentovertex (SMV) view

What are cephalometric projections primarily used for?

Orthodontic and orthognathic surgical diagnosis and treatment planning

What does cephalometry involve?

Measurement and comparison of specific points, distances, and lines within the facial skeleton

Why are cephalometric projections standardized?

To allow for consistent monitoring of growth and treatment outcomes

Name the two main types of cephalometric projections

Lateral and Posteroanterior (PA)

What is a cephalostat used for?

To stabilize the head and maintain a constant relationship between the skull, receptor, and X-ray beam

What feature on the cephalostat helps calculate magnification?

Measurement scale on the nasion pointer

How is magnification minimized in cephalometric imaging?

By using a long source-to-object distance (150 cm) and a short object-to-receptor distance (15–20 cm)

What is the typical range of magnification in the center of the cephalostat?

10–15%

Which acquisition method is faster: one-shot or scanning?

One-shot (~1 second exposure time)

What is a downside of the scanning approach?

More susceptible to motion artifacts due to longer exposure (4–20 seconds)

In lateral cephalometric projection, which side of the patient faces the receptor (in the US)?

The right side

What is the standard patient positioning for lateral cephalometric projection?

Mid-sagittal plane vertical, Frankfort plane horizontal, and maximum intercuspation

What methods reduce radiation dose to the anterior soft tissue in lateral cephs?

Wedge filter (one-shot) or increased scan speed (scanning)

In PA cephalometric projection, which direction is the patient facing?

Facing the receptor

What does a PA cephalometric projection allow you to assess?

Midfacial skeleton, mediolateral, and vertical dimensions

What is the patient positioning for posteroanterior cephalometric projection?

Mid-sagittal plane vertical & perpendicular, Frankfort plane horizontal or forehead-nose position, and teeth in maximum intercuspation