PA AXIAL PROJECTION: SKULL SERIES | HAAS METHOD

HAAS METHOD SKULL SERIES

Pathology Demonstrated:

• Occipital bone, petrous pyramids, and foramen magnum, with dorsum sallae and posterior clinoids in its shadow, are shown.
• This is an alternative projection for patients who cannot flex their neck sufficiently for AP axial (Towne). It results in magnification of the occipital area but results in lower doses to facial structures and the thyroid gland.

This is not recommended when the occipital bone is the area of interest because of excessive magnification.

Tecnical Factors:

• IR size - 24 x 30 cm (10 x 12 inches), lengthwise
• Moving or stationary grid
• 70 to 80 kV range
• Small focal spot
• mAs 20

Patient Position:

• Remove all metallic or plastic objects from the patient's head and neck. Take radiograph with patient in the erect or prone position.

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 exist (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 1 1/2 inches (4 cm) superior to the nasion.
• Center image recptor to projected CR.
• Minimum SID is 40 inches (100 cm)

Collimation:

• Collimate to the outer margins of the skull on all sides.

Respiration:

• Suspend respiration.

Radiographic Criteria in PA Axial Projection | Haas Method:

Structure Shown:

PA Axial

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

Position:

• No rotation is evident, as indicated by bilateral symmetric petrous ridges.
• Dorsum sallae and posterior clinoids are visualized in the foramen magnum, which indicates correct CR angle and proper neck flexion and extension.
• No tilt as evidenced by correct placement of anterior clinoids within the middle of the foramen magnum.

Collimation and CR:

• In Haas Method the entire skull is visualized in the image with the vertex near the top and the foramen magnum and mastoid portions near the bottom.
• Collimation borders are visible to outer margins of skull.

Exposure Criteria:

• Density and contrast are sufficient to visualize occipital bone and sellar structures within foramen magnum.
• Sharp bony margins indicate no motion.