Radiology - Panoramic Radiography - Principles and Technique

Panorama Definition

an unbroken view of the whole region surrounding the observer

Tomography

image of structures lying in a predetermined plane of tissue

blurring/eliminating detail in images of structures in other planes

What is the rotation center?

the pivotal point or axis around which receptor and x ray tube rotate

Arcs of three circle

Because the curve of the jaw, the X ray tube and receptor rotate sequentially to three pivot points

uses fixed/stationary centers of rotation with high radiation dose

Continuously moving centers of rotation

As the x ray source moves behind the patient, the center of rotation moves forward along the arc (dotted line)

Where is the beam collimated for PANO?

at the x ray tube and detector

T/F: the basic principle of image formation is the same regardless of receptor?

TRUE

Functions of laser lights in Pano machine

Panoramic units have laser lights to position the patient's
dentition in the focal trough

Structures in the center of the wide, 3D curved zone

❑ Structures in the center of this zone cast sharper, well-defined images.
❑ Structures away are less clear

How do objects outside the focal trough appear?

blurred, magnified, or reduced in size
❑ sometimes distorted to the extent of not being
recognizable

The shape of the focal trough varies with what?

• Brand of equipment
• Imaging protocol

What structures are considered real images?

Structures between receptor and center of rotation

What structures are considered ghost images?

Structures between center of rotation and x-ray source

Characteristics of Ghost Images

Higher level
Contralateral
Blurred/ significantly magnified

What does less magnification result in?

-Increase Source to Object distance
• Decrease in object to image receptor distance

What does more magnification result in?

- Decrease Source to Object distance
• Increase in Object & image receptor distance

Double images

Objects that lie posterior to the center of rotation are intercepted twice by the x-ray beam. E.g.: C-spine, Hyoid, epiglottis

What does image distortion depend on?

- x ray beam angulation
- x ray source to object distance
- path of rotational center
- position of the object within the focal trough

Horizontal magnification

- depends on the position of the object within the focal trough

Magnitude

distance of the object from the center of the focal trough

What happens with a negative vertical projection angle?

objects closer to the source are projected at a higher level

Advantages of panoramic imaging

- broad coverage of facial bones and teeth
- low radiation dose
- can be used in patients with limited mouth opening or in patients who cannot tolerate intraoral radiography
- useful visual aid in patient education and case presentation

Disadvantages of Panoramic Imaging

- lower resolution images rather than intraoral
- magnification approximately 20%. Unequal magnification, making linear measurements unreliable
- image is the superimposition of real, double, and ghost images
- accurate patient positioning - errors and artifacts

Patient positioning in panoramic image acquisition

- patient should be upright
- all metallic items like glasses, earrings, piercings, partial dentures, and other jewelry are removed
- patient should stay still.

Five major positioning criteria

- mid-sagittal plane (midline)
- occlusal plane or Frankfort plane (chin position)
- anterior-posterior jaw location (bite block)
- cervical neck/spine
- tongue/lip

Mid sagittal plane or midline positioning

the plane should be perpendicular to the floor

Frankfort plane

an imaginary line connecting the infraorbital margin and the external auditory meatus

occlusal plane or frankfort plane should be parallel to the floor

Anterior-posterior position

- anterior teeth should be in the bite block groove
- in edentulous patients: chin up or similar devices can be used instead of bite block

cervical spine/neck position in panoramic acquisition

for neck extension, use gentle upward force on mastoid eminences

slumping head and hands

Lip and tongue position in panoramic acquisition

instruct patient to swallow and hold the tongue against the roof of mouth

this eliminates radiolucent shadow

Diagnostically acceptable panoramic image characteristics

- condyles completely captured perpendicular to the inferior aspect of the image
- hard palate flat and parallel to the floor
- no asymmetry between left and right rami
- even and minimal distortion of teeth
- no palatoglossal air shadow
- no spinal shadow obscuring image
- air shadow not obscuring image

NOMAD PID and backscatter shield position

NOMAD PID and backscatter shield is parallel to the XCP ring

maximum protection exists when the shield is at the outer edge of the cone, closer to the subject, and parallel to the operator

Image quality versus distance in NOMAD

Image quality may degrade as you move PID and ring away from patient.

Inverse square law

The intensity of beam is inversely proportional to the square of the distance from source

When does protection diminish for backscatter shield?

1) when the shield is not at the
outer edge of the cone.

**Use positioning kits that do not require the shield to be slid back.

2) when the shield is distanced
from the subject.

**Hold the cone close to the patient.

3) when the shield is not parallel to the operator.

**Avoid this by asking the patient to slightly tilt their head.

Optimal storage for NOMAD

The optimal storage location is cool, dry, and away from direct sunlight.

Recommendations by National Commission on Radiation Protection (NCRP)

T/F: there is no need for personal radiation monitoring with handheld x ray equipment

TRUE

** as long as the whole body effective dose to the operator is <1.0 mSc y-1

What is the position of the X ray source, image receptor, and patient's head with respect to each other in panoramic radiography?

x ray source and image receptor rotate around the patient's head

What kind of image is formed by the objects that lie between the center of rotation and the receptor?

real image

What kind of image is formed by the objects that lie between the center of rotation and x ray source?

ghost image