Chapter 22 Flashcards
What does panoramic radiography refer to?
Technique for producing a broad view image of the entire dentition both maxillary and mandibular on a single film. An enlongated screen film 5 or 6 x 12 is placed in a cassette and positioned extra orally.
What can a panoramic depict
Not only the teeth and alveolar bone but also the sinuses, the TMJ, the maxilla and the mandible
Panorex is best used for
- Large caries
- Examining large areas of the face/jaws
- Locating impacted teeth or root tips
- Evaluating trauma, lesions, diseases
- Assessing growth and development
Advantages of a panorex
- Depicts greater areas of diagnostic quality with less radiation than a full mouth series
- Easier for the patient to see and understand
- Less discomfort for the patient
- Since easier, less retakes
- Better time management for the dental team
Tomography
Specialized radiographic technique used to show images of structures located within a selected plane of tissue while blurring structure outside of the selected plane
It utilizes a narrow beam of x-rays to image a curved layer or slice of tissue
During tomography and rotational panoramic radiography
The tube head and film do not remain stationary as intraoral radiography but moves in relationship to each other to focus the x-ray beam on a selected layer of interest while blurring out structures outside of that layer
Where is the patients head during a panoramic
Between the tube head and the film cassette
How long will the tubehead rotate around a patients head during panoramic
15-20 seconds recording a selected image within the focal layer blurring out the spine, skull, etc
These are always opposite of each other to create a perpendicular angle for the x-ray beam to film
Tube head and cassette
Rotational centers
The axis on which the tube head and the cassette roatate is the functional focus of the projection
The x-ray beam in a panoramic
Emitted from a narrow vertical slit in the tube head and is constricted to form a narrow band of radiation in the shape of a trough, this lessens the area exposed to radiation to the area wanted depicted
If the cassette is round
It rotates in concert with the rotations around the patient to keep exposing a new area of film
In a hard flat cassette
it will move to the side in concert with the other rotations to keep exposing new film
Double center rotation
The tube head and cassette rotate to the mid-line then the radiation stops until the patient is shifted then the radiation resumes along with continuation of the rotation. A split image results
Triple center rotation
Three centers of rotation are used but the sight of the x-ray beam is so efficient that a continuous image results on the film
Moving center rotation
Most modern machines fall in this category. The elliptical pattern closely matches the arc of the teeth. A continuous image is produced. The horizontal and vertical magnification are relatively constant. The elliptical pattern can be adjusted to fit most people
Projections in the horizontal and the vertical planes
do NOT have the same focus of projection
Horizontal plane
Focus is at the center of the rotation
Vertical plane
Focus is at the target in the tube head
Difference of the vertical and horizontal
Accounts for the degree of image distortion that is characteristic of a panorex
Width of the trough and the distance from the rotational center is controlled by
the speed of the moving cassette controlled by manufacturer
Width of the trough increases
when the distance is increased
Types of panorex machines
Stand up
Sit down
Flexible cassettes
Hard cassettes
What are 4 components that the different type of panoramic machines have in common
- Rotational x-ray
- Cassette holder on drum
- Head positioner guides
- Exposure control panel
X-ray tube head
The fixed vertical position is usually around 8 degrees or pointing slightly upward. The PID is collimated with a lead diaphragm in the shape of a narrow slit opening,
Where does the x-ray beam strike
From the back of the head
Cassette holder
Can be flat or a drum and rotates in front of the patient and rotates or moves to the side to advance the film into the x-ray beam as the tube head rotates
Intensifying screens
- Transfers x-ray energy into visible light
- Allows for much less radiation since intensified
- Smooth plastic almost looks like cardboard
- Coated with minute fluorescent crystals called phosphors
- When exposed to x-rays phosphors flouresce and emit blue or green light
Screen film must be placed
Between intensifying screen inside of a cassette either rigid or flexible
Blue sensitive film
Must be paired with blue light screens. This is a conventional tungstate screen where the phosphors emit blue light
Newer rare earth screen phosphors
emit green light and must also be paired with green sensitive film. The rare earth need even less radiation then blue
Head positioner guides
Most machines are equipped with a bite block or forehead rest. Side positioners or a mirror is used for determining the correct alignment of the mid-saggital plane and a chin rest to correctly locate how far up or down the arches should be positioned. Some unites have beams of light that shine on the patients face to guide the operator to correct placement of the head
Exposure control panel
Allows for the selection of the mA and kVp as recommended by the manufacturer according to size of the patient and the density of the tissues to be imaged
Why would kVp controls be adjusted up
For better penetration of larger patients or denser tissues
Why would kVp control be adjusted down
For children and edentulous patients
Exposure time
Pre-set and is usually 15-20 seconds. All machines have a dead man’s switch which means you have to hold the button down for the entire 15-20 seconds
Lead aprons and panoramics
Are used with panoramic radiographs but not with a thyroid collar. The beam will be obstructed and the film not diagnostic
Correct head positioning
MUST have correct head position to place desired structures within the focal trough. Since the trough is pre-determined, it is the operators responsibility to properly place the patient
What are the 3 facial landmarks that are important to position the patient
Mid-saggital plane
Ala-tragus line
The frankfort plane
Mid saggital plane
Imaginary line divides the patient into a right and left halves down the center of the nose assuming the parient is positioned perpendicular to the floor
Ala Tragus Line
Imaginary line from the ala of the nose (side of the nose) through the tragus (front of the ear)
The Frankfort plane
Imaginary line from the orbital ridge (under the eye) to the acoustic meatus (ear opening), When positioned correctly, the line will be parallel to the floor
Patient too far forward in the trough
Anterior teeth will be blurred and diminished in width
Patient to far back in trough
Anterior teeth are blurred and magnified
Patient head tilted or rotated
- Teeth closer to the film will appear smaller
- Teeth closer to the rotational center (farther from film) will appear magnified
Patients chin tipped to low (frankfort plane angled downward)
The image will appear as an exaggerated smile, condyles tilt upward
Patients chin is tipped up
- The image will appear as an exaggerated frown
- Usually lose condyles in the image
Patient is slumped
Radiation is trying to pass through compressed vertebrae and so widespread RO is superimposed over the anterior teeth
Patient prep errors
- Failure to remove any object made of metal
- Thyroid collar is NOT used
- Thickly padded clothing may impede tube head
- Patients must understand and cooperate by holding still and resting tongue against the palate and close lips around bite guard
