Panoramic Radiography: Principles & Technique Flashcards
What is the definition of panorama?
An unbroken view of the whole region surrounding an observer
What is tomography?
- “Slice image”
- Image of structures lying in a predetermined plane of tissue, blurring detail in images in other planes
What happens when a panoramic image is taken?
X-ray source and receptor rotate synchronously around the stationary patient
What is the pivotal point or axis around which the receptor and x-ray tube rotates?
Rotation center
To capture the curve of the jaw, what must the X-ray tube and receptor do?
Have to rotate sequentially about three pivot points, called fixed rotation
Does a fixed center of rotation have a high or low radiation dose?
High
Do we currently use a fixed center of rotation in clinic?
No, not a modern technique
What does a continuously moving center of rotation mean?
X-ray source moves behind the patient, the center of rotation moves along the arc
What X-ray tube head is used in a panoramic unit?
IO tube head
What is the function of the collimator?
Restrict x-ray beam to reduce exposure
Where is the beam collimated in a panoramic machine? 2 answers.
- X-ray tube
- Detector
Is the image formed sequentially?
Yes
Does the basic principles of image formation change when using films or digital CCD/PSP?
No
The purpose of laser lights on a panoramic unit is to position the patient’s dentition where?
In the focal trough
What is the focal trough?
Wide, 3D curved zone where structures in the center of it will be sharp well defined images
How do structures appear outside of the focal trough?
Blurred, magnified, or reduced in size
What does the shape of the focal trough vary with? 2 answers.
- Brand of equipment
- Image protocol/what type of image you are taking
What are structures between the receptor and center of rotation called?
Real images
What are structures between the center of rotation and the x-ray source called?
Ghost images
How can ghost images appear? 3 answers.
- Higher level
- Contralateral
- Blurred/significantly magnified
How do you decrease magnification? 2 answers.
- Increase source to object distance
- Decrease in object to image receptor distance
How do you increase magnification?
- Decrease source to object distance
- Increase in object and image receptor distance
What are many ghost images from?
Normal anatomic structures
Can ghost images of normal anatomic structures be a normal finding?
Yes
When are double images created?
Occurs when objects lie posterior to the center of rotation and are intercepted twice by the x-ray beam
What are 3 anatomic structures that create double images?
- C-spine
- Hyoid
- Epiglottis
What are four image distortion factors that can occur in pan images?
- X-ray beam angulation
- X-ray source to object distance
- Path of rotational center
- Position of the object within the focal trough
What does horizontal magnification depend on?
Position of the object within the focal trough
What causes vertical projection angles?
Negative angulation, objects closer to the source are at a higher level
What are a few advantages of a pan? 4 answers.
- Broad coverage of face/teeth
- Low radiation dose
- Good for patients who are intolerant to intraoral radiography
- Patient education and case presentation
What are a few disadvantages of a pan? 4 answers.
- Lower resolution
- Unequal magnification, no linear measurements
- Real, ghost, and double images
- Patient position can lead to errors/artifacts
How should a patient be positioned for a pan? 3 answers.
- Upright
- All metalic items removed
- Stay still
What are the 5 major positioning criteria?
- Mid-sagittal plane
- Occlusal plane/Frankfort plane
- Anterior posterior jaw on bite block
- Cervical spine
- Tongue and lips
What is the mid-sagittal plane of a pan?
Plane should be perpendicular to the floor
What is the occlusal or Frankfort plane of a pan?
Imaginary line connecting the infraorbital margin and the external auditory meatus, should be parallel to the floor
What is the canine lines of a pan?
Imaginary line connecting the inner cactus of the eye and canine
What is the anterior-posterior plane of a pan?
Bite block position, anterior teeth should be in groove to maintain the focal trough
What is the cervical spine/neck position of a pan?
Proper neck extension, using dental upward force on the mastoid eminences
What does slumping cause in a pan image?
Ghost image
What is the lip and tongue position of a pan?
Patient should swallow and hold the tongue against the roof of the mouth
What are the 7 diagnostically acceptable pan image requirements?
- Condyles are completely captured and are perpendicular to the inferior aspect of image
- Hard palate is flat and parallel to floor
- No asymmetry between left and right rami
- Even and minimal distortion of teeth
- No palatoglossal air shaddow
- Spinal shadow not obscuring
- Aur shadow not obscuring
What must all operators wear when using a hand held x-ray device, according to the VA Department of Health?
Protective lead apron
How should you hold a NOMAD PID?
With both hands and have backscatter shield parallel to floor
Image quality will ____ as you move the PID and ring away from the patient.
Degrade
When is the backscatter shield most effective? 3 answers.
- Shield is at outer edge of cone
- Close to subject
- Parallel to operator
What does the inverse square law state?
Intensity of beam is inversely proportional to the square of distance from source
