OMR Flashcards
What makes up an X-ray film?
Emulsion Base
What is the emulsion component of the x-ray film?
Consists of * Photon Sensitive Silver Halide Grains * Suspension vehicle
What is the X-ray sensitive part of the X-ray film?
Silver Halide Grains
What happens to the silver halide grains when x-rays hit them?
A conformation change occurs which will expose an image during development ** chemically altered
What is the base component of the X-ray film?
Plastic supporting material
When the silver halide is chemically altered it creates a ____ _______.
Latent image
What makes up a film packet?
Lead foil backing (only on back side) Paper wrap Dental Film
What is the purpose of the lead foil backing?
To absorb stray x-rays
The bump on the film must always be pointing: away or towards the source of radiation?
Towards
The bump on the film should be orientated apically or coronally?
Coronally
The bump on the packet should be oriented: away or towards the source of radiation?
Away - this is the side o the film packet that has the lead foil
If the lead foil is oriented towards the source of radiation what can happen on the film?
The film will have crinkly pattern from the lead foil when developed
Size 0
Pedo
Size 1
Adult anterior
Size 2
Adult posterior
Size 3
Long posterior
Size 4
occlusal
The film speed depends on what?
The size of silver halide crystals
Faster the film speed the ______ the size of the silver halide crystals
Larger - the larger the crystals the more likely they are to be struck by an x-ray. Requires less radiation
Slower film speed the ______ the size of the silver halide crystals
Smaller - image is less grainy but requires more radiation to hit all of the small crystals
What is the silver halide chemically altered to?
Metallic silver compound
what is the purpose of the intensifying screens in the cassettes?
To use less radiation. Contains earth metals - once exposed by an X-ray the screen releases more photons to expose the film
What is a downside to cassettes?
Decreased definition. Panos’ should not be used for diagnostic measures
What is radiographic density determined by?
By the number of photons that strike the film’s emulsion layer converting silver halid crystals to metallic silver.
What does the metallic silver do?
Prevents the transmission of light through the film.
What influences the radiographic density?
mA
kVp
exposure time
focal spot to film distance
subject density
subject thickness
What is a grid?
Lead strips staggered with radioluscent material
* Helps filter x-rays through to expose the cassette
* incorporated in the cassette case or separate screen
** REDUCES SCATTER (compton, coherent) - reduces fog on radiograph **
what steps are involved in processing an x-ray film?
- Developer
- Wash
- Fixer
- Wash
- Dry
What occures to the film when exposed to the developer?
Converts chemically changed (altered) silver halide crystals into metallic silver grains that cover the film.
What happens during the was steps?
rinse for 30 sec
removes developer or fixer
What happens when exposing the film to fixer?
Removes undeveloped silver halid crystals.
Hardens and shrinks the emulsion layer
When an xray is emitted from the source of radiation it will pass through material or get absorbed by material (radiolucent - radiopaque). The xrays that pass through the material strike the emulsion layer of the film and alter the structure of the silver halide crystal. Where the xrays were absorbed in the material the silver halid crystals remain unchanged. When developing the changed silver halide crystals will be converted into silver metalic grains that remain on the film - the creates the darkness on the image. The unchanged silver halide crystals will be washed off during fixation and the fill will be lighter colored in that region.
Does the metalic silver grains create the dark or light portion of the image?
Dark
Why is the safelight a infared light?
low energy - will take a long time to actually convert a silver halid crystal
For every _____ degrees celsius icreas in temperature the rate of reaction ________?
10
doubles
What are the advantages of manual processing?
Most economical
Produces the best radiographs
What are the disadvantages of manual processing?
Most time consuming
What are the advantages of automatic processing?
Most efficieent film processings
Faster than manual
Produces dry films
What are the disadvantages of autmatic flim processing?
Expensive
Do you drain the chemicals down the drain?
NO!
Recyle
What are the advantages of digital xrays?
Lower patient exposure (reduces by 80 - 85% compared to D-speed film)
Faster
More eco-friendly
Easier storage of images
Can be easily sent to another doctor
Easy retrieval
Enalarge and vary image density
Easy to display radiographs
High resolution vs High Contrast
The average grayscale of 4 adjacent pixels in a high resolution image is assigned to create one pixel in a high contrast image
Pixels:
4:1
What are the disadvantages to digital x-rays?
Cost of equipment
Damage to sensors
Uncomfortable sensors
Loss of image
NOT AS FINE AN IMAGE - if film is ideally processed
Flim with small grain that is well developed will have the best image.
T or F
True - but requires more radiation.
What type of digital xray is the sensor?
Direct - directly connects with the computer and displays the image
What type of digital xray is the phosphor plates?
Indirect - the xray exposed a laten image that is scanned. The image is digital and stored on the computer. The Phosphor plates are reusable.
What is a photostimulable storage phosphor plate (PSP)?
Phosphor plate
What in the digital xray converts xrays to light phtons?
CSI scintillator
What do the light photons strike to create an image? (where light photons are converted into a digital image)
CMOS sensor
What format is the electronic data saved as?
DICOM format - Digital image and communication in Medicine
Digital xray constrast resolution.
The ability to distinguish different desnities in an image.
Densities are limited by noise
Human eye can detect less gray levels than computer
What is spatial resolution?
The ability to distinguish fine detail
Film - silver grains 8 microns, Digital - pixel is 20 microns –> Film has more detail
Digital systems allow enlargment of image
What is the sensor latitude?
The ability to capture a range of exposures.
* Digital and film - similar
* Phospher plate - more latitude
PSP systems allow a dose reduction of _____ compared to F speed film
50%
What are advantages of the pano compared to FMX?
Broad coverage of facial bones and teeth
Low radiation does (2.6 microSv vs 15 microSv)
Can be used in patients with trisumus or pts who cannot tolerate intraoral radiography
What are disadvantages of a pano?
Lower resolution images that do not provide fine detail
Magnification across imas is unequal
Image is superimposition of real, double, ghost images.
Requires careful visualization to decipher
Requires accurate patient positioning to avoid errors
Difficult to image both jaws when pt has severe maxillomandibular discrepancy (CLASS II)
What are some limitations of Pano?
Linear measurements are undependable
Magnification varies
Horizontal image magnification vareis from .7 to 2 times actual size.
xray beam is not orientated at right anlge to the long axis of anatomical areas or film plane
How is the xray head related to sensor in the pano?
it is located lower than sensor.
This causes:
* Foreshortening
* Elongation
What is the focal trough?
A zone that creates sharp images. Designated by the moving source (xray head) and the receptor.
Try to position pt in this trough to get a clear image.
* more narrow in anterior
* more wide in posterior
How do you get a clearer image?
Position the structure as close to the middle of the focal trough as possible.
* Structures outside of the focal trough are blurred, magnified, reduced in size, or distorted beyond regonition.
How do you position the patients anteriors into the focal trough?
Patient positioning device - bite block with a slit for anterior teeth to fall into.
Panoramic images are inherently distorted in both ____ and _____. Making linear or angular measurement highly unrelieable.
Size
Shape
What is distortion influenced by?
Beam angulation
Xray source to object distance
Path of rotational center
Position of object within the focal trough
What happens to the image when the xray source and object of interest have more distance between them?
Magnified
Elongation, foreshortening
What does a pano indicate?
overall evaluation of dentition
Fine detail and sharp image is not essential
What does a pano examine?
intraosseous pathology – cysts, tumors, infections
Gross evaluations of temporomandibular joints
position of impacted teeth
eruption of permanent dentition
dentomaxillofacial trauma
Developmental disturbances
What are ghost images?
Typically blurred, magnified, and located oposite the antomic structure at a higher level due to upard inclination of the xray beam.
How do you minimize ghost imaging?
Proper Positioning
Remove any metal
What is proper positioning during a pano?
Feet flat on the ground
Centered
Head tilted down slightly
Pt biting on bite block to separate teeth
Pt should lift tongue to the roof of the mouth - creating a tongue space
What is the Frankfort plane and what is it used for?
Line from the Tragus - Infraorbital foramen
Paralle to floor when taking pano
When a pano is underxposed what can be done to fix?
increase kVP
cannot increase exposure time on panos
Flattened panos (lack smile curve) are bad because?
The palate and ghost image of the palate obscures the tips of the roots.
How can you tell if the pts head is twisted in a pano?
One condyle may be magnified compared to another
More vertebrae show on the image on one side
What was used before cone beam imaging to capture images similar to cone beam images?
Ceph images and different positioning
What are some other extraoral radiogrpahy?
Comuted Tomography (CT)
Magnetic Resonance Imaging (MRI)
Positron Emission Tomography (PET)
An MRI uses ionizing radiation. T or F
FALSE!
What is a CT scan?
Combines the use of xray wth computer technology to produce cross-sectional images of the body
What can CT scans produce?
Clear, detailed images of all structures (bone, muscle, fat and organs) in the part of the body examined
What is cone beam imaging?
emit an xray beam shaped like a con rather than a fan (CT machines).
After this beam passes through the patient the remnant beam is captures on an amorphous silicon flat panel or image intensifier/charge-couple-devide (CCD) detector.
What component is used to measure a cone beam image?
Voxels - similar pixels except in 3D format
Why use cone beam?
Dental implants
Orthodontic planning
degenerative changes
lower widsdom teeth - nerve canal
infectios, cysts, or tumors
What is the effetive dose range for cone beam imaging?
6 - 477 microSv
What is the volume of a cone beam image?
The location and how much of the structure you are trying to get an image of.
What are the different imaging modes?
ultra low dose, low dose, high resolution
There is freedom to select the correct dosage and image quality ratio for the cone beam. T or F
True
What is an ultralow dose?
14.7 less than a pano
What is the effective does of a panoramic image>
21 microSv
Smaller voxel size requires _____ radiation.
More
* need more radiation to ensure a voxel is targeted (similar to crystals in a film)
The voxel size, FOV, and radiation dose depend on one another. T or F
True
Larger the FOV the _____ radiation is needed
MORE
If you are taking an image with a SMALL FOV at high resolution than _______ radiation is needed.
LESS - decreased FOV will influence this
If you are taking an image with a LARGE FOV with low resolution than _______ radiation is required.
MORE - FOV is larger therefore need more radiation to expose everything.
If you are taking an image with a LARGE FOV and HIGH resolution than you need ________ radiation.
MORE - both FOV and small voxels require more radiation.
Can you scan plaster models and impressions with planmeca?
YES!
What is the benefits of scanning models?
Requires less storage for orthodontics
Ortho treatment planning, follow up
Surgical guid manufacturing
What is the dose range for ultra low resolution?
14 microsSv –> 21 microSv
What are the purpose of the filters of digital radiography?
Optimize the gray scale
Eliminating “noise” through smoothing
Sharpening image detail
Extracting features (information)
How many shades of gray does a digital sensor pick up compared to the human eye?
16,000 vs 64
When decresing the brightness of a gray scale what happens to the pixels?
The grayscale of all the pixels decrease equally
There are more blacks and more whites. More grays are assigned to black or white. Will make an image more black and white looking
By adjusting the gray scale to a new white and black (more whites) what can happen to an image of a penny?
brings out the detail in the penny
Refining the gray scale will lead to more detail being observed
What are some quality controls with developing film?
Replenish xray solutions
Check temperatures
Check quality of films
Log of retakes
Check for dark room light leakage
Check exposure settings
Calibration of xray machines
