Imaging Flashcards
Different types of dental film & their qualities?
D speed = slower, more radiation, better image quality
F speed = faster, less radiation, loss of image quality (still diagnostic)
What are the contents of the film packet?
- packet with opening tab
- lead foil
- black light proof paper
- film
Purpose of lead foil in film?
- protect from back scatter radiation that can cause a re-exposure
In a cross-section of film what is it composed of from outside in?
- supercoat: thin layer hard plastic
- emulsion: gel & silver-halide crystal
- adhesive
- base: plastic
The chemical changes in film processing are dependent on what factors?
- time, temperature, & concentration
What is a pixel?
“picture element”
- smallest portion of sensor/image capable of being recorded & then printed/displayed
What are the 4 general steps in digital image formation?
- x-ray shadow
- shadow image detected by digital sensor
- numerical pixel values sent to computer
- digital image on computer screen
How are numerical values assigned to each pixel?
- pixels are electrified by x-ray
- each pixel has pre-exposure charge
- x-ray photons make it to sensor change the charge
- the thicker/denser object, the less photons can affect the charge of the pixel
- net effect is that there is a shadow of electric charges on the sensor reflective of the thickness/density of the body part
What is meant by digitization?
electrical voltage is converted into numerical value by computer
How is the digital image displayed on the computer screen?
- computer assigns gray value for each number to the location on the XY grid axis of the sensor
- gray values are displayed in visual format on monitor
Example of semi/indirect dental digital radiography?
PSP: phosphor storage plate
Examples of direct dental digital radiography?
CCD: charge coupled device
CMOS: complementary metal oxide semiconductor
What is the PSP plate coated with?
- crystalline halide emulsion: BaFBrEu2+
–> Europium doped barium fluorobromide
What is the purpose of doping the PSP plate in europium?
holds the charge
Describe the steps of the PSP detector?
- x-rays hit PSP plate coated in BaFBrEu2+ producing a latent image of ionized phosphors
- PSP scanned with red laser beam
- emit fluorescent light from excitation of valence electrons in ionized fluorophosphors
- intensified by photomultiplier tube
- light intensity converted to digital data
- expose to strong light to erase residual images by neutralizing charges
- reuse
T/F PSP plates are sensitive to light?
true, but not as sensitive as film (up to 10s)
What type of solid state sensor requires analog to digital converter?
CCD: charge coupled device
What is the function of the analog to digital converter?
electrical signal from sensor must be read out here before sent to computer
What is the size comparison of film, PSP, and digital sensors?
all similar in size because based off film
What is the minimum thickness a digital sensor can have?
4 mm (rigid & not as comfy in mouth)
What is the scintillator function in solid state sensors?
optimized for resolution & low noise
- cesium iodide
What are the components of digital sensors?
- electronic substrate (ceramic)
- imaging chip
- fiber optic face plate (xray filter)
- CSI scintillator
What are the drawbacks of direct sensors?
- rigid & uncomfortable
- actual image capturing area is less than external size (78%)
What is the pixel size in solid state sensors?
15 uM2
T/F solid state/direct sensors have greater resolution than film?
false: but still diagnositc
What is the main difference between CCD & CMOS?
CCD requires an additional/adjunct power box to convert photon energy into electrical digital signal
What is the sequence of the CCD detector?
- x-ray
- scintillating material
- light photons
- silicon
- e- in wells of pixel
- pixel signals transferred in sequential manner (charge-coupling) to be digitized
- read-out amplifier
- images on monitor
What is the sequence of the CMOS detector?
- x-ray
- scintillating material
- light photons
- silicon
- e- in wells of pixels & converted to voltage
- smoother signal digitization
- software processing
- images on monitor
Which is faster & efficient at transferring electrical signal into digital image?
CMOS
Which has greater power consumption? CCD or CMOS
CCD
Which is more sensitive to x-rays? CCD or CMOS
CCD (positive)
Which has higher noise? CCD or CMOS
CMOS
Which has a simple readout? CCD or CMOS
CMOS
What are the pixel signals in CCD & CMOS?
CCD: e-
CMOS: voltage
What is the chip output for CCD & CMOS?
CCD: voltage (analog)
CMOS: bit (digital)
What is the system complexity & sensor complexity of CCD?
high / low
What is the system complexity & sensor complexity of CMOS?
low / high
Is CMOS or CCD a new technology?
CMOS
What is a bit?
depth of colors / gray shades that a pixel can show
aka: number of shades of gray
How do you calculate the number of shades of gray?
2^bit
What is the ideal bit range & why?
8-16 (any higher and we just cannot see those extra shades)
Why is digital imaging appealing?
- significantly less radiation
- better image?
- rapid acquisition & storage
- image PORTABILITY
- lower cost (less chair time, no additional costs for equipment, no darkroom)
- environmentally friendly
What type of digital image modification describes the use of mathematical operations called matrix transformations?
qualitative
What type of digital image modification describes measuring lengths / # of pixels for length, area, value, etc.?
quantitative/analytical
What are examples of qualitative modifications?
- magnify
- adjust contrast
- brightness
- grayscale
- colors
- swap b&w
What are post-display mathematical algorithms used to modify the digital signal?
image manipulations/enhancements
T/F imaging manipulations can increase the images diagnostic accuracy?
false
Is noise reduction used in dental radiographs?
NO, may degrade or remove important diagnostic information
What describes making dark shades darker and light shades lighter?
sharpening
Is the sharpening/edge enhancement feature used in dentistry?
NO, can simulate disease / change density pattern completely
What does penumbra mean?
unsharp
How does the size of the radiation source (focal spot) affect the sharpness?
the smaller the focal spot, the sharper the image // less penumbra
–> due to less xray photons
How does source to object distance affect image sharpness?
The farther the object away from the xray source the sharper the image
–> less divergent photons // more parallel
What factors can we manipulate to increase sharpness?
- source-to-object (length of cone)
- object-to-receptor (place receptor close to tooth)
How does object-to-receptor distance affect image sharpness?
the closer the object to the receptor, the sharper the image
–> less divergent photons due to less time to diverge away from tooth
What are the 2 rules to minimize magnification?
- source to object distance
- object to receptor distance
How does the source to object distance affect magnification?
the farther the object from the source the less magnification
How does the object to receptor distance affect the magnification?
The closer the receptor to the object the less magnification
What term describes unequal magnification or variance from true shape?
distortion
What factors affect distortion of the image?
- alignment of receptor, object & beam
What are the 2 rules to minimize distortion?
- beam perpendicular to object & receptor
- object & receptor should be parallel
How does foreshortening occur?
- tooth is not parallel to receptor & the beam is perpendicular to the receptor
How does elongation occur?
- tooth is not parallel to receptor & beam is perpendicular to tooth
What technique do we use at UMKC for periapical radiography?
paralleling
What length cone should you use with the paralleling technique?
long
What is the alternative method for taking PA radiographs?
bisecting angle
What length cone should you use for the bisecting angle technique?
short
What is the limitation of the paralleling technique?
maxilla is curved & cannot always get receptor close to tooth (object to receptor distance increased)
How do we compensate for the curvature in the maxilla with the parallelling technique?
we use a long cone (source to object distance increased)
What can occur if the beam and receptor are not aligned properly?
cone cut
How does the bisecting angle technique work?
- tooth & receptor are not parallel
- beam is directed perpendicular to the bisecting line
How many radiographs compose a full mouth series (FMS)?
18 or 20
What are the 2 methods for radiographic localization?
- right angle
- tube shift / SLOB
How to do the right angle method for localization?
- straight on PA
- cross-sectional occlusion
How to do tube shift technique?
- straight on PA
- shift tube M or D
- if object moves same direction as shift then it is lingual
- if object moves opposite direction as shift then it is buccal
