Sensors and Digital Imaging Flashcards
Which type of imaging is faster?
digital
Which type of imaging uses less radiation?
digital
What does the lead foil in the film do?
limit secondary scattering of radiation
What does the black paper do in the film?
sturdiness
What is a piece of film composed of?
- supercoat - thin layer of hard plastic
- emulsion - gel and Ag halide crystal
- adhesive
- base - plastic
During film processing chemicals are used to…
form elemental Ag from silver halide salt
Chemical changes in film processing are dependent on what?
time, temperature and concentration
What is a digital image?
Digital image can be conceived as a table with columns and rows, with each cell (aka pixel) being assigned a number value which is then assigned a gray intensity
How is a visual image constructed from pixels?
The composite collection of pixel values are used by a computer’s software processing ability to construct an image for visual display
What is a pixel (px)?
A px (pixel) is the smallest portion of a sensor, image or display that is capable of being recorded and then printed or displayed
What are the general steps in digital image formation?
- x-ray shadow
- shadow image detected by digital sensor
- numerical pixel values sent to the computer
- digital image on the computer screen
What are the specific steps in digital image formation?
- Pixels are electrified
- Each pixel has a pre-exposure electrical charge
- X-ray photons that make it to the sensor change the electric charge in those pixels
- The thicker/denser the body part adjacent the sensor, the less the x-photons can affect the electrical charge
- The net effect is that there is a shadow of electric charges on the sensor reflective of the thickness/density of the body part.
- Electric charge value of each pixel is read by computer chip and the electrical voltage is converted to a numerical value
- Pixel values sent to the computer for processing
- The computer assigns the gray value of each number to the location on the X:Y grid axis of the sensor
- The gray values are displayed in a visual format on a display monitor
What are the types of historic (indirect) dental digital radiography?
Flatbed scanner
Slide scanner
Digital cameras
What are the types of indirect (semidirect) dental digital radiography?
Phosphor Storage Plate (PSP)
What are the types of direct dental digital radiography?
- Charge-Coupled Device (CCD)
- Complementary Metal Oxide Semiconductor (CMOS)
What is the issue with indirect digital radiography?
Loss or alteration of information due to partial volume averaging
The first film-like sensor was introduced in ____
1994
What are the components of semidirect digital system?
- laser scanner
- PSP plate
- x-ray source
- screen monitor
- CPU, Server, or PACS
- Printer EPR PACs
What are the steps of the PSP detector?
→ X-ray
→ PSP plate coated with crystalline halide emulsion made up of BaFBrEu2+ producing a latent image of ionized phosphors
→ scanned with red laser beam
→ emits fluorescent light from excitation of valence electrons in ionized fluorophophors
→ intensified by a photomultiplier tube
→ light intensity is converted to digital data
→ expose to strong light to erase residual images by neutralizing charges in ionized fluorophophors
→ reuse
How sensitive to light are PSP plates?
less sensitive than film but more than solid state
What are the components of direct digital system?
- x-ray source
- CCD/CMOS
- digital interface cord
- Analog-to-digital converter (CCD only)
- screen monior
- CPU, server, or PACS
- printer, ERP, PACs
What is the size comparison between direct digital sensors and film/PSP?
similar in size
How wide is the direct digital sensor?
4-5 mm wide
What are the components of the digital sensor?
- plastic housing
- CSI scintillator
- Fiber Optic Face Plate (FOP)
- CMOS imaging chip
- electronic substrate
- cable
What is the CSI scintillator in the sensor?
- takes the photons and multiplies it (increases strength of signal)
- optimized for resolution and low noise
What is the CMOS imaging chip?
- has the pixels
- patented techology with cut corners
What are some drawbacks of CCD/CMOS?
- uncomfortable (don’t bend like film)
- internal active area (portion of the sensor that produces the image) is smaller
What are the types of digital sensors?
CCD (charge coupling device)
CMOS (Complementary Metal-Oxide-Semiconductor)
What are most types of digital sensors?
CMOS
What is the simplified sensor concept?
- each pixel is like a tiny battery with its charge equal to the number of electons trapped inside
- the computer records the charge in each pixel and converts it into a gray value
What is the sensor thickness sweet spot?
4-6 mm
What type of sensor is preferred?
open source
What is the pixel size/image quality for most sensors?
~ 15 µM (10-6 M)
~ 15 microns (10-6 M)
~ 15 10-3 mm
How sharp is the image quality of most sensors?
Actual – visible
- >20 lp/mm
Theoretical – calculated
- >26 lp/mm
What is the line pair resolution?
how sharp an image is or the image quality
What are the characteristics of a CCD?
● Older technology
● Require an additional power via an adjunct box
● Need additional power to convert the photon energy to an electronic digital signal
What type of digital sensor needs to go through an analog-to-digital converter box?
CCD
What are the steps of a CCD detector?
X-ray → scintillating material → light photos → silicon → electrons deposited in electron wells → transferred in a sequential manner (charge-coupling) → read-out amplifier → images on monitor
What is charge-coupling?
- pixel signals in row are transferred in sequential manner to be digitized
- CCD
What makes digital CCD detectors “slow”?
charge-coupling
What was the first type of digital sensor?
CCD
What are the steps of the CMOS detector?
X-ray → scintillating material → light photos → silicon → electrons deposited in electron wells and converted to voltage in each pixel→ smoother signal digitization → software processing → images on monitor
Which digital sensor is cheaper: CCD or CMOS?
CMOS
Which is more sensitive to X-rays: CCD or CMOS?
CCD
Which has a higher system complexity but lower sensor complexity: CCD or CMOS?
CCD
Which has a lower system complexity but higher sensor complexity: CCD or CMOS?
CMOS
What are the characteristics of CMOS?
● Newer technology
● Require less power
● Superior image quality
Which can you use less radiation because it is more sensitive: CCD or CMOS?
CCD
What is the usual bit depth for a sensor?
8-12 bit
- 8 bit (2^8) = 256 shades of grey
What is bit depth?
the number of colors (or grey shades) that a pixel is able to show
Which of these has the highest bit depth and which has the highest contrast?
A - highest bit depth
D - highest contrast
Which is better for an image: high or low contrast?
high and low contrast are good depending on what you are trying to see
What gives you more information about an object: high or low contrast?
low contrast
What type of sensors have been applied in panoramic and plain skull images?
CCD and PSP plates
Why is digital imaging appealing?
Significantly less radiation
Better image (?)
Lower costs — more net income
- reduced patient chair time
- no variable costs
- elimination of dark room
Environmentally friendly - less toxic chemicals are disposed into the sewage systems
Electronic communication improves efficiency
Rapid acquisition and storage
Image portability
What has a lesser effective dose for common exam radiographs?
FMX PSPP
FMX CCD
FMX D-speed
FMX D-speed - 388
FMX PSPP - 171
FMX CCD - 85
CCD has the smallest effective dose
What are the mathematical manipulations of image data?
- Compression
- Imaging manipulations (qualitative)
- Automated image analysis (quantitative)
- Image reconstruction
What is image processing?
Mathematical manipulation of image data
What are qualitative digital image modifications?
● Uses mathematical operations called matrix transformations
● Magnify, adjust contrast, brightness, gray scale, colors, swap black and white
What are quantitative/analytical digital image modifications?
● Measure lengths (# of pixels for length, area, circumference, etc.)
● Measure pixel values (bone, enamel, dentin, pulp, soft tissue densities)
What is compression of a digital image?
– affects image file size in memory storage
- useful for storage issues eg. “zipping” files
- actual file size is larger that stored file size
- compression is an algorithm that can shrink the file size for storage and recreate the data when retrieving the data
The file memory size of a digital image can become large due to…
– size of grid (sensor size)
- number of images
- bit depth
What are the different types of qualitative image manipulations?
➢ Edge Enhancement – sharpening filter
➢ Noise Reduction – softening filter
➢ Optimization of density/contrast
➢ Inversion of gray scale
➢ Magnification
➢ Emboss function
➢ Pseudocolor enhancement
What is image manipulation?
- are post-display mathematical algorithms that manipulate the digital signal
- the computer will change density values to predetermined numbers which then changes the image’s presentation i.e., lighter darker, etc
Does manipulating an image increase the diagnostic accuracy?
NO
What does image manipulating do?
Depend on viewer preference
Make the images subjectively more appealing
DO NOT increase the diagnostic
accuracy
What is good about altering the brightness/contrast?
The brightness and contrast adjustments are done together to subjectively find the “best” combination of brightness and contrast to highlight the clarity of the structures in the image
What can “softening” or noise reduction do to an image?
May degrade or remove important diagnostic informatio
What does sharpening or edge enhancement do to an image?
Remove low-frequency noise; increases image contrast
Exaggerate the contrast difference between adjacent pixels; to increase contrast, all pixel values are stretched; the dark shades become darker and the light shades become lighter
Enhances local contrast and makes edges sharper to diagnose caries, restoration fit, and fractures
-can simulate disease
What is magnification of an image?
Enlarge a specific area till the biggest detail
What is the emboss function (inactive)?
- Applies a three dimensional effect to the image
- Could be useful in presentation situations
What are the different types of analytical/quantitative automated image analysis?
- Length
- Angles
- Bone Density
- Area
- Circumference
- Etc…
What is image reconstruction?
Data is utilized by other software programs and produces different image presentations
