Digital Imaging Flashcards
Advantages of computer use in radiography
Generators more precise Increased diagnostic power Increased efficiency Transmission of images Increased storage capacity
Analog
Continuously variable signal (electric currents)
Digital signal
Signal converted to digital form and then used in a display or computation. Defined quantities of current.
Easier to read-more precise
Integrated circuit chip
Small semiconductor chip in which millions of circuit elements are placed.
Allows computers today to be much smaller than 1st and 2nd generation
Software
Invisible
Instructions (programs)
Soul of computer
Hardware
Visible
Nuts and bolts
Body of computer
Binary number system
Number system computers use to operate. 0s and 1s.
Each single binary number is called a bit
Computers are rated in terms of
Byte memory
Systems software
User friendly. Make it easy to operate
Ex: windows
Applications software
Carry out user function.
Apps.
Ex: word
Computer language
Allows us to write programs in language similar to ours
Ex: java
Processing of computer hardware
Electronic circuitry that does the actual computations and the memory that supports this
Central processing unit or microprocessor
Acts as a nucleus to computer
Contains control unit and logic unit
Control unit of CPU
Directs incoming data to arithmetic or memory unit
Interprets users program instructions in proper sequence
When task complete transfers information to output device
Logic unit of CPU
Performs logic and numeric calculations
Bus
Connects control unit and arithmetic unit and all other components during processing
System clock
Determines speed of computer
GHz, MIPS
Main memory/storage memory
Long term storage
Stores programs and data files
Active memory or random access memory (RAM)
Memory replaces old with new info
Short term
ROM
Read only memory
Operating instructions
Rarely changed
RAM
Random access memory
Temporary storage during use
Gets changed
Optical disks
Stores digital data in mirrored surface with laser light
Disk drive
External hard disc drive
Stack of discs that store data magnetically
Take them from place to place
Used for backing up computer
Solid state storage devices
Store data using flash memory
Type of erasable programmable read only memory (EEPROM)
USB flash drives
Also use flash memory
Input
Allows us to put in information
Keyboard, mouse, trackball, light pen, touchpad, scanner, fax machine, imagine system, audio and video devices, voice recognition, sensors, biological input devices (thumb print)
Output
Allow the computer to give us information
From memory to storage or user.
Display screen, printer, speaker, laser camera/processor
Communications
From one computer to another
Requires modem if communication lines are analog
Information can be transferred through:
Electric cable
Electric wire
Atmosphere
Fiber optic cable
Information can be transferred AS:
Electric current, light, radio frequency, digital bit system
What is a digital image?
Image that has been converted to numbers
Image is displayed as a matrix of intensities that correlate to numerical values
These numerical values can be stored and manipulated by computer
Fourier transformation
Mathematical method used to create computerized medical images
Allows digital and computerized imaging to be
Matrix
Arrangement of columns and rows of cells that make up the image
The larger the matrix
The greater the spatial resolution
Pixel
Individual cells of matrix
The smaller the pixel size
The greater the spatial resolution
Pixel density
Number of pixels per unit area
For a given FOV, pixel density increases, pixel size decreases, increase spatial resolution
Pixel pitch
Distance from the center of one pixel to the center of the adjacent pixel
Decreased pixel pitch
Increased spatial resolution
Voxel
Volume element
3D volume of tissue that is represented by a certain pixel
Pixel value
Numerical value of each pixel
Lower number means white/bright
Higher number means darker
Bit depth
Number of shades of gray possible for a system to acquire and display.
Increased bit depth
Increased contrast resolution
Digital imaging processing
3 steps:
Scanning
Sampling
Quantization
Sampling frequency
Frequency at which the analog signal is sampled
CR: increased sampling frequency=increased spatial resolution=decreased pixel pitch
Nyquist frequency
Sampling frequency must be greater than 2x the signal frequency to avoid aliasing (Moire effect)
Histogram
Graphic display of pixel values of a given digital image
Automatic rescaling
Process employed during histogram analysis that maintains consistent image brightness and contrast
Exposure data recognition
Ability of a digital system to identify raw background exposure field so that data outside o the anatomy may be excluded from histogram analysis and exposure indicator calculations
Window level
Image brightness
Sets mid point of the range of densities visible in the image
Window width
Controls image contrast
Increased width longer scale of contrast
Low pass filtering
Smoothing
Used to remove high frequency noise
Band pass filtering
Selects a band of frequencies to delete or amplify
High pass filtering
Edge enhancement
Convolution
Modifying pixel values to enhance of suppress visual characteristics of an image
Reconciliation
Returning pixel value to original level
Silicon TFT flat panel imaging system
Scintillator-CSI or gadolinium oxysulfide conveys X-ray to light
Silicon-concerts light to electron
TFT-determines when charge will be released from capacitor. Releases electrons in orderly fashion
ADC-converts electrons to number value
Advantage of silicon TFT
High DQE which decreases patient dose
Disadvantages of silicon TFT
Loss of resolution from light divergence of scintillation phosphor
CCD
Scintillation- CsI or gadolinium oxysulfide converts X-ray to light
CCD-converts light to electrical signal and sends to computer
ADC-converts electrons to number value
Advantage of CCD
100% fill factor, 85% light conversion efficiency
Disadvantage of CCD
Pixel size, a lot of heat produced high power requirements
CMOS complimentary metal oxide semiconductor
Scintillator-concerts X-ray to light
CMOS-converts light to electrons and sends to computer
ADC-confers electrons to number
Advantage of CMOS
Smaller and faster than CCD, lower power consumption
Disadvantage of CMOS
More susceptible to noise
Selenium TFT
Selenium-charged prior to exposure concerts X-rays to electrons
Electrodes collect electrons
TFT sends signal to computer in orderly fashion
ADC-Change electrons to numbers
THIS IS THE ONLY DIRECT APPROACH
Advantage of selenium
No light conversion, no light divergence which means increased resolution
Disadvantage of selenium
Lower DQE than silicon, need to use more dose
