digital image capture Flashcards
What is A Computer?
Data processor according to a set of instructions (a Program)
What kind of data?
Numbers
What does Digit/Digital mean?
It comes from Latin digitus which means “finger”
Computers in Diagnostic Imaging
- Modern Computers process numbers on a binary base 0 / 1
- Corresponds to off / on of trillions of electronic switches : Transistors
- bit : Binary digit ( base 2 number, from the Latin bini = two)
Digital Imaging & Radiography
Computers in Diagnostic Imaging
Painting by Numbers : Digital Image
Pixel (Picture Element) corresponds to tissue Voxel (Volume Element) within the patient’s body
Numerical value displayed as shades of grey proportional to X-ray attenuation
A digital image is a matrix of many small elements, or pixels.
Each pixel is represented by a numerical value. In general, the pixel value is related to electrical signal measured in a certain location . The Numerical value define the brightness (shade of grey) of each pixel when the digital image is converted into an analogue image for display and viewing on a Monitor.
Generally, at the time of viewing, the actual relationship between a pixel numerical value and it’s displayed brightness is determined by the adjustments of the window control as discussed in other modules.
A digital image is a matrix of many small elements, or pixels.
Shades of grey are assigned to pixel values.
High density tissues (such as bone) are displayed as bright pixels compared to low density tissues (dark pixels)
Advantage of Digital Radiographic Systems
Store Images into Digital Archives
Advantage of Digital Radiographic Systems
Easy and fast distribution to local and remote viewingworkstations
Easy and fast distribution to local and remote viewingworkstations
Post-process images to aid visualization of anatomy and pathology
Less requirement to repeat
Lower Doses
Speedy availability and distribution of final image
CR Overview
Does not use films
Store Image on Photostimulable Phosphor Plate (PSP) also known as “cassettes”
Visualization and Acquisition happen at different times
Based on physical process of Photostimulated Luminescence (PSL)
image acquisition
cr image reader
image display
image acquisition
- captures and stores radiographic image in reusable imaging plate
cr image reader
- image is developed in a digitiser
image display
- image is displayed on the monitor
cross section of cr plate
protective layer
phosphor layer
anti-halo and reflective layer
base
backing layer
CR – Computed Radiography
Electron excited by X- Ray trapped in semi stable Higher Energy Level
”X-ray photons are absorbed by the phosphor layer, and the phosphor electrons become ‘excited’ and are raised to a higher energy level, where they can stay trapped in a semi-stable higher-energy state.”
The trapped electrons represent a latent image in the phosphor plate in the form of ‘stored energy’.
CR – Computed Radiography
Trapped Electrons form latent image(stored energy) with short life and will spontaneously decay
”X-ray photons are absorbed by the phosphor layer, and the phosphor electrons become ‘excited’ and are raised to a higher energy level, where they can stay trapped in a semi-stable higher-energy state.”
The trapped electrons represent a latent image ( in the phosphor plate in the form of ‘stored energy’. ) development
theinvisiblechangein aradiographicdetector/platethatiscausedbyx-radiationorlightandismadevisiblethrough the acquisition process in computed and digital (direct) radiography modalities.
CR – Computed Radiography
LATENT IMAGE:
theinvisiblechangein aradiographicdetector/platethatiscausedbyx-radiationorlightandismadevisiblethrough the acquisition process in computed and digital (direct) radiography modalities.
CR – Computed Radiography
Laser stimulate electrons to escape
energy released in form of Light
” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.
The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light
The emitted light intensity is proportional to the original X-ray intensity.
CR – Computed Radiography
Exposure
Latent Image
Readout
” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.
The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light
The emitted light intensity is proportional to the original X-ray intensity.
” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.
The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light
The emitted light intensity is proportional to the original X-ray intensity.
CR – Computed Radiography
Light detected by Photomultiplier tube
A/D Convertor process data to a file that can be displayed on a monitor
Exposure to Bright Visible light erase plate (reusable)
The light energy is detected and the signal is digitised. These data are processed digitally to produce a visible diagnostic image on a monitor. The phosphor plate is then ‘erased’ with a bright white light to remove any remaining trapped electrons, and the plate is then ready for the next examination
Photomultipliertubes (photomultipliers orPMTsfor short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light.
CR – Computed Radiography
Plate Reading
Stimulation (Laser) and Emission lights have different wavelength so they can be filtered
The spectra of the stimulating and released light used in the phosphor screens are chosen for a very specific reason. Because these peaks are separate, they enable the stimulating laser light to be filtered from the phosphor screen luminescence.
CR – Computed Radiography
Sampling :
Asampleis adigitalrepresentation of an analog signal
Sampling pitch,or distance between the sampling points
Sample Frequency: How often the analog signal is reproduced in digital format
CR – Computed Radiography
Sampling :
Asampleis adigitalrepresentation of an analog signal
Sampling pitch,or distance between the sampling points
Sample Frequency: How often the analog signal is reproduced in digital format
DR – Direct Radiography
DR Overview
DR imaging combines image capture and image readout (versus two steps of CR)
Self-scanning readout mechanism via an array detectors that convert the varying-ray intensities into proportional electronic signals
DR images available almost instantly after exposure
DR Overview
DR Receptors more fragile and much more expensive than CR
Flat Panel Detectors are constructed in layers to convert X- Rays to Electrical charges
Read-out , Digitalization and storage integrated
Direct Radiography
The energy of a photon creates an electron/hole combination (or Charged Couple )within the depletion layer which allows current to flow across the terminals of the Photodiode
Very Fast switch activated by Light
Aphotodiodeis a semiconductor device that converts light into an electrical current. The current is generated when photons are absorbed in thephotodiode.
Direct Radiography
Do you remember what is called an array of photo diodes?
CCD (Charged Couple Device) are made up of a two dimensional array of photo diodes that change light into a grid of different amounts of electrical charge.
Each photodiode represent a pixel in the image, the charge created is proportional to the amount andof lightfalling on it.
Shift Register
TheShift Registeris a type of sequential logic circuit that can be used for the storage or the transfer of binary data.
Shift Register
TheShift Registeris a type of sequential logic circuit that can be used for the storage or the transfer of binary data.
DR Technology
INDIRECT CAPTURE DR (Scintillator)
Phosphor (Cesium Iodide) + Charged Couple Device
OR
Phosphor (Cesium Iodide) + Photodiode ASi (Amorphous Silicon) +Thin- Film Transistor TFT
DIRECT CAPTURE DR
Amorphous Selenium + TFT
DR Technology- INDIRECT CAPTURE - Scintillator + CCD
LAYERS :
Scintillator Phosphor (Cesium Iodide)
Fiberoptic (Optical Coupling)
CCD (Convert light into electronic signal)
Glass Substrate
DR – Direct Radiography
DR Technology- INDIRECT CAPTURE - Scintillator + TFT
LAYERS :
Scintillator Phosphor
(Cesium Iodide)
Photodiodes (A-Silicon)
TFT
Glass Substrate
TFT:
Thin Film Transistors array
Captures Charges and transmits them to the ADC
DR Technology DIRECT CAPTURE DR Amorphous Selenium + TFT
Layers
Amorphous Selenium (Photoconductor )
TFT
Converts X-Ray into Electrons to create Image
Better Resolution than Indirect (No light Scattering)
DR – Direct Radiography
After signal is converted by the Analogue Digital Converter (ADC)
This is passed via cable or wireless connection to the modality computer
The digital data is then stored as a digital image file
