This document provides an overview of computed radiography (CR) and digital radiography (DR). CR uses an imaging plate that captures x-ray data, which is then processed to produce digital images. DR directly converts x-rays to digital signals using detectors like selenium or scintillator crystals. Both produce digital images but DR has higher image quality and requires less time as there is no imaging plate development step. While DR systems have higher costs, the digital format allows for improved image processing and long-term storage compared to conventional radiography.

1. COMPUTED RADIOGRAPHY (CR)&
DIGITAL RADIOGRAPHY(DR)
DR-VISHAL
JUNIOR RESIDENT
RADIO-DIAGNOSIS
RKCH RAIPUR

2. OVERVIEW
• INTRODUCTION
• COMPONENTS
• PRINCIPLE
• WORKING
• ADVANTAGES
• DISADVANTAGES

3. DIGITAL X-RAY TECHNOLOGY
• 1] COMPUTED RADIOGRAPHY
• 2] DIGITAL RADIOGRAPHY

4. COMPUTED RADIOGRAPHY
• It is the digital replacement of conventional xray film radiography
• it is the process of capturing radiogrphic data from a conventional xray
machine and processing that data to produce high quality radiographic
images
• For exposure an imaging plate (IP) is placed in a casette instead of a
piece of film [filmless system]
• The IP captures and “stores” the x-rays
• The image is “developed” in a CR reader instead of a film processor.The
CR reader extracts information stored in the plate and produces a digital
image

5. Basic modules of CR
• Casette with IP
• ID Tablet
• Preview & ID station
• Digitizer
• Processing Server
• Laser Camera

6. CASSETTE
• Light weight plastic backed by
aluminium.
• Front panel made of low
attenuation carbon fiber
• Back panel contains lead foil to
protect the plate from
backscatter
• Back panel also contains chip to
record patient demographic
information

7. IMAGING PLATE
• Made up of multiple layers
1. Protective layer-plastic made-
protects phosphor layer
2. phosphor layer-photostimulable
phosphor that traps electrons during
exposure
3. Anti halo and reflective layer-reflects
light to reader
4. Conductive layer-absorbs light as
well as any electrical charge
5. Backing layer-polyster made- gives
strength
The phosphors are madeup from bariumfluorohalide
crystals.Also a metal named Europium(Eu) is doped into
those crystals which helps the phosphors in trapping
electrons [by making defects in the crystals]

8. PRINCIPLE & WORKING
• When the phosphor is exposed to radiation,it
absorbs the radiation and stores the energy.Later
when it is exposed by a different light source,it
gives luminescence
• When IP is exposed to radiation,the divalent Eu
atoms gets oxidized into trivalent EU ion with
release of e- in valence band which later move to
conduction band and later trapped at the F
centres in the forbidden zone.
• When IP is scanned by red laser light,the F centres
absorbs energy and transfer it to the e-
• the electrons move from conduction band to
valence band with emission of blue-green light
• finally e- joins with trivalent Eu and converted into
divalent Eu

9. • The Blue green light is collected by the PHOTOMULTIPLIER TUBE (PMT) which amplifies
the signal and gives the output electronic signal which is fed to computer for further
processing.
• It takes ~110 sec to process each casette.
• The phosphor will not give up all the trapped electrons in the first laser light exposure.It
will retain some amount of trapped electrons
• Hence, it is exposed to a very bright light source, which moves all the trapped electrons
to the valence bond, thus emptying the F centres
• Now the phosphor i.e IP can be used again for radiation exposure
• If used with care, a plate will produce thousands of images(>50000 exposures)
• Plates should be run at least once a week under erase cycle by flooding the cassette with
light.

10. Patient ID station and Digitizer
• Before exposing the casette,the pts
demographic and exam data is stored on
the microchip attached on casette.
• This is done by inserting the cassette in a
slot of ID ststion and entering the data
with the help of keyboard
• After this plate is inserted into the
digitizer where it is scanned with a high
power laser
• Then the digitized image data is
processed on a processing server and is
displayed on monitor.

15. Processing Of Digital Image
• Adjust and optimize the image contrast
• Reduce image noise
• Increase visibility of details

16. Difference betn CR & Conventional
• Less time consuming
• Improved image quality
• Less pt dose
• Images can be stored for long time
• No chemicals required
• High equipment cost
• No need to worry about film
wastage

17. DIGITAL RADIOGRAPHY (DR)
• It is a technique in which conventional silver halide film or PSP screen
is replaced by photo electronic receptor which is connected directly
to computer
• No need of imaging plate (ip) / cassette to be taken to digitizer for
processing of film (like Computed Rdaiography)
• most recent & advanced technology of radiography

18. Principle
• XRAYS
DETECTOR -DDR/IDR
ELECTRONIC SIGNALS
TFT/CCD
DIGITAL SIGNAL
COMPUTER
• X-ray signals can be detected
by
using detectors
• xrays falls on detectors which
convert xray signals into
electronic signals.
• These electronic signals falls
on TFT/CCD where they are
converted into digital signals

19. COMPONENTS
• X-ray equipment
• Detector - Direct/Indirect
• TFT(Thin Film Transistor)/ FPT(flat panel transistor)
• CCD(Chrage Couple Devices)
• Computer System

20. XRAY Equipment- Same xray machine as used in conventional
DETECTOR- Converts Xray signals into electronic signals
1. DDR-Direct Digital Detector
2. IDR-Indirect Digital Detector

21. IDR
• Consists of -- 1]SCintillation crystals,, 2] Photo diode
1. SCINTILLATION Crystals-- (1)cesium iodide OR
(2)Gadolinium oxysulphide
Function- X-Ray signals Light signals
2. PHOTO DIODE--Amorphous Silicon (light sensitive
material)
Function- Light signal Electronic Signals
XRAY PHOTONS
scintillation phosphor
crystals
LIGHT PHOTONS
silicon photodiode
ELECTRONIC SIGNALS

23. DDR
• Amorphous selenium-
Photoconducting material
Function--
Direclty converts
X-RAY signals Electronic
signals

24. TFT(Thin Film Transistor)
• Converts electronic signals
generated by detectors into digital
signals
• Can be used in both DDR & IDR
• Has 3 components
1. Source == Capacitor
2. Gate -- Connected to horizontal
lines (rows)
3. Drain -- Connected to
vertical/read out lines (columns)

25. • TFT is basically an electronic switch that can be made
ON & OFF
-ve voltage applied to gate-- OFF
+ve voltage applied to gate-- ON
• Initially the capacitor (source) that stores the charge is
earthed , so that all the residual charges are passed to
ground -{0 charge}
• During X-ray exposure -ve voltage to gate-- TFT (switch)
is off--
so charge accumulated in each detector element is
stored in capacitor
• During X-ray readout process +ve voltage to gate (one
row at a time)-- TFT (switch) = ON
This will connect vertical wires C1 &C2 to
multiplexor through switches S1 & S2.
Multiplexor amplifies the charge and allows it to
pass to digitizer

26. CCD(Charge Coupled Devices)
• CCD forms images from visible light (unlike TFT - from
electronic signals) hence can be used only with IDR
• it is an integrated circuit (in form of chip) made up of
Metal oxide Crystalline Silicon Capacitor MoCSC
• CCD has individual pixel elements:: when visible light
falls on each pixel - electrons are liberated from pixels
• e- in every pixels are shifted to next pixel
• The bottom row is read out first pixel by pixel and the
charge is shifted to the read out electrons-- which
produces an electronic signal
• This signal is digitized by Analog to Digital Converter
(ADC) & will be used to construct final image matrix

27. COMPUTER SYSTEM
• Here the digital image is manipulated by different means like contrast
enhancement , brightness control etc.
• from here the digital image will go to either printer or storage system

28. WORKING OF DIGITAL RADIOGRAPHY
• By using IDR
XRAY TUBE
Scintillation crystals
light signals
xrays
Si. Photodiode
electronic signals
TFT
Digital signal
Computer
XRAY TUBE
SCINTILLATION CRYSTALS
light signals
CCD
Digital signal
COMPUTER
xrays

29. • BY Using DDR
XRAY TUBE
SELENIUM
electronic signal
TFT
Digital signal
COMPUTER

30. • ADVANTAGES OF DR
1. No chemiccals required for image processing
2. Eliminitaion of dark room
3. Less time consuming
4. Less radiation dose tthe pt
5. Ability to edit the image
6. Better image quality
• DISADVANTAGES OF DR
1. More expensive
2. Skilled workforce needed

31. CR
• Components- cassette- labour
intensive step
• Cassette reading takes time
• Can view images after some
time
• Low initial investment
• Lower image quality
DR
• Component- Detectors- no
labour
• Immediate reading
• Instantly
• Higher
• Higher image quality

32. Detective Quantum Efficiency
• How efficiently a system converts the x-ray input signal into a useful output image.
• • DQE is used to measure the quality of a digital image by looking at the combination of
the effects of noise and contrast on the imaging system.
• • Noise, cannot be avoided in digital imaging.
• The effect of noise is usually expressed as signal-to-noise ratio (SNR). Signal refers to the
useful image information, and noise refers to information that is not useful to image
formation. So, The more signal you have with less noise, the higher the quality of the
image.
• . In other words, high SNR or low system noise allows the capture of the most useful
image information and consequently yields a higher quality image.

33. Detective Quantum Efficiency
• Contrast in digital imaging refers to the system's ability to accurately
reproduce an object's actual contrast.
• ⚫ Digital detectors are able to produce very high-contrast resolution,
which allows for the display of thousands of shades of gray that can
be enhanced with automatic contrast enhancement and various
parameters.
• ⚫ The goal is to achieve high DQE so that there exists the ability to
image small and low-contrast objects.

34. Detective Quantum Efficiency
•DQE Comparison
⚫ Indirect and direct DR capture technology has increased DQE over
CR
⚫ DR direct capture technology has the highest DQE of all systems
because it does not have the light conversion step and consequently no
light spread.

35. DR Spatial Resolution
• Depending on the physical characteristics of the detector, spatial resolution can
vary a great deal.
• • Noise remains constant in any particular system; however, there comes a point
at which the most signal that can be captured has been captured and no more is
available to increase the SNR.
• . As pixel size decreases, the amount of signal captured decreases so that the
finer a matrix is, the lower the SNR will be at each pixel. It should be clear, then,
that there is a balance between pixel size and noise that manufacturers have to
work toward in order to achieve the best spatial resolution possible
• • Excessive image processing, in an effort to alter image sharpness, can lead to
excessive noise.

36. THANK YOU