CR & DR..(5).pptx

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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. C ASSETTE Light weight p l a s t i c b a c k e d b y 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 Protective layer -plastic made-protects phosphor layer phosphor layer -photostimulable phosphor that traps electrons during exposure Anti halo and reflective layer -reflects light to reader Conductive layer -absorbs light as well as any electrical charge 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 PHOTO-STIMULABLE LUMINESCENCE 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. PRINCIPLE contd. 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) P l a t e s s h o u l d b e r u n a t l east o nce a week u n d er e r a s e c y cle b y f l o o d ing t h e c a s s e tte w ith l i g h t .

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.

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

12. 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

13. 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

14. 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

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

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

17. IDR Consists of -- 1]SCintillation crystals,, 2] Photo diode 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

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

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

20. 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

21. 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

22. 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

23. 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

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

25. ADVANTAGES OF DR No chemiccals required for image processing Eliminitaion of dark room Less time consuming Less radiation dose tthe pt Ability to edit the image Better image quality DISADVANTAGES OF DR More expensive Skilled workforce needed

26. 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

27. D e t e c t i v e Q u a n t u m E f f i c i e n c y • 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. S o , 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.

28. 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 v a r i o u s parameters. ⚫ The goal is to achieve high DQE so that there exists the ability to image small a n d l ow-contrast objects.

29. 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.

30. 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 a c hieve the best spatial resolution possible • Excessive image processing, in an effort to alter image sharpness, can lead to excessive noise.

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