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Computed radiography and digital radiography- CR/DR

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Ashim Budhathoki

This document provides an overview of computed radiography (CR). It discusses the history and components of CR, including imaging plates, digitizers, and printers. The working mechanism is explained, from image acquisition using an imaging plate exposed to X-rays, to laser scanning to release photons detected by a photomultiplier tube and digitized to form the image. Advantages include comparable image quality to film and ability to process images digitally. The document also compares CR to conventional X-ray and digital radiography.

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COPUTED RADIOGRAPHY
INTRODUCTION The term computed radiography (CR) refers to the process of creating a diagnostic digital image from data acquired with an imaging plate (IP) and reader. The CR process includes image acquisition, processing, and display. Was the first digital technique available commercially. The most common technique for producing digital image. Primary reason for being the most common technique is that it is cheapest. Commercial CR has been widely used in human medicine during the past decade. Equine practitioners led the way, taking advantage of mobile and portable systems with the ability to acquire and view diagnostic radiographic images in the field.
CR UNIT PORTABLE MACHINE
H ISTORY Present day computed radiography (CR) is based on the use of photostimulable phosphors, which are also known as storage phosphors (Sonoda et al 1983). They are commercially the most successful detectors for digital radiography. The phosphors used are most often in the barium fluorohalide family (Barnes 1993) in powder form and deposited onto a substrate to form an imaging plate or screen. In CR, an imaging plate (IP) containing the storage phosphor is positioned in a light-tight enclosure, exposed to the x-ray image and then read out by raster scanning with a laser to release the PSL. The blue PSL light is collected with a light guide and detected with a photomultiplier tube (PMT). The PMT signal is digitized to form the image on a point-by-point basis (Fujita et al 1989).
COMPONENTS For acquisition, processing, and displaying the digital image CR system needs different components : 1. Normal x-ray unit 2. CR plate 3. Digitizer/ scanner 4. Printer-for hard copy output. 5. PMT and AD converter.
COMPONENTS OF COMPUTED Psp plate X-ray unit Printer Digitizer
Psp plate Refers to photo stimuable phosphor plate. Also known as CR plate. A CR plate is based on a fluorescent screen and housed in a conventional cassette. Most CR systems use a Barium Fluoro-bromide phosphor, This is then doped with Europium. The Europium changes the chemical structure of the phosphor to trap electrons on x-ray exposure. During and after exposure, about 50% of the electrons remain trapped, the rest fall back almost immediately Over time, due to thermal energy, trapped electrons fall back spontaneously over many hours The time limitation for a x-ray image receptor keep without reading in digitizer is about 8 hours.
WORKING MECHANISM PMT PSP PLATE e- AD converter computer CR image
WORKING MECHANISM PSL (photo stimuable luminance) When the PSP plate is irradiated the electron of the phosphor material within PSP plate are excited which are equally distributed on the PSP plate and get trapped at higher energy level. If we introduce laser beam to the plate then such trapped electron tends to fall back to their original state from higher energy level, during this process the light Is immited which is equivalent to band energy of trapped electron. This phenomenon is called PSL .
WORKING MECHANISM Such immited light is detected by PMTs(photo multiplier tube) which converts the light photons into electrons. Those electron combine to form analog signal which computer cant detect. So, these analog signals are converted to digital signal by AD converter which next pass to the computer for further processing.
WORKING MECHANISM Then computer process the digital signal and creates the digital image and displays in the monitor. Those image can be further processed manipulated and can be transported to other digital devices for clinical evaluation by using PACS and DICOMS. PACS-picture archiving communication system. DICOM-digital imaging and communication system.
WORKING MECHANISM Again such image can be printed as a hard copy if required. Finally the PSP plate is exposed to white beam of light which activates and erase the previous data . So that, this plate can be again used for the next patient.
Computed radiography and digital radiography- CR/DR
ADVANTAGE OF CR Image quality comparable with to conventional screen -film systems Wide dynamic range - ability to image structures of different attenuation values (thorax and abd) Reduction of repeat exposures CR is compatible/upgrade with most conventional x -ray systems Increased savings: no film, chemicals, dark room and storage room required Computer processing of raw image: brightness, contrast, sharpness enhancement, zooming, measurements CR is more tolerant of under / over exposure (wide latitude ) Ability to extract information not possible on conventional radiographs (e.g edge enhancement, masking, cropping) Faster image acquisition DICOM -Digital imaging communications in medicine PACS - Images retrieved from computer archive Teleradiology:- the transmission of radiological patient images, from one location to another for the purposes of sharing studies with other radiologists and physicians.
COMPARISION BETWEEN COVENTIONAL X-RAY AND CR CONVENTIONAL X-RAY COMPUTED RADIOGRAPHY Older technology. Advanced technology Cheaper technology. Expensive technology. Post processing by using various chemicals. Post processing by using signals. Intensifying screen is used. Intensifying screen is not used. Manipulation of image is not possible once it is formed. Manipulation of image is possible once it is formed. Trained manpower can also function it. Skilled manpower is required. Film is used as IR. PSP plate is used as IR. Formed image cant be erased. Formed image can be erased and reused for next patient.
DIGITAL
INTRODUCTION DR refers to Direct Digital Radiography . Digital radiography is a form of X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. DR uses detector panel as image receptor. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also, less radiation can be used to produce an image of similar contrast to conventional radiography. High image quality comparison to CR and conventional x-ray film.
Components of DR The components of DR includes: 1. Detector 2. Charge coupling device(CCD) 3. Photo cell 4. PMT 5. AD converter
DETECTAR There are two types of detectors:- 1. Gas filled detector. 2. Solid state detector.
Construction of gas filled detector Cylindrical in shape. Filled with gas ie.xenon gas in known amount and internally coated with Graphite. Centrally an electrode is placed which connects the galvanometer and cylindrical tube. It consists of battery with certain potential where negative terminal of battery is connected to cylindrical shape and positive terminal of battery is connected to electrode.
WORKING MECHANISM OF GFD When the x-ray interacts with gas within the detector the x-ray ionize the gas through which it travels. As the electrode is positively charged , it attracts the negatively charge and the electron flow through the electrode. This movement of electron causes the movement of meter within ammeter which indicates the radiation dose.
SOLID STATE DETECTAR CONSTRUC-TION PMT AD CONVERT ER CC P Cesium iodide e- e- e- e- e- e- Digital signal Analog signal X- rays
WORKING MECHANISM OF SSD As soon as the x-ray interacts with phosphor material the light get emitted The produced light photons are directed towards PMT. Coupling device is used to avoid the missing of light photons. These light photons are converted into the electrons by the multiplication by PMT , those electrons combine to form analog signal.
WORKING MECHANISM OF SSD These analog signals are converted to digital signal by AD converter which next passed to computer for further processing to create DR Image. The image can be further processed manipulated and can be transferred to other digital device for clinical evaluation by using PACS and DICOMS. Such image also can be printed as hard copy whenever required.
COMPARISION BETWEEN CR AND DR COMPUTED RADIOGRAPHY DIGITAL RADIOGRAPHY Filmless technology. Casstteless technology. Works slower. Works faster. Lesser image quality. Higher image quality. High radiation dose Less radiation dose Lesser life span. higher life span. Simple to used. Hectic mortality Less costly. Costly. Less qualified personal can also function it. Well qualified personal is required.

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Computed radiography and digital radiography- CR/DR

  • 3. INTRODUCTION The term computed radiography (CR) refers to the process of creating a diagnostic digital image from data acquired with an imaging plate (IP) and reader. The CR process includes image acquisition, processing, and display. Was the first digital technique available commercially. The most common technique for producing digital image. Primary reason for being the most common technique is that it is cheapest. Commercial CR has been widely used in human medicine during the past decade. Equine practitioners led the way, taking advantage of mobile and portable systems with the ability to acquire and view diagnostic radiographic images in the field.
  • 5. H ISTORY Present day computed radiography (CR) is based on the use of photostimulable phosphors, which are also known as storage phosphors (Sonoda et al 1983). They are commercially the most successful detectors for digital radiography. The phosphors used are most often in the barium fluorohalide family (Barnes 1993) in powder form and deposited onto a substrate to form an imaging plate or screen. In CR, an imaging plate (IP) containing the storage phosphor is positioned in a light-tight enclosure, exposed to the x-ray image and then read out by raster scanning with a laser to release the PSL. The blue PSL light is collected with a light guide and detected with a photomultiplier tube (PMT). The PMT signal is digitized to form the image on a point-by-point basis (Fujita et al 1989).
  • 6. COMPONENTS For acquisition, processing, and displaying the digital image CR system needs different components : 1. Normal x-ray unit 2. CR plate 3. Digitizer/ scanner 4. Printer-for hard copy output. 5. PMT and AD converter.
  • 7. COMPONENTS OF COMPUTED Psp plate X-ray unit Printer Digitizer
  • 8. Psp plate Refers to photo stimuable phosphor plate. Also known as CR plate. A CR plate is based on a fluorescent screen and housed in a conventional cassette. Most CR systems use a Barium Fluoro-bromide phosphor, This is then doped with Europium. The Europium changes the chemical structure of the phosphor to trap electrons on x-ray exposure. During and after exposure, about 50% of the electrons remain trapped, the rest fall back almost immediately Over time, due to thermal energy, trapped electrons fall back spontaneously over many hours The time limitation for a x-ray image receptor keep without reading in digitizer is about 8 hours.
  • 10. WORKING MECHANISM PSL (photo stimuable luminance) When the PSP plate is irradiated the electron of the phosphor material within PSP plate are excited which are equally distributed on the PSP plate and get trapped at higher energy level. If we introduce laser beam to the plate then such trapped electron tends to fall back to their original state from higher energy level, during this process the light Is immited which is equivalent to band energy of trapped electron. This phenomenon is called PSL .
  • 11. WORKING MECHANISM Such immited light is detected by PMTs(photo multiplier tube) which converts the light photons into electrons. Those electron combine to form analog signal which computer cant detect. So, these analog signals are converted to digital signal by AD converter which next pass to the computer for further processing.
  • 12. WORKING MECHANISM Then computer process the digital signal and creates the digital image and displays in the monitor. Those image can be further processed manipulated and can be transported to other digital devices for clinical evaluation by using PACS and DICOMS. PACS-picture archiving communication system. DICOM-digital imaging and communication system.
  • 13. WORKING MECHANISM Again such image can be printed as a hard copy if required. Finally the PSP plate is exposed to white beam of light which activates and erase the previous data . So that, this plate can be again used for the next patient.
  • 15. ADVANTAGE OF CR Image quality comparable with to conventional screen -film systems Wide dynamic range - ability to image structures of different attenuation values (thorax and abd) Reduction of repeat exposures CR is compatible/upgrade with most conventional x -ray systems Increased savings: no film, chemicals, dark room and storage room required Computer processing of raw image: brightness, contrast, sharpness enhancement, zooming, measurements CR is more tolerant of under / over exposure (wide latitude ) Ability to extract information not possible on conventional radiographs (e.g edge enhancement, masking, cropping) Faster image acquisition DICOM -Digital imaging communications in medicine PACS - Images retrieved from computer archive Teleradiology:- the transmission of radiological patient images, from one location to another for the purposes of sharing studies with other radiologists and physicians.
  • 16. COMPARISION BETWEEN COVENTIONAL X-RAY AND CR CONVENTIONAL X-RAY COMPUTED RADIOGRAPHY Older technology. Advanced technology Cheaper technology. Expensive technology. Post processing by using various chemicals. Post processing by using signals. Intensifying screen is used. Intensifying screen is not used. Manipulation of image is not possible once it is formed. Manipulation of image is possible once it is formed. Trained manpower can also function it. Skilled manpower is required. Film is used as IR. PSP plate is used as IR. Formed image cant be erased. Formed image can be erased and reused for next patient.
  • 18. INTRODUCTION DR refers to Direct Digital Radiography . Digital radiography is a form of X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. DR uses detector panel as image receptor. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also, less radiation can be used to produce an image of similar contrast to conventional radiography. High image quality comparison to CR and conventional x-ray film.
  • 19. Components of DR The components of DR includes: 1. Detector 2. Charge coupling device(CCD) 3. Photo cell 4. PMT 5. AD converter
  • 20. DETECTAR There are two types of detectors:- 1. Gas filled detector. 2. Solid state detector.
  • 21. Construction of gas filled detector Cylindrical in shape. Filled with gas ie.xenon gas in known amount and internally coated with Graphite. Centrally an electrode is placed which connects the galvanometer and cylindrical tube. It consists of battery with certain potential where negative terminal of battery is connected to cylindrical shape and positive terminal of battery is connected to electrode.
  • 22. WORKING MECHANISM OF GFD When the x-ray interacts with gas within the detector the x-ray ionize the gas through which it travels. As the electrode is positively charged , it attracts the negatively charge and the electron flow through the electrode. This movement of electron causes the movement of meter within ammeter which indicates the radiation dose.
  • 23. SOLID STATE DETECTAR CONSTRUC-TION PMT AD CONVERT ER CC P Cesium iodide e- e- e- e- e- e- Digital signal Analog signal X- rays
  • 24. WORKING MECHANISM OF SSD As soon as the x-ray interacts with phosphor material the light get emitted The produced light photons are directed towards PMT. Coupling device is used to avoid the missing of light photons. These light photons are converted into the electrons by the multiplication by PMT , those electrons combine to form analog signal.
  • 25. WORKING MECHANISM OF SSD These analog signals are converted to digital signal by AD converter which next passed to computer for further processing to create DR Image. The image can be further processed manipulated and can be transferred to other digital device for clinical evaluation by using PACS and DICOMS. Such image also can be printed as hard copy whenever required.
  • 26. COMPARISION BETWEEN CR AND DR COMPUTED RADIOGRAPHY DIGITAL RADIOGRAPHY Filmless technology. Casstteless technology. Works slower. Works faster. Lesser image quality. Higher image quality. High radiation dose Less radiation dose Lesser life span. higher life span. Simple to used. Hectic mortality Less costly. Costly. Less qualified personal can also function it. Well qualified personal is required.