DIGITAL RADIOGRAPHY-SABBU KHATOON .pptx

Presentation on Digital Radiography.

1. DIGITAL RADIOGRAPHY Presented by:- Sabbu Khatoon Roll No:- 156 BSc. MIT 2 nd Year MMC,IOM

2. Presentation Layout Introduction & History of Digital Radiography Terminologies related to DR Principle & Types of DR Computed Radiography Scanned Projection Radiography Direct Digital Radiography Direct & Indirect DDR Advancements in CR & DR Detectors used in TUTH

3. Conventional Radiography Uses film and IS in its image formation process. X-rays pass through the patient and expose the film, creating latent image. Involves chemical processing to reveal the image on X-ray film. It had limited manipulation options after film processing.

4. Introduction to Digital Radiography Filmless imaging system Digital X-ray sensors are used instead of traditional photographic films. Concept given by Albert Jutras [ 1950,Canada] during his experimentation with teleradiology. First DR application is the invention of CT in 1967 by Godfrey Hounsfield

5. History of Digital Radiography YEAR TECHNIQUE Introduction of DSA DSA first put into clinical use 1980 Use of storage phosphor image plates Amorphous selenium based image plates 1990 Charged couple device slot-scan DR was introduced Selenium drum DR Amorphous silicon CSI flat panel detector 1997 Gd based FPD Gd based portable FPD 2001 Dynamic FPD fluoroscopy DSA 2007 Portable CR system

6. Terminologies related to DR Pixel: short for “picture element”. Small, discrete units of digital information that together constitute an image. Resolution: level of clarity or detail in an image. Gray Scale: refers to total no. of shades of gray visible in an image Voxel: Volume element. A 3-Dimensional element that includes depth. A pixel is essentially the end of the voxel.

7. Components of Digital Imaging Capture element : Component in which the X- ray is captured. In CR, it is PSP & in DR it may be CsI, Gd-OS or a-Se. Coupling element: It transfers x-ray generated signal to the collection element. It may be a lens or fiber optic assembly, a contact layer or a-Se. Collection element: may be a photodiode, CCD or TFT. The photodiode & CCD are light-sensitive whereas TFT is charge sensitive.

8. PRINCIPLE Of DR The digital detector is exposed to X-rays generated by a standard tube. The energy absorbed by the detector is transformed into electrical charges, which are then recorded, digitized and quantified into a gray scale. After sampling, post-processing software is required for organizing the raw data into a clinically meaningful image.

9. Types of Digital Radiography FIG:- An organizational scheme for digital radiography

10. Computed Radiography (CR) Records radiographic images on photostimulable phosphor plates instead of film/screen image receptors and the image is acquired in digital Form. Based on the principle of Photo- stimulable Luminescence. The commonly used phosphor is barium fluorohalides: BaFBr (85%) and BaFI (15%):with Eu (europium).

11. CONTD.. The PSP plates are placed inside a special cassette for exposure. During exposure , x-ray energy is absorbed temporarily in the PSP crystal by bringing electrons to higher energy levels. Cassette is placed in a reader(Digitizer) to capture and analyze the image data. Uses a computer workstation and viewing station and a printer. CONSISTS OF :- 1. CASSETTE 2. IMAGING PLATE 3. READER

12. CR: Cassette Looks like conventional radiography cassette. Consists of durable, lightweight plastic material. Consists of 150 µ lead for backscatter protection. Instead of IS, there is antistatic material that protects against static electricity build up, dust collection and mechanical damage to plate.

13. Fig:-CR cassette with Imaging Plate(IP) Fig:-Conventional Cassette with Screen-Film

14. CR: Imaging Plate (IP) First introduced by Fuji, Japan, in 1983 and is similar to that of a screen-film cassette. Responsible for capturing the X-ray image. They are made up of Photostimulable phosphor(PSP). PSPs, barium flurohalide, is fashioned similarly to a radiographic IS. Since latent image occurs in form of metastable electrons, such screens are called Storage phosphor screen (SPSs). IP

15. Layers of IP PROTECTIVE LAYER : a very thin, tough, clear plastic that protects the phosphor layer. PHOSPHOR LAYER: consists of photostimulable phosphor that traps electrons during exposure. Usually made up of BARIUM FLUROHALIDE family. Light REFLECTIVE LAYER: It sends light in a forward direction when released in the cassette reader. Maybe black to reduce the spread of stimulating light and escape of emitted light. Conductive layer : This layer grounds the plate to reduce static electricity problems and to absorb light to increase sharpness .

16. SUPPORT LAYER : Semirigid layer that provides strength . LIGHT SHEILDING LAYER BACKING LAYER Soft polymer that protects back of cassette. BAR CODE LABEL : Used in matching and identification FIG:- A showing the Imaging plate, B showing it’s construction

17. What happens in the IP? When x ray is exposed, x-ray energy is absorbed by BaFBr phosphor. Absorbed energy causes the divalent Europium atoms to be oxidized and changed into trivalent state. The exited e-s becomes mobile & interact with F-center The F-center traps these e-s in a higher energy meta-stable state in the form of latent image. During this process , about 50% of the e-s returns to the ground state immediately However , the remaining meta-stable e-s also returns to the ground state over time. This causes the latent image to fade and the IP must be read soon after exposure.

18. CR: Reader The CR reader represent the mechanical, optical and computer modules.

19. CR: Reader (Mechanical features) When the CR cassette is inserted into the CR reader , the IP is removed & is fitted to a precision drive mechanism. The drive mechanism moves the IP slowly along the long axis of the IP, known as slow scan mode . A deflection device deflects the laser beam back & forth across the IP which is called fast scan mode.

20. CR: Reader (Optical features) It precisely interrogate each meta-stable e-s of the latent image in the precise fashion. Its components include the laser, beam-shaping optics, light-collecting optics, optical filters & a photodetector. The He-Ne gas laser is the source of stimulating light which is monochromatic. The gas laser has been largely replaced by the solid state laser which produces the light of longer wavelength which are less likely to interfere with emitted light.

21. The light beam is focused into the reflector by a lens system that keeps the beam diameter small (less than 100micrometer). Smaller the laser beam size , higher the spatial resolution of the image. Emitted light is focused by fiber optic collection assembly & is directed at the photodetector, PMT, or CCD. Before photo-detection , the light is filtered so that none of the long-wavelength stimulation light reaches the photo-detector. Filtering improves SNR.

22. CR: Reader (Computer control) The output of the photodetector is a time varying analog signal that is transmitted to a computer system. This shapes the signal before the final image is formed. Then, the analog signal is digitized with the help ADC The computer of the CR reader is in control of the slow scan & the fast scan.

23. CR: Reader WORKING:- The IP is mechanically removed from the cassette when it moved into the reader. The IP is translated across the readout stage in the vertical direction (y-direction) & the scanning laser beam interrogates the plate horizontally (x-direction). As the red laser light strikes the IP at the location (x , y) , the trapped energy is released from it in the form of light which is of different colors than stimulating laser light. A fraction of emitted light travels through the fiber-optic light guide & reaches the PMT

24. CR: Reader WORKING:- The electronic signal that is produced by PMT is digitized & stored in the memory. Therefore for every location (x , y) , a corresponding gray scale value is determined & thus digital image is produced. The plate is then exposed to bright white light to erase any residual trapped energy and returned to the cassette for reuse. This whole process takes typically about 30-90 seconds in most of the systems.

25. Advantages of CR Faster image receptor , so lower patient dose is possible. High image quality compared to conventional film screen system Post- processing , manipulation & storage of images. Repeat examinations are reduced due to wide exposure latitude. IP is reusable , no need to reload the cassette. Compatible with most conventional x ray unit and therefore be introduced without the need to replace existing equipment

26. Disadvantages of CR High equipment cost. Long time to view image. Spatial resolution is usually lower than that with conventional screen film radiography.

27. Scanned Projection Radiography Developed by CT vendors to facilitate patient positioning after the introduction of 3rd gen CT scanners. Basically, dedicated for chest DR. WORKING :- The method consists of placing the x-ray tube and detector assembly in such a position that the patient may be moved linearly through the x-ray beam As it is moved, data are collected by the computer from the detector array, and the image of the patient is thus stored in computer memory for subsequent manipulation and display. Fig:- A scanned projection radiograph obtained in computed tomography by maintain the energized X-ray tube- detector array fixed while the patient is translated through the gantry

28. This system is based on the well collimated narrow fan beam corresponds to the detector array. SPR uses the CT- gantry & computer to produce an image that looks like conventional radiography. ADVANTAGES - High image contrast - Wide dynamic range - Post processing DISADVANTAGES -Exposure time is long -Poor spatial resolution -Radiation dose is more Fig:- A scanned projection radiograph of the Entire trunk of the body obtained in computed tomography

29. Direct Digital Radiography Direct digital radiography, a term used to describe total electronic image capturing. Eliminates the need for an image plate altogether. It’s of two types:- DIRECT CONVERSION TYPE:- Photoconductors like amorphous selenium directly convert X-rays into electrical charges. Flat panel based INDIRECT CONVERSION TYPE:- It involves two steps- - X-ray to visible light conversion by scintillator - Visible light to charges by photo detectors - CCD/CMOS based, Flat panel

30. CONTD.. Scintillator :- material that exhibits scintillation , the property of luminescence, when excited by ionizing radiation. Types :- Unstructured scintillator : With use of unstructured scintillator, the visible light emitted by the material can spread to adjacent pixels, thereby reducing spatial resolution. Structured scintillators: To reduce the problem of scatter, some manufacturers now use a structured scintillator that consists of cesium iodide crystals that are grown on the detector

31. CONTD.. Thallium-doped cesium iodide (CsI) is the most commonly used phosphor material. Another material that is used is gadolinium oxysulphide or Gadox (Gd2 O2S). CsI - based detectors are more efficient in X-ray absorption than gadox detectors and have better DQE

32. DIRECT DR VS INDIRECT DR

33. Photomultiplier Tube Type of photo- detectors and are highly light - sensitive device especially whose wavelength lies in range of UV, Visible & IR region of Electromagnetic Spectrum. These detectors amplify the current produced by incident photon by as much as 100 million times , through series of dynodes when the incident flux of light is very low. Their operation depends on two processes:- - Photoelectric effect - Secondary Emission

34. PMT A photomultiplier consists of five main parts : A cathode which is coated with a material of low work function An anode to collect electrons A series of dynodes between the cathode and the anode An external power supply which produces an electric field between the cathode and first dynode, between the dynodes, and between the last dynode and the anode. An external current meter to measure the number of electrons collected at the anode, and a recorder to collect the information.

35. PMT

36. Photodiode Semiconductor light sensors for photodetection Generates current/voltage when P-N junction is illuminated Used in radiography to convert visible light from scintillators into electrical signals There are various types of photodiode - PIN photodiode - P-N photodiode - Avalanche photodiode Fig:- PIN Photodiode

37. Charged Coupled Device Uses photosensitive silicon chips Converts light into digital signals Integrated circuit made of amorphous silicon Illuminated silicon layer generates electrical charge Charge accumulates in pixel cells Readout occurs in pixel by pixel manner A tiled CCD designed for digital radiographic imaging

38. Working of CCD CCD consists of array of light- sensitive pixels. Pixels are organized in rows and columns Each pixel converts photons to electrical charge via the photoelectric effect. The number of electrons released depends on the intensity of light. These electrons are build up in the pixel. The electrons are kept in the pixel by electronic barriers on each side of the pixel Once the CCD chip has been exposed, the electronic charge that resides in each pixel is read out.

39. Charge is readout in “bucket brigade” fashion ,i.e.; The electronic charge is shifted pixel by pixel by appropriate control of voltage level at the boundaries of each pixel. Thus ,the charge pocket in one column moves in unison & finally reaches the pixel in the bottom row. The bottom row is read out pixel by pixel & the charge is shifted to the read out electronics, which produces an electronic signal. This signal is digitized by a ADC and the digital signal is used to construct image matrix. This process is repeated until all the pixels in the detector are read out completely. CONTD.. Fig:- Movement of charge pockets column by column through bottom row

40. Advantages of CCD The main advantage of the CCD is the extremely fast discharge time which is useful in cardiac catheterization where high-speed imaging is critical to visualizing blood flow. Sensitivity- ability to detect & respond to very low levels of visible light. Hence reduces the patient dose. Dynamic range- ability to respond wide range of light intensity. Radiation response of CCD is linear. Size - its size is very small that makes it highly adaptable to DR in its various forms. It measures 1 to 2 cm. Fig:- Radiation response of CCD Compared with that of a 400- speed Screen-film IR

41. Disadvantages of CCD The principal disadvantage of CCDs is that they are physically small and consequently can image only a small region. When large FOV is needed to image, it is impossible to image the light into the surface of CCD chip without losing the light photons. The assembly of multiple CCD(mosaic CCD) is used to overcome this problem.

42. CMOS Recent Advancement is focusing on Complimentary-Metal-Oxide Semiconductors(CMOS) technology and are being used instead of CCD These are newer design of Transistors. CMOS is a type of MOSFET(Metal-Oxide-Semiconductor Field- Effect Transistor) and utilizes it as individual pixel elements. CMOS sensors consists of array of pixels that converts X-rays into electrical signals.

43. Advantages of CMOS over CCD Cheaper compared to that of CCD (i.e. the CMOS chip incorporates amplifiers and A/D-converters, which lowers the cost since it contains all the logics needed to produce an image) Consumes little power (CCD uses 100 times more power than CMOS) CMOS Detectors are more flexible, more stable, more sensitive, and faster than TFT-based flat panel detectors while producing higher resolution images . Faster readout speed Clinical benefits in medical applications include lower radiation dose to the patient without compromising image quality.

44. Disadvantages of CMOS Lower light sensitivity compared to that of CCD More susceptible to noise

45. FLAT PANEL DETECTORS Comprises numerous detector elements storing charge in response to x-ray exposure. Charge buildup in each element held by capacitors during exposure. Post-exposure, electronics read out the charge in each detector element. Each detector element has a transistor, utilizing thin-film deposition tech. Referred to as thin- film transistor (TFT) image receptors due to transistor use. It may be of Direct or Indirect in nature which categorize the DR into Direct DR and Indirect DR. Fig:- A flat panel detector array comprises of large no. of detector element. Each contains both a light sensitive area and a region that holds electronic components

46. Fig:- Indirect detection in flat panel system Fig:- Direct detection in flat panel system

47. CESIUM IODIDE/ AMORPHOUS SILICON Earlier, CsI was used to capture x-ray as well as transmission of resulting scintillation light to collection element. Previously silicon as semiconductor was grown as crystal. Later, amorphous silicon was identified and can be painted on supporting surface. So, collection element is silicon sandwiched as a TFT. Is an indirect DR process. Fig:- CsI phosphor in digital radiography IR is available in form of filaments to Improve x-ray absorption and reduce light dispersion

48. CESIUM IODIDE/ AMORPHOUS SILICON IR is fabricated into individual pixels. Each pixel has a light sensitive face of a-Si with a capacitor and a TFT embedded. Geometry of pixel is imp. As portion of pixel face is occupied by conductors, capacitors and TFT, it is not totally sensitive to incident image forming x-rays.

49. FILL FACTOR Percentage of the pixel that is sensitive to x-rays is Fill factor. Spatial resolution in DR is pixel limited. As pixel size is reduced, spatial resolution improves but at the expense of pt. radiation dose. With smaller pixel size, fill factor is reduced and x-ray intensity must be increased to maintain adequate signal strength. Nowadays, nanotechnology promises increased fill factor and improved spatial resolution at even lower pt. dose.

50. GdOS/ a-Si Widely used as capture element of most rare earth Intensifying Screens. Same as CsI/a-Si image receptor. Thickness of GdOS determines speed of IR. Increasing the thickness of GdOS in DR IR increases the speed of the system with no compromise in spatial resolution.

51. AMORPHOUS SELENIUM No scintillation phosphor is required. A-Se is both capture element and coupling element. Image forming x-rays beam interacts directly with a-Se, producing charge pair. Approx. 200 micrometer thick and sandwiched between charged electrodes. A-Se create electron hole pairs through direct ionization of selenium. Created charge is collected by storage capacitor and remains there until the signal is read by switching action of TFT. Fig: Use of a- selenium as an IR capture element eliminated the need for a scintillation phosphor

52. INDIRECT CONVERSION Indirect conversion with CCD X-ray energy is converted into light by a scintillator such as Tl doped cesium iodide. The amount of light emitted is then recorded by the CCD, and the light is converted into electrical charges. It is an array consisting of several CCD chips which forms a detector area similar to that of a flat-panel detector. CCDs can be used for radiography as part of either a lens-coupled CCD system or a slot-scan CCD system. CCD-based systems were comparable to flat-panel detectors in terms of image quality and allowed slightly superior low-contrast visualization. CCD can be tiled to receive the light from an area x-ray beam as it interacts with a scintillation phosphor such as CsI

53. INDIRECT CONVERSION Indirect Conversion with a Flat-Panel Detector Indirect conversion DR systems are “sandwich” constructions consisting of a scintillator layer , an amorphous silicon photodiode circuitry layer, and a TFT array. X-ray photons reach the scintillator, visible light proportional to the incident energy is emitted. It is recorded by an array of photodiodes and converted to electrical charges. These charges are then read out by a TFT array. Scintillators usually consist of CsI or GdOS .The advantage of CsI-based scintillators is that the crystals can be shaped in thin needles, which can be arranged perpendicular to the surface of the detector.

54. DIRECT CONVERSION Direct conversion requires a photoconductor that converts x-ray photons into electrical charges by setting electrons free . Typical photoconductor materials include amorphous selenium, lead iodide, lead oxide, thallium bromide, and gadolinium compounds. The most commonly used element is selenium. Selenium-based direct conversion DR systems are equipped with either a selenium drum or a flat-panel detector. A-Se is both capture & coupling element. Selenium is a photoconductor that when exposed to radiation alters its electrical conductivity proportional to the intensity of radiation Fig:- Use of a-selenium as an IR capture element eliminated the need for a scintillation phosphor

55. DIRECT DR vs INDIRECT DR

56. Sequence of activity for screen-film radiography Transition from s/f radiography to Computed radiography

57. Several additional steps are eliminated when progressing from s/f through CR to DR

58. Comparison between CR and DDR

59. Advantages of DR Digital image capture Environmental friendly : Elimination of costly film processing steps Superior gray-scale resolution : uses 256 colors of gray compared to 16-30 shades on film. Lower radiation dose : 50-80% less radiation with no loss of image quality Can be stored electronically; easier to retrieve patient’s records Image enhancement/manipulation for better interpretation: Contrast, colorization, magnification, sharpness, and image orientation Computer- Aided Diagnosis (CAD) Potential for teleradiology

60. Disadvantages of DR High cost depending on manufacturer and features Technology changes: System may become obsolete and no longer has support Artifacts: occurs during digital image acquisition and /or retrieval process. The spatial resolution of DR image recording systems is lower than that of F/S image recording systems however ;The impact of such a lower spatial resolution system on clinical performance is not significant . Dose-creep : since , exposure latitude is wide , high exposure technique may be used which increases the patient dose which is called dose-creep. This can be reduced by exposure indicator or exposure index which gives the user feedback about the actual dose.

61. Advancements in CR 1. Automated CR systems: It reduces the readout time and by removing the step of cassette handling. The readout time of PSP plate is reduced to less than 10 sec by line scan lasers and photodiode detectors in automated CR systems 2. Newer structured phosphor for PSP plates: Newer phosphors like cesium bromide having a structured needle-shaped configuration of crystals have been recently introduced which reduce light diffusion. They are also more efficient with an increased DQE

62. 3.Mobile CR systems: To save labor, time and improve workflow of critically ill patients requiring bedside X-rays, portable, compact CR systems have been introduced in 2007. Mobile x-ray unit with integrated CR reader eliminates cassette transport. Image available in less than 25 seconds.

63. Advancements in DR Tomosynthesis: In this technique multiple low dose exposures are given from various angles while the X-ray tube moves in an arc and the detector remains stationary. The images can be viewed singly or in a wire loop 2. Dual energy imaging: Dual energy radiography methods are used to generate separate images of bone and soft tissue structures from two exposures made using different radiographic techniques

64. 3. Computer aided diagnosis (CAD): They are important in early detection of cancer of the lung and breast. The suspicious areas are marked by the software for review by the radiologist. The main advantage of CAD is that it alerts the radiologist to avoid overlooking diagnostically significant findings 4. Automatic image stitching: This feature is useful when precise measurements in lengthy anatomical regions like the spine or lower limb are required. 5. Mobile DR: It consists of a 14 × 17 inch flat panel detector connected by a cable to a mobile X-ray system having a monitor. FIG:- Mobile DR

65. 6. Wireless FPDs: A wireless portable DR system can transfer image data wirelessly to the DR system. It does not have any cables and does not interfere with surrounding machines 7. Fluoroscopy and radiography: Real time digital imaging facilitates high quality radiography and fluoroscopy with up to 30 images/sec

66. TUTH Department Detectors 1. Musica Technology DR 14e Agfa @Room no . C2 2. iRay Technology DR panel MARS 1417V @Room no. C3 3. Konika Minolta AeroDR NS 1417(P-41) @Room no. C4

67. Musica Technology Agfa DR panel specifications Rated Voltage 100 – 240 V Detector Type Amorphous Silicon with TFT Pixel Pitch 150 μ m Active Pixel Matrix 2336 x 2836 pixels Conversion screen Csl (Cesium Iodide) and GOS (Gadolinium oxysulphide) Active Area Size 430 mm x 350 mm Effective Pixel Matrix 2336 x 2836 pxl Grayscale 16 Bit Spatial Resolution Min. 3.36 lp /mm Energy Range Standard 40 – 150 kVp

68. iRay Technology DR panel specifications Brand iRay Technology Model MARS 1417V Detector Technology Amorphous Silicon Scintillator Csl Active Area (inch) 14x17 Pixel Matrix 2304x2800 Pixel Pitch ( μ m) 150 Limiting Resolution ( lp /mm) 3.4 AD Conversion (bit) 16 Battery Autonomy (h) 8 WIFI 2.4G and 5G IEEE802. 11 a/b/g/n/ac Trigger Mode ADE (optional) / Software

69. Konica Minolta DR panel specification Product name (model name) AeroDR NS 1417(P-41) Detection Method Indirect conversion Method Scintillator Csl ( Cesium Iodide) External Dimension 384x460x15xmm (15.1x18.1x0.6 inch) Weight (including Battery) 3.6 kg (7.9lb) Pixel Size 150 μ m Image area size 345.6x420.0mm (13.6x16.5 inch) AD conversion 16 bit (65,536 gradients) Usable grid frequency 40lp/cm Durability Print load : 100kg@ Φ 40mm Face load : 150kg @effective image area overall Image storage 200 image Battery Lithium Ion

70. Canon CXDI-701G Wireless DR panel specification Method Scintillator & Amorphous Silicon (a-Si) Sensor LANMIT (Large Area New-MIS sensor and TFT) Scintillator Terbium-doped Gadolinium oxysulphide (Gd2O2S:Tb) Grid Recommended: 52 lp /cm Pixel Pitch 125 x 125 μ m Total Pixel Count 2,800 x 3,408 pixels (Approx. 9.5 Million) Exposure Range Automatic Range Detection (Max. 35 x 42.6 cm) Grayscale 65,536 Steps (16-bit) Voltage AC 100V (50/60 Hz) On board image storage 99 Images Load Tolerance 100 kg @ φ 40 mm, 150 kg @ Entire Area Power Consumption 90 VA Max. (Wireless) / 41 VA Max. ( Wired )

71. Summary Digital radiography is film-less imaging system; digital sensors are used instead of traditional photographic films. The earliest DR was a spin-off from CT & involved a collimated fan x-ray beam. Currently, four methods are used to produce a digital projection radiograph. CR is based on the principle of Photo- stimulable Luminescence; PSP plates instead of film/screen image receptors and the image is acquired in digital Form. CsI scintillation phosphor can be used as capture element for image forming x-rays whose signal is channeled to a CCD through fiber optic channels. CsI scintillator allows greater detection of x-rays, as there is no light spread, & much greater resolution. Amorphous selenium is used as a capture element for x-rays in an alternate DR method.

72. Reference Radiologic Science For Technologists -Stewart Carlyle Bushong The Essential Physics for Medical Imaging - Bushberg Various Slides and official websites.

73. THANK YOU!!