digital radiography

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Information about digital radiography

Published on July 16, 2008

Author: arunrr


Slide 1: Digital radiography - An Insight An introduction : An introduction Plain radiography has been the backbone of radilogy for many years. 70 – 80% of a radiology dept workload comprises of plain radiography. Plain X-rays are the only ‘ non- digital’ imaging modalities in use today. Most of the imaging modalities like Ultrasound, CT, MRI, DSA etc are already have integrated digital techniques. For a fully digital ‘filmless’ dept plain films also need to be taken in digital format. RADIOGRAPHY It is an art and science of recording images produced by X-rays on film : RADIOGRAPHY It is an art and science of recording images produced by X-rays on film Film act as Image receptor Display medium Permanent record Radiography : Radiography Transmitted X-rays Limitations with conventional films : Limitations with conventional films Limited exposure latitude resulting in frequent over and underexposure of films. Chemical processing is essential and time , labour intensive. Loss of quality and significant cost involved during Duplication Transmission Storage WHY DIGITAL IMAGES : WHY DIGITAL IMAGES Screen-Film Radiology Image quality is “Built-in” characteristic of film Film is acquisition, display and archive medium Dose is determined by screen-film speed Digital Radiography Image quality is dependent on SNR Separation of acquisition, display, and archive Dose is variable and dependent on required SNR WHY DIGITAL IMAGES : WHY DIGITAL IMAGES More than 60% of manpower of radiology department is involved in plain film radiology. Digital imaging has potential to improve efficiency within radiology department. Improved working, both intra & inter department. Dose reduction is strongly associated with digital radiography. Digitalization of radiograph (through CR/DR) acts as a medium for effective . Data manipulation Data transfer ( PACS, telemedicine) Data storage (space saving) Fashionable, moving ahead with changing technologies. Inevitable ? With telemedicine growing up . Adv –Digital radiography : Adv –Digital radiography Robustness. Consistency. Flexibility. Featured contents. Communication. DIGITALISATION OF CONVENTIONAL FILMS : DIGITALISATION OF CONVENTIONAL FILMS Slide 10: History of Digital Imaging Basics of Digital Language : 11 Basics of Digital Language Digital information : 12 Digital information Binary Number—0 & 1 Binary Digits – Bits Sequence of Bits– Word Sequence of 8 Bits--Byte Byte : 13 Byte The basic unit of binary coded information Kilobyte—210 – 1024 bites Megabyte—1024 times1024bites Performance parameters : Performance parameters Pixel: Smallest complete sample of an image. Has a varied set of tones in shades of white/ black/grey. Expressed in binary codes (bits). Size of the pixel : Smaller the size , better resolution. CR- 50 to 200 microns, DR- 100 to 200 microns, DM- 50 to 100 microns. Gray Scale: Shades of Gray in between pure black and pure white. Bit Depth: No of shades to define each pixel ,measured as no of bits. Larger the depth, incr gray scale and large file size. Performance Parameters(contd..) : Performance Parameters(contd..) Performance Parameters(contd..) : Spatial Resolution: finer details, diff objects in an image. Depends on sampling frequency and no of pixels. expressed in lp/mm. Contrast Resolution: Color or gray scale differentiation. Indicate the no of shades of grey that a detector can capture. File Size. Performance Parameters(contd..) Digital Image Processor : Digital Image Processor Slide 20: Computer Storage Viewing/Displaying Digital Format Analogue Format Image information Analogue Form Analogue-to-Digital Converter Digital-to-Analogue Converter Digital Radiography : Digital Radiography Indirect digital Radiography Film Digitization Computed Radiography Direct digital Radiography CCD Cameras CMOS Cameras Thin Film Transistor (TFT) Flat Panel Arrays Depending on mode of acquisition and capture of the x-ray image with/without user intervention. Slide 24: 24 Slide 25: 25 Slide 26: 26 Slide 27: Cassettes Slide 28: 28 Slide 29: 29 CR – Basic Principle Slide 30: 30 Slide 31: 31 Slide 32: 32 IMAGING PLATES : IMAGING PLATES PROTECTIVE LAYER PHOSPHOR LIGHT REFLECTIVE LAYER SUPPORT LIGHT SHEILDING LAYER BRACODE LABEL BACKING LAYER CONDUCTIVE LAYER IMAGING PLATES : IMAGING PLATES Photostimulable Storage Phosphor plates. Standard grade imaging plate has 210 um thick phosphor layer with a reflective backing on a polyester base Thin protective layer Phosphor layer (Barium Fluorohalide contained in binder provides photo-stimulable phosphor) Conduction layer (reduces problem caused by electrostatic charges by absorbing light and increase image sharpness) IMAGING PLATES : IMAGING PLATES Light reflective Layer Support Light shielding layer (Carbon particle in binder) Bracode label (Serial no. for identification) Backing layer. Slide 38: 38 Main plus points : 39 Main plus points very rapid access to digital images wherever radiography is performed. image quality will exceed that of both screen-film receptors and CR systems improvements in productivity Direct digital Radiography : 40 Direct digital Radiography FPD Systems CCD Based systems Slot Scanning systems Photon counting Type FPD Systems : FPD Systems Usage of TFT Arrays-Thin Film Transistor arrays. TFT arrays are made of a-Si etched with detector element of 70-200 micrometer on a glass substrate. Element has capacitor and switching transistor for active readout of charges from the detector element. Layered with a x-ray convertor material to cpmplete the FPD. Two types- a. Direct conversion type using a photoconductor b. Indirect conversion type using photoscintillatior/phosphor screen. Slide 42: 42 Slide 43: 43 Slide 44: 44 Slide 45: 45 Slide 46: 46 Slide 49: 49 Slide 50: 50 THE CHARGE COUPLED DEVICE (CCD) array of light sensitive detector elements on a silicon chip Slide 51: 51 Slide 52: 52 Slot Scanning DR systems : Slot Scanning DR systems Narrow x-ray fan beam and CCD array detector mechanically linked and scan along the long axis of patient Slot Scanning DR systems : Slot Scanning DR systems Scan time - depends on area covered - 2 to 30 seconds Advantage - no grid required - lower radiation dose - large area can be covered Disadvantage - long time for acquisition - motion artifact due to long exp - excessive tube loading Photon counting type DR systems : Photon counting type DR systems Similar to slot scanning type but uses a diff multi slit detector made of silicon,somewhat similar in principle to direct FPD. Voltage of 100 volts applied across the array of si crystals. Absorbed x-rays produce electrons and holes. The events are counted in a timer corres to spatial loc of the x-ray beam sweep. Used in mammography ,produces significant SNR. Slide 58: 58 Parts of FPD DR System : Parts of FPD DR System Slide 60: 60 IMAGE PROCESSING : IMAGE PROCESSING Computed manipulation of recorded data to change appearance of original data for practical use Control density/contrast changes Digital unsharp masking to produce edge enhancement Reversal of gray scale Tone processing-changing characteristic curve of film and digital data on imaging plate at desirable level of density and contrast Frequency processing –corresponds to control of sharpness of objects on image IMAGE PROCESSING : IMAGE PROCESSING Noise compensation (Lungs) Structure boost (Weakly contrasting str. Become better visible) Structure preference Multi frequency processing Manipulation of Images : Manipulation of Images Manipulation of Images : Manipulation of Images CHEST & DR : CHEST & DR Control of displayed optical density of radiographs With dynamic range control processing, it improves visibility of tubes and lines superimposed on mediastenum Visibility of normal lung structure improves should not be mistaken for ILD Solid state flat panel selenium based detectors help to decrease the image noise and 50% reduction of dose Chest DR : Chest DR MAMMOGRAM &DR : MAMMOGRAM &DR Wide exposure latitude (for dense and fatty breasts) Sufficient image contrast to visualize small, low density masses and tiny clusters of calcification Contrast Conv v/s Digital : Contrast Conv v/s Digital MUSCULOSKELETAL IMAGING & DR : MUSCULOSKELETAL IMAGING & DR Emergency room setting, less no. of repeat exposure, better details, Wide dynamic range and post processing for thick body parts (DL spine, cervicodorsal spine) Area of complex anatomy (Lat view of hip, Mandible, TM joint, Sternoclavicular joint) Rebirth of arthroscopy procedure GI Imaging & DR : GI Imaging & DR Faster acquisition, instant display and immediate post processing Reduced motion blur Reduced re-exposures Reduced down time between two exposure –better evaluation pharynx, esophagus Slide 71: 71 RECENT & FUTURE DEVELOPMENT OF DR : RECENT & FUTURE DEVELOPMENT OF DR INTEGRATED CR SYSTEMS-TABLES AND CHEST STANDS DUAL ENERGY IMAGING Slide 73: Tomosynthesis – like multi-cassette tomography addition of images after pixel shift Dual energy imaging - Soft tissues & bones can be separated Mobile DR – Usually 17 x 14 inch detector connected by a cable to mobile X-ray system having a monitor CAD RECENT & FUTURE DEVELOPMENT OF DR Tomosynthesis : Tomosynthesis Like Tomography No detector move Shift & add pixels Tomosynthesis - Chest : Tomosynthesis - Chest Tomosynthesis - Breast : Tomosynthesis - Breast Image Stitching : Image Stitching Image Stitching- Spine, Legs : Image Stitching- Spine, Legs CR v/s DR : CR v/s DR Attribute CR DR - Positioning flexibility ++++ + - Direct replacement of FSR ++++ + - Spatial Resolution ++ +++ - DQE ++ +++ - Patient throughput ++ ++++ - System Cost ++++ + - Ease of use + +++ - X-ray system integration + ++++ - PACS compatibility ++ +++ Image Quality ComparisonDR CR : Image Quality ComparisonDR CR Combined CR & DR : Combined CR & DR Slide 83: 83 Slide 84: 84 PACS and DICOM : PACS and DICOM THE ROLE OF PACS : A Picture Archiving and Communication System (PACS) aims to replace conventional analogue film and paper clinical request forms and reports with a completely computerized electronic network whereby digital images are viewed on monitors in conjunction with the clinical details of the patient and the associated radiological report displayed in electronic format. The ROLE OF DICOM: Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a picture archiving and communication system (PACS). The different devices come with DICOM conformance statements which clearly state the DICOM classes they support. DICOM has been widely adopted by hospitals . References : References Verma BS, Indrajit IK. Advent of digital radiography Part 1 & Part 2 . IJRI 2008. Verma BS, Indrajit IK. Digital Imaging in radiology practice: An introduction to few fundamental concepts. IJRI 2007 ; 17. Chotas et al. Principles of digital radiography with large area electronically readable detectors: A review of basics. Digital radiography. ppt from Internet. Basic Principles of flat panel radiography by Padovani. Flat panel X-ray detector by Jean Chabbel. An overview of digital imaging systems for radiography and flouroscopy. Slide 88: Thank you

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