Unit III Creating the Image Chapter 25 Digital Radiography Objectives • Describe various digital radiography image receptor and detector systems • Explain critical elements used in the different digital radiography systems • Discuss limitations inherent in currently available digital radiography systems Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Objectives • Describe how the digital radiography histogram is acquired • Describe how the display algorithm is applied to collected data Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Objectives • Explain why digital radiography systems have greater latitude than conventional film-screen radiography systems • Analyze elements of digital radiography systems Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Objectives • Discuss what makes them prone to violation of ALARA radiation protection concepts • Explain the causes of sever digital radiography artifact problems Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Historical Development • Fuji Systems – 1980s • Today’s Systems – Several manufacturers Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Indirect Photostimulable Phosphor Imaging Plate Systems • • • • Photostimulable imaging plates Latent image production Image acquisition Reading digital radiography data Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED Photostimulable Imaging Plates • Photostimulable phosphor – PSP • Imaging plate – IP Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 10 Image Stitching • Overlapping exposures • Verified registration marks • Combine several images into one Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 57 Grid Use • Digital systems are more sensitive to scatter radiation • Grids should be used more often • Radiography of the chest – > 24-26 cm should use grid Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 58 Overexposure • Overexposure > 2X – Results in enough scatter to degrade image Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 59 Underexposure • Quantum mottle/reticulation Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 60 Direct Exposure Imaging Systems • Direct selenium flat panel imaging plate systems • Indirect silicon flat panel imaging plate systems Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 61 Direct Selenium Flat Panel Imaging Plate Systems • Amorphous selenium directly converts ionization from x-rays into electronic signal • Electronic signal received by thin film transistors (TFTs) and sent to computer Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 62 Indirect Silicon Flat Panel Imaging Plate Systems • Amorphous silicon combined with scintillator • Scintillator or intensifying screen converts x-rays to light • Amorphous silicon acts as photodiode – Converts light to electronic signal – TFTs send signal to computer Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 63 Thin Film Transistors (TFTs) • Array or matrix of pixel detectors Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 64 Charged Coupled Devices (CCD) • Photodetector typically used with a screen scintillator • Requires optical coupling by lenses or fiber optics • Electric signal from CCD sent to computer Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 65 DICOM Standard • System of computer software standards • Allows different digital imaging software to understand each other Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 66 Computed Radiography Artifacts • Acquisition artifacts ã Post acquisition artifacts ã Display artifacts Copyright â 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 67 Acquisition Artifacts • • • • • • • Phantom images Scratches Light spots Dropout Fogging Quantum mottle (reticulation) Heat blur Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 68 Heat Blur Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 69 Post Acquisition Artifacts • • • • • Algorithm artifacts Dropout artifacts Laser film transport artifacts Histogram error Nonparallel collimation Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 70 Display Artifacts • Density/brightness window level adjustments • Contrast window width adjustments • Image enhancement artifacts Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 71 ... RIGHTS RESERVED 46 CR Image Quality—Fuji System • Increased latitude compared to film/screen radiography Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 47 CR Image Quality—Fuji...Unit III Creating the Image Chapter 25 Digital Radiography Objectives • Describe various digital radiography image receptor and detector systems • Explain critical elements used... Fluoresce - or- get trapped by fluorohalide to create holes Copyright © 2006 by Thomson Delmar Learning ALL RIGHTS RESERVED 15 Hole Formation • Fluorohalide crystals trap half of the liberated electrons