SECTION I - CHAPTER 1 DIGITAL RADIOGRAPHY: AN OVERVIEW OF THE TEXT. Exam Content Specifications 8/22/2012 RADT 3463 COMPUTERIZED IMAGING

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1 RADT COMPUTERIZED IMAGING Section I: Chapter 1 RADT 3463 Computerized Imaging 1 SECTION I - CHAPTER 1 DIGITAL RADIOGRAPHY: AN OVERVIEW OF THE TEXT RADT 3463 COMPUTERIZED IMAGING Section I: Chapter 1 RADT 3463 Computerized Imaging 2 Exam Content Specifications Section I: Chapter 1 RADT 3463 Computerized Imaging 3 1

2 Exam Content Specifications Section I: Chapter 1 RADT 3463 Computerized Imaging 4 Film/Screen Radiography VS Film/screen cassettes X-rays strike the intensifying screens expose film (latent image) Film is chemically processed Latent image becomes manifest image Filmless Imaging / Digital Imaging Any image acquisition process that produces an electronic image that can be viewed and manipulated on a computer Section I: Chapter 1 RADT 3463 Computerized Imaging 5 DIGITAL RADIOGRAPHY: A DEFINITION Uses computers to process data collection from patients Electronic detectors replace x-ray film cassette and it becomes filmless radiography Section I: Chapter 1 RADT 3463 Computerized Imaging 6 2

3 DIGITAL RADIOGRAPHY: A DEFINITION Detectors measure x-ray attenuation data from the patient The data is then converted into electronic (analog) signals The analog signals are converted into digital data for computer processing Section I: Chapter 1 RADT 3463 Computerized Imaging 7 DIGITAL RADIOGRAPHY: A DEFINITION Computer processing converts digital data into a digital image The digital image is then converted to an analog image so it can be viewed on a computer monitor The displayed image can be manipulated (annotated, enhanced, etc.) using digital image processing techniques (post-processing) Section I: Chapter 1 RADT 3463 Computerized Imaging 8 WHAT? STOP REWIND SIMPLIFY Section I: Chapter 1 RADT 3463 Computerized Imaging 9 3

4 Waveform = analog radiation, visible light, sound Electricity = electrical pulses (+/-) Is electricity analog? Digital = binary language (0, 1) the language of computers Section I: Chapter 1 RADT 3463 Computerized Imaging 10 Why? Section I: Chapter 1 RADT 3463 Computerized Imaging 11 PUT IT ALL TOGETHER! System components and steps to digital image production Section I: Chapter 1 RADT 3463 Computerized Imaging 12 4

5 FILM-BASED RADIOGRAPHY: A BRIEF REVIEW Basic steps in the Production of a Radiograph The Film Characteristic Curve Limitations of Film-Screen Radiography Section I: Chapter 1 RADT 3463 Computerized Imaging 13 BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH X-rays penetrate the patient and form a latent image on the film. Chemical processing converts latent image in a visible image. Image is displayed a view box. Section I: Chapter 1 RADT 3463 Computerized Imaging 14 BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH Density results from the amount of exposure and anatomic attenuation in an images Higher mas = more dense (overexposed) Lower mas = less dense (underexposed). Section I: Chapter 1 RADT 3463 Computerized Imaging 15 5

6 BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH Contrast is the differences in image densities. Higher kvp = Long scale = more gray shades Low contrast Lower kvp = Short scale = fewer gray shades High contrast Section I: Chapter 1 RADT 3463 Computerized Imaging 16 BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH X-ray film through chemical processing converts the transmitted radiation by the various types of tissues (tissue contrast) into film contrast. Section I: Chapter 1 RADT 3463 Computerized Imaging 17 BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH Optical Density (OD) The measurement of the amount of light transmitted through the film Describes the degree of film blackening as a result of radiation exposure Can be measured by a densitometer. Section I: Chapter 1 RADT 3463 Computerized Imaging 18 6

7 THE FILM CHARACTERISTIC CURVE Characteristic Curve or the Hurter-Driffield (H and D) curve describes film contrast. The curve is a plot of the OD to the logarithm of the relative exposure (radiation exposure) to make the radiograph. Section I: Chapter 1 RADT 3463 Computerized Imaging 19 THE FILM CHARACTERISTIC CURVE The curve indicates the degree of contrast (different densities) that a film can display using a range of exposures. The curve has three main segments: Toe Slope (straight-line portion) Shoulder. Section I: Chapter 1 RADT 3463 Computerized Imaging 20 THE FILM CHARACTERISTIC CURVE Toe = underexposure OD = ~ Slope = acceptable exposure = useful range of exposures OD = Shoulder = overexposure OD = >3.2 Base plus fog =no exposure is used OD = 0.1 to 0.2 Section I: Chapter 1 RADT 3463 Computerized Imaging 21 7

8 THE FILM CHARACTERISTIC CURVE Four other factors that can be described using the characteristic curve: Film Speed Average Gradient Film Gamma Film Latitude Let s talk briefly about each Section I: Chapter 1 RADT 3463 Computerized Imaging 22 THE FILM CHARACTERISTIC CURVE Film Speed Sensitivity of film to radiation Fast film ( higher speed) = less exposure Slow film (lower speed) = more exposure Bonus: Which one would you use for high detail imaging? Section I: Chapter 1 RADT 3463 Computerized Imaging 23 THE FILM CHARACTERISTIC CURVE Average Gradient slope of the straight-line region of a sensitometric curve Long scale contrast when film has average gradient of 3.0 Short scale contrast when film has average gradient of 2.7) Section I: Chapter 1 RADT 3463 Computerized Imaging 24 8

9 THE FILM CHARACTERISTIC CURVE Film Gamma Calculated from points surrounding optical density of 1.0 of sensitometry curve Used for information about contrast by type of film Section I: Chapter 1 RADT 3463 Computerized Imaging 25 THE FILM CHARACTERISTIC CURVE Film Latitude Wide exposure latitude = ability to use a wide range of exposures Narrow exposure latitude means it respond to small range of exposures. Section I: Chapter 1 RADT 3463 Computerized Imaging 26 LIMITATIONS OF FILM-SCREEN RADIOGRAPHY Problem: poor quality radiograph if the initial radiation exposure was not accurate. Too high an exposure = overexposed radiograph Too low an exposure = underexposed radiograph Solution: Repeat radiograph to obtain one of acceptable quality for interpretation Drawbacks: Repeating radiographs increases radiation exposure to the patient Section I: Chapter 1 RADT 3463 Computerized Imaging 27 9

10 LIMITATIONS OF FILM-SCREEN RADIOGRAPHY Limitation 1: Film based imaging is limited to its contrast resolution Film-screen cannot show differences in tissue contrast less than 10%. Contrast Resolution mm at 0.5% difference Radiography 10 Nuclear Medicine 20 Sonography 10 Computed Tomography 4 Magnetic Resonance Imaging 1 Spatial resolution for film-screen radiography (5-15 line pairs/mm) is higher than other imaging modalities. (more on this later) Section I: Chapter 1 RADT 3463 Computerized Imaging 28 LIMITATIONS OF FILM-SCREEN RADIOGRAPHY Limitation 2: The film s optical range and contrast are fixed and limited and cannot be manipulated to enhance image quality. Exposure technique factors and integrity of chemical processing determine optical range and contrast. To change displayed images, a repeat radiograph increases patient s radiation dose. Section I: Chapter 1 RADT 3463 Computerized Imaging 29 LIMITATIONS OF FILM-SCREEN RADIOGRAPHY Limitation 3: To archive, radiographs are usually stored in envelopes and files in a large room. Manual handling is required for archiving and retrieving each patient s radiography examination. Section I: Chapter 1 RADT 3463 Computerized Imaging 30 10

11 A DIGITAL RADIOGRAPHIC IMAGING SYSTEM: Data Acquisition Computer Data Processing Image Display and Post Processing Image Storage Image and Data Communications Image and Informational Management MAJOR COMPONENTS Section I: Chapter 1 RADT 3463 Computerized Imaging 31 DATA ACQUISITION Section I: Chapter 1 RADT 3463 Computerized Imaging 32 COMPUTER DATA PROCESSING Section I: Chapter 1 RADT 3463 Computerized Imaging 33 11

12 IMAGE DISPLAY AND POST PROCESSING To view a digital image, it must be converted into an analog signal This occurs in the digital-to-analog converter (DAC). The image can now be viewed in multiple ways at the viewers discretion Section I: Chapter 1 RADT 3463 Computerized Imaging 34 IMAGE DISPLAY AND POST PROCESSING Using post-processing, the displayed image can be manipulated to: Reduce noise Enhance image sharpness Change contrast Stitch images together to form one image Gray scale mapping Annotate Section I: Chapter 1 RADT 3463 Computerized Imaging 35 Image are archived and stored for retrospective analysis and for medico-legal purposes. IMAGE STORAGE Old Standard of Optical CD DVD Permanent Hard Drive New Plug and Play Entries Flash Memory / Memory Cards) USB Jump drive Portable hard drives Section I: Chapter 1 RADT 3463 Computerized Imaging 36 12

13 IMAGE STORAGE Long term storage of digital images needs to rely on large capacity servers such as a RAID (redundant array of independent disks) system. Short-term archival systems are deleted after a period of time defined by the institution. MEDICAL IMAGE DIGITAL FILE SIZE IMAGE SIZE EXAMINATION SIZE Nuclear Medicine 0.25 MB 5 MB Diagnostic Sonography 0.25 MB 8 MB Magnetic Resonance Imaging 0.25 MB 12 MB Computed tomography 0.5 MB 20 MB Digital Radiography 5 MB 20 MB Digital Mammography 10 MB 60 MB Section I: Chapter 1 RADT 3463 Computerized Imaging 37 IMAGE AND DATA COMMUNICATIONS Images need to be transmitted from the acquisition phase to the display/viewing and storage phase. HIS - Hospital Information System are now being integrated with the PACS by computer networks RIS - Radiology Information Systems can use PACS systems are being used for storing/archiving and communicating images PACS - Picture Archiving and Communication Systems store and archive images Section I: Chapter 1 RADT 3463 Computerized Imaging 38 IMAGE AND DATA COMMUNICATIONS Networks: LANS - local area networks can be used within a hospital. WANS - wide area networks are used for sites outside and remote of the hospital. Language: Effective management and standards of patient information DICOM - Digital Imaging and Communications in Medicine and HL-7 Health Level-7) IHE Integrating the Healthcare Enterprise (ACR, RSNA, and HIMSS) Section I: Chapter 1 RADT 3463 Computerized Imaging 39 13

14 IMAGE AND DATA COMMUNICATIONS Image Compression Storing data in a format that requires less space than usual. Compression techniques are distinguished by whether they remove detail and color from the image Crucial to radiology and teleradiology because of large image file sizes. The process of compacting an image by removing redundant information. Section I: Chapter 1 RADT 3463 Computerized Imaging 40 IMAGE AND DATA COMMUNICATIONS Image Compression There are two main types of compression: Lossless compression - on decompression, the original is restored in every detail. Lossy (lossee) compression - unnecessary(?) detail is thrown away Section I: Chapter 1 RADT 3463 Computerized Imaging 41 DIGITAL RADIOGRAPHY MODALITIES Computed Radiography (CR) Flat-Panel Display Radiography (DR) Digital Mammography Digital Fluoroscopy Section I: Chapter 1 RADT 3463 Computerized Imaging 42 14

15 COMPUTED RADIOGRAPHY (CR) Fundamental steps in the production of a CR image. Section I: Chapter 1 RADT 3463 Computerized Imaging 43 FLAT-PANEL DIGITAL RADIOGRAPHY (DR) Digital detector is designed as a flat-panel Two Categories: Indirect conversion digital radiography systems 1. Array of electronic elements 2. Charge-coupled devices (CCDs) Direct conversion digital radiography systems. Section I: Chapter 1 RADT 3463 Computerized Imaging 44 FLAT-PANEL DIGITAL RADIOGRAPHY (DR) Indirect (electronic elements) X-rays are converted to light using a phosphor such as cesium iodide. Emitted light from the phosphor falls on a matrix array of electronic elements to create and store electrical charges in direct proportion to X-ray exposure. Charges produce electrical signals, which are digitized to produce an image. Section I: Chapter 1 RADT 3463 Computerized Imaging 45 15

16 FLAT-PANEL DIGITAL RADIOGRAPHY (DR) Indirect (charge-coupled device) Uses an array of chargecoupled devices (CCDs) which are coupled to a scintillator phosphor, cesium iodide X-rays fall on the phosphor to produce light, which then falls on the CCD array, which in turn converts the light into electrical signals that are then digitized and processed to produce an image. Section I: Chapter 1 RADT 3463 Computerized Imaging 46 FLAT-PANEL DIGITAL RADIOGRAPHY (DR) Direct Detectors convert x-rays directly into electrical signals. X-rays fall on a photoconductor (e.g.- selenium) that is coupled to a matrix array of electronic elements to produce electrical signals. These signals are digitized and processed to produce an image. Section I: Chapter 1 RADT 3463 Computerized Imaging 47 FLAT-PANEL DIGITAL RADIOGRAPHY (DR) Advantages Flat-panel digital detector can be erased and ready to be reused. High detective quantum efficiency (DQE) What? Spatial resolution comparable to CR systems. Characteristic response to radiation exposure with wide exposure latitude fundamentally different to the film characteristic curve. Wide exposure latitude will produce acceptable images even when the input exposure is low or high. Section I: Chapter 1 RADT 3463 Computerized Imaging 48 16

17 DIGITAL MAMMOGRAPHY Benefits Overcomes limitations of technique in filmscreen mammography Post-processing tools allows enhancement image for interpretation Uses computer-aided diagnosis (CAD) software to enhance detection of microcalcifications and malignant lesions Provides the "second reader Section I: Chapter 1 RADT 3463 Computerized Imaging 49 DIGITAL FLUOROSCOPY Major goal of digital fluoroscopy Use digital imaging processing software to improve the perception of contrast resolution, compared to conventional fluoroscopy Advantages Gray-scale processing Temporal frame averaging Edge enhancement Produces dynamic images acquired in real time Section I: Chapter 1 RADT 3463 Computerized Imaging 50 DIGITAL FLUOROSCOPY Section I: Chapter 1 RADT 3463 Computerized Imaging 51 17

18 DIGITAL FLUOROSCOPY Application Digital subtraction angiography (DSA) in which pre-contrast and post-contrast images can be digitally subtracted in real time. Why? Improve the perception of low-contrast vessels by subtracting or removing the tissues (bones) that interfere with visualization of vascular structures. Two subtraction techniques Temporal subtraction Energy subtraction Section I: Chapter 1 RADT 3463 Computerized Imaging 52 DIGITAL FLUOROSCOPY Temporal subtraction, in which images are subtracted in time Section I: Chapter 1 RADT 3463 Computerized Imaging 53 DIGITAL FLUOROSCOPY Energy subtraction, in which images are subtracted using different kilovoltages. Section I: Chapter 1 RADT 3463 Computerized Imaging 54 18

19 PICTURE ARCHIVING AND COMMUNICATION SYSTEMS PACS = IMACS (image management and communications systems Digital images must be Displayed for interpretation Stored and archived for medico-legal purpose Stored for retrospective analysis Transmitted to remote locations Section I: Chapter 1 RADT 3463 Computerized Imaging 55 Major components include: Image acquisition devices PACS computer Devices called interfaces Display workstations All should be connected and linked to HIS and RIS MAJOR SYSTEM COMPONENTS Section I: Chapter 1 RADT 3463 Computerized Imaging 56 PICTURE ARCHIVING AND COMMUNICATION SYSTEMS MAJOR SYSTEM COMPONENTS PACS systems contains confidential patient data and information Data security is of central importance (HIPAA) Health Insurance Portability and Accountability Act Interfaces Facilitate easy communication between the image acquisition modalities and the HIS/RIS with the PACS computer Allow individuals to use the World Wide Web to access the PACS computer. Section I: Chapter 1 RADT 3463 Computerized Imaging 57 19

20 QUALITY ASSURANCE IN DIGITAL RADIOGRAPHY QA and QC procedures are effective strategies to ensure continuous quality improvement to: Ensure patients are exposed to minimum radiation using the ALARA (as low as reasonably achievable) philosophy. Produce optimum image quality for diagnosis. Reduce the costs of radiology operations. Section I: Chapter 1 RADT 3463 Computerized Imaging 58 MEDICAL IMAGING INFORMATICS Information Technology (IT) concepts are used for Digital image acquisition technologies Digital image processing Digital image display Storage and archiving Digital image communications Rapidly growing field degrees in informatics Section I: Chapter 1 RADT 3463 Computerized Imaging 59 WHAT IS MEDICAL IMAGING INFORMATICS? IT (Information Technology) helps use images for: Diagnosis Assessment and planning Guidance of procedures Communication Education Training Research. Section I: Chapter 1 RADT 3463 Computerized Imaging 60 20

21 WHAT IS MEDICAL IMAGING INFORMATICS? IT involves these topics: Information systems Standards for communicating (text and images) Computer communication networks Web technology Image and text handling Privacy, security, and confidentiality issues Digital image processing Payroll Section I: Chapter 1 RADT 3463 Computerized Imaging 61 THE TECHNOLOGIST AS INFORMATICIST Radiographers need skills related to IT Radiology Departments need a PACS administrator (IT administrator) Function is dedicated to ensuring the integrity of the PACS. Radiographers need to learn the skills to become a informaticist Section I: Chapter 1 RADT 3463 Computerized Imaging 62 SECOND LOOK: Sprawls Educational Foundation Section I: Chapter 1 RADT 3463 Computerized Imaging 63 21

22 QUESTIONS?? What lies behind us and what lies before us are small matters compared to what lies within us. Ralph Waldo Emerson Section I: Chapter 1 RADT 3463 Computerized Imaging 64 22