1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CHAPTER 15 Creating the Digital Image

2. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins WHAT DO WE MEAN BY “DIGITAL”? Watch = analog –No further refinement in telling time beyond the hour, minute, and second Series of numbers = digital –Discreet measurement of time; carried out infinitesimally

3. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 4 BASIC FUNCTIONS FOR X-RAY IMAGE PRODUCTION 1.Acquisition 2.Processing 3.Display 4.Storage

4. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins COMPARISON OF 4 FUNCTIONS ANALOG DIGITAL LATENT IMAGE 1. ACQUISITION # X-RAYS IN PIXELS DARKROOM & PROCESSOR 2. PROCESSING IN ROOM/COMPUTER VIEWBOX 3. DISPLAY COMPUTER MONITOR FILM LIBRARY 4. STORAGE PACS

5. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins OVERVIEW OF ANALOG AND DIGITAL MAMMOGRAM EXAM

6. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DIGITAL MAMMOGRAPHY MACHINE Note the similar appearance to an analog unit.

7. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DIGITAL ARRAY AND ITS PIXELS The digital array is composed of millions of pixels.

8. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins RESOLUTION The smaller the pixel, the higher the resolution.

9. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins IMAGING MODALITIES AND MATRIX SIZE

10. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins A HUMAN HAIR IN COMPARISON TO A ROW OF PIXELS

11. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DISPLAY OF SHADES OF GRAY

12. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DISPLAY OF SHADES OF GRAY Varying optical densities of film versus how the digital system interprets optical densities

13. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DIGITAL ARRAY A. Before the exposure, all the pixels are empty. B. After exposure, pixels record number of x-rays that interacted with each pixel. C. How the detector “sees” the number of photon interactions.

14. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DIGITAL MACHINE & ITS FUNCTIONS The x-ray gantry and technologist acquisition workstation

15. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins THE TECHNOLOGIST STAYS IN THE ROOM FOR THE ENTIRE EXAM SINCE IT IS NO LONGER NECESSARY TO LEAVE TO DEVELOP FILMS IN A DARKROOM

16. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins PHOTOTIMING Digital machine phototimers rarely produce a suboptimal image. Be vigilant for dose creep.

17. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins THE DIGITAL READING ROOM A radiologist at his review station

18. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins RADIOLOGIST’S KEYPAD Rather than point, click, and drag using a mouse, some vendors supply the radiologist with a more compact keypad to streamline the interpretation process. Each button controls an image enhancement tool

19. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins IMAGE ENHANCEMENT TOOLS Hanging protocols Electronic wax pencil Annotations Window/level Zoom Inversion Electronic ruler

20. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins IMAGE ENHANCEMENT TOOLS Primarily used by the radiologist during interpretation, but many of these same features are also available to the technologist. Keep in mind that the technologist’s display monitor is not a high-resolution monitor like those available to the radiologist.

21. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins HANGING PROTOCOLS Radiologists program the computer to display images in the order and location on the monitors that they prefer.

22. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins HANGING PROTOCOLS

23. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins WAX PENCIL & ANNOTATIONS Radiologists now use an electronic wax pencil. They use an electronic annotation instead of a Post-it note stuck on a film.

24. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins WINDOW WIDTH & WINDOW CENTER The dynamic range of a digital image allows electronic changes to brightness and contrast levels without having to re-expose the patient. Better known as window/level

25. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins FULL-RESOLUTION DISPLAY The area inside the mag-box displays at the highest resolution the digital system offers. Note: This is not a magnified view.

26. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins FULL-RESOLUTION DISPLAY A. Decreased resolution required to display entire breast on monitor B. Breast displayed at full resolution; aka “zoom”

27. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins INVERSION A. What was white is now black; what was black is now white B. It is possible to use tool combinations: inversion plus zoom

28. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins ELECTRONIC RULER

29. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CAD CAD is an available option when purchasing a digital system.

30. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CONNECTIVITY Digital images move effortlessly throughout “the network.”

31. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 3 METHODS TO PRODUCE DIGITAL IMAGES Direct-to-digital –1. Indirect conversion (CsI) –2. Direct conversion (a-Se) Nondirect digital + indirect conversion –3. CR

32. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CR MAMMOGRAPHY Uses analog mammography machine Uses a special CR cassette

33. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CR MAMMOGRAPHY Image plate processor

34. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CR ADVANTAGES Less expensive –Use analog mammography machine –Mammography software upgrade for general radiology’s CR processor Two sizes of IRSD

35. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CR DISADVANTAGES Not able to adapt to future imaging technologies that require direct-to-digital platforms No improved productivity

36. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins INDIRECT CONVERSION Indirect conversion detectors work by converting x-ray photons into light.

37. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DIRECT CONVERSION X-ray photons are directly converted into an electrical charge.

38. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins EVALUATING THE DIGITAL IMAGE SNR CNR MTF DQE

39. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins SNR Signal-to-noise ratio Measures the quality of information in the image Compares level of desired signal to level of background noise Determined by the number of x-ray photons absorbed by the digital detector

40. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins CNR Contrast-to-noise ratio Ability to differentiate the x-ray attenuation co- efficiencies for all breast structures and types of tissue Essential so small differences in x-ray attenuation are visible and allow detection of cancer among the clutter of normal tissue

41. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins MTF Modulation transfer function Evaluates overall system resolution How well does the system transfer shapes/structures from the incident to the output x- ray pattern Measured by the manufacturer under perfect laboratory conditions

42. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DQE Detective quantum efficiency Best method to measure detector performance of contrast and noise Measures percentage of x-rays that strike the detector and are absorbed Compares dose