Bushong: Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition

2Answers to Challenge Questions

Bushong: Radiologic Science for Technologists: Physics, Biology, and Protection, 8th EditionAnswers to Challenge QuestionsChapter 28: Digital Fluoroscopy1. a.Method of temporal subtraction that results in successive subtraction images of contrast-filled vessels.

b. Matching two or more images in space.

c. Time required for the x-ray tube to be switched on and reach the selected level of kVp and mA.

d. Temporal subtraction refers to a number of computer-assisted techniques whereby an image obtained at one time is subtracted from an image obtained at a later time. Energy subtraction uses two x-ray beams alternately to provide a subtraction image resulting from differences in photoelectric interaction. Hybrid subtraction combines temporal- and energy-subtraction techniques.

e. Charged-coupled device.

f. Region of interest.

g. One line at a time sequential instead of interlaced.

h. Sum multiple images to increase S/N.

i. Connecting point on a system.

j. Picture Archiving and Communications System.

2. Improved contrast resolution because of postprocessing procedures, instant access to spot films, signal-to-noise improvement by frame averaging, and instant image subtraction for contrast studies.

3. The acquisition of a series of images is followed by contrast administration, followed by another series of images. The precontrast and postcontrast images can be summed to improve the signal-to-noise ratio and then subtracted from one another to produce an angiogram or other such image of contrast-filled anatomy.

4. Interlaced = alternate video lines. Progressive = sequential video lines.

5. There are spurious electrical signals resulting from small stray electrical current and thermally induced stray currents. Cooling electronics always reduces electronic noise.

6. Subtraction of two images at different kVp.

7. The number of video lines and bandwith of the image monitor.8. 0.45 mm 0.45 mm.

9. That each pixel can contain up to 4096 values, each value representing a different shade of gray.

10. The spatial resolution of all digital images is pixel limited. We cannot image something smaller than a pixel. Theoretically, therefore, for digital fluoroscopy a limited spatial resolution is field of view divided by matrix size.

11. Approximately 1.6 MB.

12. 0.12 mm.

13. Computers, monitors, transmission medium.

14. A computer an A to D converter and a D to A converter.15. Dose should be the same but experience shows it to be higher because of ease of image acquisition.

16. 33 ms.

17. Approximately 70 kVp.

18. Direct digital, no lag, long life.

19. Postprocessing to reregister the image.

20. High SNR results in better contrast.

Copyright 2004 by Mosby, Inc.

Copyright 2004 by Mosby, Inc.