George David Associate Professor of Radiology Medical College of Georgia

1. Artifacts on Computed Radiography (CR), & Digital Radiography (DR) Images George DavidAssociate Professor of Radiology Medical College of Georgia

2. Quick Review of Technology

3. Computed Radiography (CR) • Re-usable metal imaging plates replace film & cassette

4. CR Exposure

5. Reading Imaging Plate • Reader scans plate with laser light using rotating mirror • Plate pulled through scanner by rollers • Light given off by plate measured byPM tube &recorded by computer

6. CR Operation • after read-out, plate erased using a bright light • plate can be erased virtually without limit • Plate life defined not by erasure cycles but by physical wear

7. CR Latitude • Very large • Plate responds to decades of input exposure • Computer scale inputs exposure to viewable densities

8. CR Very Sensitive to Scatter

9. Digital Radiography (DR) • Digital bucky incorporated into equipment • Direct digital output • High Lattitude

10. Raw Data Image • Unprocessed image as read from receptor • Not a readable diagnostic image • Requires computer processing before presentation as finished radiograph

11. * Enhancing Raw Image (Image Segmentation) • Identify collimated image border • Separate raw radiation from anatomy • Apply appropriate tone-scale to image • Create look-up table (LUT) • Maps pixel value to display gray shade This process is specific to a particular body part and projection

12. Image Segmentation • Establish location of collimated border • Define anatomic region • Produce look-up table based on histogram from anatomical area • Body part & projection specific

14. Gross Overexposure • Properly exposed • 8X increase in mAs

15. Gross Underexposure • Properly exposed • mAs reduced by ~ 100

16. Artifacts in Digital Radiography

17. Artifact Categories • Non-digital-related technical errors • Look-up table / image processing errors • Exposure artifacts • CR artifacts • DR artifacts • Interference artifacts • Display artifacts

18. Radiography ArtifactsDigital or Not • Mis-positioning • Motion • Incorrect patient ID • Double exposures • Grid cut-off

19. Radiography http://radiographics.rsnajnls.org/cgi/reprint/11/2/307?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=grid+artifacts&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT No grid102 cm SID .33R ESE Grid122 cm SID 2.2 R ESE

20. References • “Digital Radiography Artifacts”from Veterinary Radiology & Ultrasound • Wm Tod Drost, David J. Reese, William J. Hornof • “Artifacts in Digital Radiography” from Veterinary Radiology & Ultrasound • David A. Jimenez, Lauara J. Armbrust, Robert T. O’Brien, David S. Biller • Radiographics • http://www.slideshare.net/ricksw78/digital-radiography

21. Look-up Table / Image Processing Errors

22. CR Diagonal collimation caused algorithm to improperly recognize collimated area Gonadal shields can fool algorithm 2 exposures on one plate can fool algorithm http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

23. CR Chest incorrectly specified by technologist to CR reader as lumbar spine http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

24. Uberschwinger Artifact • Causes appearance of fine black line halo • Result of implementation of edge enhancement • Can be mistaken for evidence of loosening of orthpedic device • Can mimic pneumothorax

25. More Uberschwinger

27. Clipping • Occurs because of applying LUT during pre-processing • Kodak recommends technologists do not window/level on qc workstation. • Raw data: 12-14 bit image • LUT during pre-processing: Only 10-12 bits saved • Information may be lost

28. Low Exposure Results in Image Noise • Increasing mAs

29. Exposure Artifact • VERY high exposures can result in saturation • Maximum detector response reached • No response to increased dose • Uniformly dark • Cannot be windowed/leveled

30. CR Artifacts • Fading • Light leak • Physical damage to imaging plates • Cracks, scuffs, scratches • Contamination • Dust / dirt • Dirt in reader • Highly sensitive to scatter radiation • Upside-down insertion into bucky

31. CR Artifact: Fading • CR latent image consists of excited electrons stuck in high energy state orbits • Over time if image not read then electrons fall back to ground energy state • Several days required before significant fading occurs

32. CR Artifact: Light Leak in Cassette • CR plates erased by exposure to bright light • Light leaks in cassette can cause partial premature erasure of plate

33. CR Dirt Artifact On imaging plate during reading In reader Can get on plate Can be blocked in light guide of reader White line in direction of plate movement CR readers require periodic preventive maintenance & cleaning http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

34. CR Dirt on CR plate. Right image repeated on screen-film http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

35. CR What are white lines?

36. CR Cracks on image plate due to mechanical wear http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

37. CR http://radiographics.rsnajnls.org/cgi/reprint/11/5/795?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=artifact&searchid=1&FIRSTINDEX=10&sortspec=relevance&resourcetype=HWCIT

38. R o t a t i n g M i r r o r P M T u b e L i g h t L a s e r A n a l o g / D i g i t a l C o m p u t e r B e a m s c a n n e d Plate Travel a c r o s s f i l m CR Transport problems in CR reader

39. CR Plates are Very Susceptible to Scatter • Do not keep plates in room during other exposures • Do not store where likely to receive scatter • Erase plate before use if it has been sitting a long time

40. DR Artifacts • Dead detector elements • Software correction to a point… • R/F interference • Detector shielded to prevent this • Periodic pattern

41. DR Artifacts: Spatial Variations in Background Signal & Gain • Addressed by acquiring flood and building calibration mask • Similar to uniformity correction in nuclear medicine • Artifact results if attenuator in beam during calibration, then removed • Contrast • Tape

42. Tape artifact seen after tape removed

43. Interferance

44. CR Grid Interference • 103 lines / inch grids have same frequency as CR laser scanner. This can cause “Moire” pattern artifact • Align grid lines perpendicular to scan orientation whenever possible • Reduces chances of artifacts caused by laser scanner.

45. Object Interferance Moire effect because of interference between scan frequency of matrix and spiral

46. Display • Poor calibration • Dead pixels • Backlight issues

47. The End ?