1 / 47

George David Associate Professor of Radiology Medical College of Georgia

Artifacts on Computed Radiography (CR), & Digital Radiography (DR) Images. George David Associate Professor of Radiology Medical College of Georgia. Quick Review of Technology. Computed Radiography (CR). Re-usable metal imaging plates replace film & cassette. CR Exposure.

Download Presentation

George David Associate Professor of Radiology Medical College of Georgia

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

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

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

  15. Artifacts in Digital Radiography

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

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

  18. 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

  19. 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

  20. Look-up Table / Image Processing Errors

  21. 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

  22. 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

  23. 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

  24. More Uberschwinger

  25. 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

  26. Low Exposure Results in Image Noise • Increasing mAs

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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. CR What are white lines?

  34. 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

  35. 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

  36. 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

  37. 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

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

  39. 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

  40. Tape artifact seen after tape removed

  41. Interferance

  42. 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.

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

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

  45. The End ?

More Related