RT 244 -12 Wk 14 Digital Artifacts & Imaging ERRORS

1. RT 244 -12 Wk 14Digital Artifacts & Imaging ERRORS The advantages of CR are its large dynamic range, digital format, portability, and post-processing capability But not PERFECT –Imaging Errors can still occur See NOTES at bottom of slides for additional information Some information obtained from: AR Online » Current Issue »Artifacts and misadventures in digital radiographyBy Charles E. Willis, PhD, DABR; Stephen K. Thompson, MS, DABR; S. Jeff Shepard, MS, DABRVolume: 33 Number: 1 January 2004

2. Artifacts • Any irregularity on an image that is not caused by proper shadowing of tissue by the primary x-ray beam. • Are undesirable optical densities or blemishes on a radiograph. • Can be very interesting at times. You become the detective, what caused that?

3. CR artifacts require special attention. • This is due to the fact that CR artifacts may be produced from various components of the CR system itself • Artifacts may also be generated by the users who are not aware of the proper imaging techniques or selection of appropriate image processing protocols • Since CR is also very sensitive to scattered radiation, it is vital that anti-scattered grids be used as in conventional radiography. • Radiographers should be concerned since these may generate unwanted artifacts that could not be corrected by any image processing algorithm.

4. Artifact Classification Review of Film/Screen

5. Artifact Classification Digital – CR & DR

6. OPTIMIZATION OF CR IMAGES Quality of CR images • Technologists are the key persons • delivering good quality radiographs • dose given to the patients. • CR images can NOT always be adjusted after exposing • CRITICAL to CR/DR Imaging is Technique, Positioning Collimation.

7. Optimization of a CR image quality may be achieved by optimizing the following factors • OBJECT ARTIFACTS: • Positioning and collimation • Exposure techniques • Image processing selection • Lifetime of the PSP

8. CR Artifacts • Positioning errors • Collimation errors • Backscatter radiation • LUT selection/histogram

9. Positioning of Part/ Collimation • 2 or more two projections on one IR • Is not a good practice with CR technique, • since double or multiple exposures on a single PSP) can lead to a failure of the image processing software to detect the image boundary. • Matching the positioning and collimation with the image processing parameters is also crucial. • Image processing will eventually fail to process since the input information is totally different.

11. Errors in collimation can cause mistakes in detection of the boundary, with a dramatic loss of image contrast

13. Positioning Errors

14. Collimation Errors

16. Loss of contrast due to partitioning errors

18. Alignment Error: Same technique, different centering and collimation S# 592 S# 664

20. 􀂡2 on 24 X 30 􀁹Technique adjusted 2 on 24 X 30 􀁹Same technique 􀁹Rescaling error.

21. Single field per plate - better

22. What is the problem?

23. Placement of gonadal shields is no longer trivial, but may adversely affect image quality.

24. Software to compensate for metal in patient

25. Same pt – what improved this image?

26. Acquiring good quality images • Regardless of the acquisition technology, good radiographic images can be produced only when certain fundamental requirements are met. • Appropriate radiographic technique must be used, • proper tube potential (kVp), • beam current (mAs), • source-to-image distance (SID), • collimation, • alignment of the X-ray central ray, • and positioning of detector and subject for the specific anatomic projection.

27. Exposure techniques • CR may be operated at a different film speed, and then optimizing the exposure technique accordingly. • Existing CR has a speed similar to medium speed film-screen system (200 -400) while spatial resolution is still generally inferior • Proper selection of an image processing algorithm specific to each type of x-ray examination is thus important. • The technical skills of radiographers definitely play a crucial role in determining the quality of the radiographic image.

28. Exposure factor “creep" • related to the wide exposure latitude of DR. • noise in DR images exposed at one-fourth to one-half of the appropriate level. • artifacts are generally not apparent until the exposure exceeds 10 times the appropriate level. • Technologists avoid repeating an underexposed study by routinely increasing the radiographic technique. • Thus, the potential for gross overexposure exists in DR. Image optical density (OD), the usual indicator of proper exposure, is arbitrary in DR. • Managment of exposure factor in DR must rely on the value of a derived exposure indicator

29. Errors in the selection of the anatomic projection can cause inappropriate processing

30. Wrong Algorithm

31. Over/Under Exposed • Even though a CR image may be adjusted to improve the image visibility in the cases of over- or under-exposures, it would still be impossible for an image processing to improve the visibility of clinical features that were not available in the raw image.

35. the same image now shows acceptable image quality as a result of proper selection of image processing. • Example of artifacts in CR an image with loss of contrast as a result of improper selection of image processing;

38. Too many X-rays are a disservice to the patient and may also produce poor images (Figure 3).

39. Whether from underexposure or misalignment of a scatter reduction grid, too few X-rays produce noisy images

40. Different exam parametersin different rooms

41. Double exposure is a classic operator error • that constitutes approximately 2% of all rejected images. • The consequence of double exposure can be either a single repeated examination, when an inanimate object is involved (Figure 11), or two repeated examinations when two patients are involved (Figure 12). • In DR, double exposures can also be caused by power interruptions and communications errors, as well as by inadequate erasure secondary to overexposure or erasure mechanism failure.

42. Double exposure (Figure 11),

43. Double exposure # 12

45. #8

46. Edge Enhancement • The secondary function of image processing is to customize contrast in the region of interest • This type of image processing includes modifying the image to enhance the contrast and sharpness of some features while compromising the contrast and sharpness of others, • as well as modifying the image to make it appear more like a conventional film. • This secondary image processing is applied in a manner that is usually specific to the anatomic projection.

47. standard image edge sharpening

48. Halo effect with Edge enhancement

50. Post Processing • An auxiliary purpose of image processing is to improve the usability of the digital image. • This includes imprinting demographic overlays, adding annotations, applying borders and shadow masks, flipping and rotating, increasing magnification, conjoining images for special examinations like scoliosis, and modifying the sequence of views. • This processing may require a separate QC workstation