HRCT in Diffuse Lung Diseases - I (Techniques and Quality)

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The first part of a series on HRCT in diffuse lung diseases. This covers how to obtain good quality scans, which are the basis of learning how to interpret HRCT studies in the setting of diffuse lung diseases.

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HRCT in Diffuse Lung Diseases - I (Techniques and Quality)

  1. 1. HRCT in Diffuse Lung Diseases - I Dr. Bhavin Jankharia Jankharia Imaging
  2. 2. Techniques and Principles
  3. 3. A Good Quality Study Is An Absolute Must
  4. 4. HRCT TechniqueMost ImportantIn all cases•Breath-holdA good number of cases turn out to be likethis – blurred and then misinterpreted asground-glass attenuation
  5. 5. HRCT TechniqueMost ImportantIn all cases•Breath-holdIn the same patient with good breath-hold,you can now see some air-trapping, but nointerstitial lung disease
  6. 6. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspiration So often, the images are in expiration, leading to a spurious diagnosis of ground-glass attenuation as was made in this case
  7. 7. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspiration The images were repeated a week or so later. The end-inspiratory images show no significant abnormality
  8. 8. Insp ExpThis is another example of the problems that expiratory images can create in interpretation
  9. 9. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspiration This is what expiratory images look like in normal patients – a gradient ofincreasing whiteness is seen from non-dependent to dependent – this is not acceptable
  10. 10. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspirationWhat we want is images like this – no gradient, pristine and clear blackness in end-inspiration
  11. 11. There is another way to tell when images are in expiration
  12. 12. Insp ExpThe trachea in expiration has a posterior convexity and this helps in pickingup expiratory images. Normally, in inspiration, the trachea should be round or oval
  13. 13. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspiration•Expiratory images
  14. 14. In most situations, except in thefollow-up of known interstitial lungdiseases, an expiratory set is also required to assess the airways and air-trapping
  15. 15. Insp ExpThe left lower lobe in expiration shows air-trapping, suggesting lobar constrictive bronchiolitis
  16. 16. HRCT TechniqueMost ImportantIn all cases•Breath-hold•Full inspiration•Expiratory images•1mm or smaller slice thickness
  17. 17. In 16-slice and higher scanners, the current protocol is to do avolume scan in 2-5 seconds and then retrospectively reconstruct the images as 1mm at 0.5mmintervals and to review the stack on the workstation
  18. 18. HRCT TechniqueMost Important ImportantIn all cases In selected cases•Breath-hold •Prone images•Full inspiration•Expiratory images•1mm or smaller slice thickness
  19. 19. Prone images are required when there are reticular lesions or opacities only in the dependent portions and we need to differentiate between true interstitial lung disease and normal gravity-dependent densities
  20. 20. Supine ProneThis 30-years old lady with progressive systemic sclerosis came for an HRCT to rule out interstitial lung disease. Subtle disease (arrows) is seen in the supine and prone positions
  21. 21. Supine ProneIn this patient the dependent densities (arrow) in supine disappear in the proneposition – these are true gravity dependent densities and are of no significance
  22. 22. Practically, these are the mostimportant parameters to work with when perfoming HRCT scans
  23. 23. To Repeat
  24. 24. HRCT TechniqueMost Important ImportantIn all cases In selected cases•Breath-hold •Prone images•Full inspiration•Expiratory images•1mm or smaller slice thickness
  25. 25. HRCT TechniqueOther ParametersThese used to be discussed extensively in the era of conventionalscanners, but are not much relevant now•kV – use the lowest acceptable•mAs – use the lowest acceptable•Scan time – the fastest possible•FoV – irrelevant•Interslice gap – irrelevant•Filming – relevant only where films are still an important means of communication
  26. 26. If providing films is still important, then the filming should be donesuch that the pleural margins and ribs are seen with an optimum grey-scale
  27. 27. Not acceptable
  28. 28. Correct window settings for filming
  29. 29. Please remember that the firststep in HRCT interpretation ofdiffuse lung diseases is a good quality scan
  30. 30. All possible efforts must be made to obtain high quality scans. Thetechnologists, nurses, etc. should all be trained in making sure that they understand how to elicit proper breath-hold in end- inspiration, followed by an end- expiratory set as well
  31. 31. Thank You

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