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.

1. HRCT in Diffuse Lung Diseases - I
Dr. Bhavin Jankharia
Jankharia Imaging

2. Techniques and Principles

3. A Good Quality Study Is An
Absolute Must

4. HRCT
Technique
Most Important
In all cases
•Breath-hold
A good number of cases turn out to be like
this – blurred and then misinterpreted as
ground-glass attenuation

5. HRCT
Technique
Most Important
In all cases
•Breath-hold
In the same patient with good breath-hold,
you can now see some air-trapping, but no
interstitial lung disease

6. HRCT
Technique
Most Important
In 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. HRCT
Technique
Most Important
In all cases
•Breath-hold
•Full inspiration
The images were repeated a week or so later. The end-inspiratory images
show no significant abnormality

8. Insp Exp
This is another example of the problems that expiratory images can create in
interpretation

9. HRCT
Technique
Most Important
In all cases
•Breath-hold
•Full inspiration
This is what expiratory images look like in normal patients – a gradient of
increasing whiteness is seen from non-dependent to dependent – this is not
acceptable

10. HRCT
Technique
Most Important
In all cases
•Breath-hold
•Full inspiration
What we want is images like this – no gradient, pristine and clear blackness
in end-inspiration

11. There is another way to tell when
images are in expiration

12. Insp Exp
The trachea in expiration has a posterior convexity and this helps in picking
up expiratory images. Normally, in inspiration, the trachea should be round
or oval

13. HRCT
Technique
Most Important
In all cases
•Breath-hold
•Full inspiration
•Expiratory images

14. In most situations, except in the
follow-up of known interstitial lung
diseases, an expiratory set is also
required to assess the airways
and air-trapping

15. Insp Exp
The left lower lobe in expiration shows air-trapping, suggesting lobar
constrictive bronchiolitis

16. HRCT
Technique
Most Important
In all cases
•Breath-hold
•Full inspiration
•Expiratory images
•1mm or smaller slice
thickness

17. In 16-slice and higher scanners,
the current protocol is to do a
volume scan in 2-5 seconds and
then retrospectively reconstruct
the images as 1mm at 0.5mm
intervals and to review the stack
on the workstation

18. HRCT
Technique
Most Important Important
In all cases In selected cases
•Breath-hold •Prone images
•Full inspiration
•Expiratory images
•1mm or smaller slice
thickness

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. Supine Prone
This 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. Supine Prone
In this patient the dependent densities (arrow) in supine disappear in the prone
position – these are true gravity dependent densities and are of no significance

22. Practically, these are the most
important parameters to work with
when perfoming HRCT scans

23. To Repeat

24. HRCT
Technique
Most Important Important
In all cases In selected cases
•Breath-hold •Prone images
•Full inspiration
•Expiratory images
•1mm or smaller slice
thickness

25. HRCT
Technique
Other Parameters
These used to be discussed extensively in the era of conventional
scanners, 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. If providing films is still important,
then the filming should be done
such that the pleural margins and
ribs are seen with an optimum
grey-scale

27. Not acceptable

28. Correct window settings for filming

29. Please remember that the first
step in HRCT interpretation of
diffuse lung diseases is a good
quality scan

30. All possible efforts must be made
to obtain high quality scans. The
technologists, 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. Thank You