ct_imaging_2019_lyl_v01_2 (1).pptxct_imaging_2019_lyl_v01_2 (1).pptxct_imaging_2019_lyl_v01_2 (1).pptxct_imaging_2019_lyl_v01_2 (1).pptx

1. CT imaging for making treatment decisions
Presenters Name
Date

2. CT imaging - recap
X-ray attenuation of any given tissue
type is relatively constant
Attenuation coefficient is measured in
Hounsfield Units (HU)
Viewing software converts a range of
HU values to shades of grey

3. CT imaging - recap
The range of HU values is defined by
the level (centre) and window (width)
Different ranges are commonly used
for different body parts
Common ranges are also often referred
to as windows e.g. “bone window” or
“lung window”
Note: All images in this presentation have a level of 40 HU and window of 80 HU unless otherwise stated
BRAIN
L40 W80
BONE
L750
W3500
HIGH
CONTRAST
L32 W20

4. CSF 8
TISSUE TYPICAL HU VALUE
WHITE MATTER 30
GREY MATTER 45
FRESH BLOOD 60
CALCIFICATIONS 100+
BONE 1000+
CT imaging - recap
When looking for a clot (Hyper dense artery sign) > 45 HU
Calcifications > 100 HU

5. CT acquisition coverage
CORRECT INCORRECT

6. CT acquisition coverage → result
CORRECT INCORRECT

7. CT acquisition coverage → consequences
MISSED BLEED

8. Quality of the acquisition
CORRECT INCORRECT

9. Keep a level head
We need to be able to compare similar
structures in both hemispheres to
identify ischaemic damage
If the patient’s head is not in line with
the scanner, the scan may be hard to
interpret
If the patient cannot hold their head
straight, use the CT scanner software or
e-ASPECTS to straighten the image after
acquisition
BAD
GOOD
Identify early ischaemic damage

10. Side alignment of the scan

11. Scanner artefacts
Identify early ischaemic damage
METAL
OBJECT
Metal objects reflect X-rays and cause
bright and dark lines on the scan
Movement during acquisition may
result in a blurred image or cause
discontinuities between slices
Images can be noisy (grainy),
particularly when viewing thin slices

12. CONSIDER HOUNSFIELD UNITS
(HU’s)
SET THE CORRECT WINDOWING
(Windowing)
KNOW WHAT YOU ARE LOOKING
FOR AND WHERE TO FIND IT
(Scrolling)
3 ways to improve image interpretation

13. ASSESS STROKE SEVERITY
EXCLUDE BLEEDING

14. 1. Bleeds are much easier to see in Brain window than Ischemia window
BRAIN WINDOW ISCHEMIA WINDOW
WINDOWING SCROLLING CONSIDER HU

16. 2. Look for signs of bleeding
To make sure you cover the whole
brain, divide the image into 4 quadrants
Scroll through the image, analysing
each quadrant and looking for bleeding
WINDOWING SCROLLING CONSIDER HU

18. Intra-cerebral haemorrhage
This scan shows an intra-cerebral
haemorrhage (ICH)
The “bright” area measures 60-70 HU
Blood was visible on other slices
covering >40 mm axially
WINDOWING SCROLLING CONSIDER HU

19. Intra-cerebral haemorrhage
This scan shows a much smaller ICH
This haemorrhage was visible on other
slices covering ≈20 mm axially
WINDOWING SCROLLING CONSIDER HU

20. Sub-arachnoid haemorrhage
This scan shows a sub-arachnoid
haemorrhage (SAH)
SAHs can be less obvious than ICHs due
to their location within the
subarachnoid space, especially when
close to the skull
Beam-hardening artefacts can further
obscure blood, especially in the
posterior fossa
WINDOWING SCROLLING CONSIDER HU

21. 3. Use Hounsfield units to differentiate
WINDOWING SCROLLING CONSIDER HU
CSF 8
TISSUE TYPICAL HU VALUE
WHITE MATTER 30
GREY MATTER 45
FRESH BLOOD 60
CALCIFICATIONS 100+
BONE 1000+
When looking for a clot (Hyper dense artery sign) > 45 HU
Blood > 60 HU < 100 HU
Calcifications > 100 HU

22. Use Hounsfield Units to distinguish between Blood and Calcifications
BRAIN WINDOW ISCHEMIA WINDOW
WINDOWING SCROLLING CONSIDER HU

23. Intra-cerebral haemorrhage
WINDOWING SCROLLING CONSIDER HU
MAX 70 HU
(BLOOD)
MAX
102 HU
(CALCIFICATION)
MAX
298 HU
(CALCIFICATION)
Blood in CSF should not be confused
with calcifications, which are often
present in the ventricles
Use your viewer’s measurement tools
to check HU values
Beware of partial volume effects
causing edges to reduce in HU value

24. ASSESS STROKE SEVERITY
EXCLUDE BLEEDING

25. 1. Ischemia is much easier to see in Ischemia window than Brain window
BRAIN WINDOW ISCHEMIA WINDOW
WINDOWING SCROLLING CONSIDER HU

26. Hypodensity using Ischemic window
WINDOWING SCROLLING CONSIDER HU
Hypodensity can be made more visible by reducing the window width to increase contrast
This image uses a window centred on 32 HU, with a width of 20 HU

27. 2. Cerebral vascular territories
Note: we are not considering strokes in ACA or PCA territories
Look for signs of established Hypodensity in the
MCA region
As ischaemia develops, both white and grey
matter will begin to appear hypodense (darker)
and continue to darken over time
Hypodensity indicates ischaemic core with
irreversible damage
WINDOWING SCROLLING CONSIDER HU
ACA
PCA
MCA
MCA
ACA – ANTERIOR CEREBRAL ARTERY
TERRITORIES
MCA – MIDDLE CEREBRAL ARTERY
PCA – POSTERIOR CEREBRAL ARTERY

28. >1/3 MCA - Its probably not 2 hours since onset
JAMA. 2001;286(22):2830.
Only around 30% of stroke patients will
have signs of early ischemic damage in
the first 3 hours after symptom onset.
Established hypo density of > 1/3 of the
MCA region indicates that the stroke
symptoms has probably started > 3
hours ago.
WINDOWING SCROLLING CONSIDER HU

29. 3. Using Hounsfield units can help
CSF 8
TISSUE TYPICAL HU VALUE
WHITE MATTER 30
GREY MATTER 45
FRESH BLOOD 60
CALCIFICATIONS 100+
BONE 1000+
Brain tissue has a HU of < 45 HU
Hypodense tissue has lower HU
WINDOWING SCROLLING CONSIDER HU

30. Hypodense tissue has a lower HU
WINDOWING SCROLLING CONSIDER HU
Area of ischemia 25 HU
Surrounding area 36 HU

31. CT interpretation to guide treatment decisions (Recap)
CONSIDER HOUNSFIELD UNITS
(HU’s)
SET THE CORRECT
WINDOWING
(Windowing)
KNOW WHAT YOU ARE
LOOKING FOR AND WHERE TO
FIND IT (Scrolling)
1. EXCLUDE
BLEEDING
2. SEVERITY /
TIME

32. Tumours & abscesses
ASSOCIATED OEDEMA IS FINGER-SHAPED
STROKE DAMAGE USUALLY APPEARS TO BE
WEDGE-SHAPED, RADIATING AWAY FROM
THE OCCLUSION
TUMOURS APPEAR AS ILL-DEFINED REGIONS OF EITHER
HYPO- OR HYPERDENSITY
ABSCESSES APPEAR SIMILAR TO TUMOURS
ON CT
PATIENTS WITH THESE CONDITIONS SHOULD NOT BE GIVEN THROMBOLYSIS DUE TO THE RISK OF BLEEDING

33. Cerebral atrophy
Identify early ischaemic damage
In older patients, it is common to see
evidence of cerebral atrophy
“Shrinking” of the brain causes the
ventricles and sulci to become larger
Can make it more difficult to identify
structures

34. Old damage
Identify early ischaemic damage
Patients who have previously had
strokes may show long-standing
hypodensities
Tissue below ≈25 HU is likely to be old
damage
It may be difficult to compare
structures if opposite side is damaged
New damage may be hidden within the
older damage

35. This is all you need to make treatment decisions in acute stroke
CONSIDER HOUNSFIELD UNITS
(HU’s)
SET THE CORRECT
WINDOWING
(Windowing)
KNOW WHAT YOU ARE
LOOKING FOR AND WHERE TO
FIND IT (Scrolling)
1. EXCLUDE
BLEEDING /
CONTRAINDICAT
IONS
2. SEVERITY /
TIME

36. But we want you to be very confident in your interpretation

37. With
or
Without
The Angels WOW Study
Improving CT Scan interpretation by using the e-Aspects software

38. The problem with learning how to read a CT scan
Its like learning to play golf in the dark.
It might feel like a good shot but you don’t really know if it
when straight or in the wrong direction. Which means the
small adjustments necessary to grow is not possible.
Reading a CT scan is the same, unless you do a follow up MRI
you never really know where you where 100% right and
what you missed.
The Angels WOW study is like a golf simulator.
By utilizing the e-Aspects software as a training tool you
will to learn to implement a standardized process and
grow by seeing the result.

39. The WOW study has been proven to increase sensitivity and specificity
of identifying early signs of ischemic damage by as much as 50%

40. How the Angels WOW study will work
Every user registers and logs in using their own credentials.
Everyone scores the first 10 cases on the online tool to
establish their baseline.
After that , participants receive training on how to identify
signs of ischemic damage using a standardized process.
To practice using the steps all users will now have the
opportunity to score 60 scans that will be presented
randomly with or without the e-Aspects interpretation.
After practicing with the 60 WOW scans each participant will
use the same tool to score the first 10 cases again (in a
different order) to see if their skill level has improved.
10 cases (without)
Training
60 Cases WOW
10 cases (without)

41. Cerebral vascular territories - superior lateral ventricle level
Note: we are not considering strokes in ACA or PCA territories
ACA
PCA
MCA
MCA
ACA – ANTERIOR CEREBRAL ARTERY
TERRITORIES
MCA – MIDDLE CEREBRAL ARTERY
PCA – POSTERIOR CEREBRAL ARTERY

42. ASPECTS regions
Quantify damage using ASPECTS
M1
M2
M3
L
I
C
IC
SEVEN AT THE LEVEL OF THE BASAL GANGLIA
C - HEAD OF CAUDATE NUCLEUS
I - INSULA
IC - INTERNAL CAPSULE
ASPECTS DIVIDES THE MCA-SUPPLIED CEREBRAL TERRITORIES
INTO TEN REGIONS
L - LENTIFORM NUCLEUS
(PUTAMEN + GLOBUS PALLIDUS)
CORTICAL REGIONS M1, M2 AND M3

43. ASPECTS regions
Quantify damage using ASPECTS
M4
M5
M6
THREE ABOVE THE LEVEL OF THE
BASAL GANGLIA
CORTICAL REGIONS M4, M5 AND M6

44. The WOW Tool - Start with the first 10 cases

45. HYPERDENSE ARTERY SIGN
INTERNAL CAPSULE
BASAL GANGLIA
INSULAR RIBBON
IDENTIFY SIGNS OF EARLY
ISCHAEMIC DAMAGE

46. The vast majority of strokes are in the MCA region so it could make
sense to start a standardised procedure by looking there first
1. J Clin Neurol. 2013 Apr; 9(2): 97–102.
ACA
PCA
MCA
MCA
68%
24%
8%
Stroke distribution1
MCA PCA ACA

47. What do CT scans have in common with Frogs and Boomerangs?

48. Step 1. Hyperdense artery sign
HYPERDENSE ARTERY SIGN
Thrombus within the MCA vessel
100% sensitivity
Only 30% specificity as calcification,
blood flow and haematocrit can affect
appearance
Unaffected side must appear normal
Expect density of >43 HU

49. Step 1. Hyperdense artery sign
Scroll down until you find the frog
The Mid Cerebral Artery (MCA) is represented by the arms of the frog

50. 3. Use Hounsfield units to differentiate
CSF 8
TISSUE TYPICAL HU VALUE
WHITE MATTER 30
GREY MATTER 45
FRESH BLOOD 60
CALCIFICATIONS 100+
BONE 1000+
When looking for a clot (Hyper dense artery sign) > 45 HU
WINDOWING SCROLLING CONSIDER HU

51. Hyperdense artery sign
HYPERDENSE ARTERY SIGN
Hyperdense MCA
measures around 50 HU
in this scan
Surrounding tissue is
around 30 HU

52. Hyperdense artery sign
HYPERDENSE ARTERY SIGN
This example is more subtle
The hyperdense part is around 45 HU

53. The relevance of a Hyperdense artery
IVT has a very low potential to
recanalize occluded vessels if
thrombus length exceeds 8 mm
It gives a clue that Mechanical
Thrombectomy could be indicated.
The position of the clot should be
confirmed with CT Angio
Stroke. 2011;42:1775–1777

54. Identifying signs of early ischemic damage
- direction of process
INTERNAL CAPSULE
BASAL GANGLIA
INSULAR RIBBON
Look for loss of grey/white differentiation

55. There should be a clear boundary between the grey and white matter
Find the same structure on both sides of the brain
If one side is damaged then it will be less clearly delineated than its opposite
Consider the insular ribbons below
Checking grey/white differentiation
DAMAGED
INSULA
HEALTHY
INSULA

56. It can be difficult to see the differences when using a standard
level and window in your viewer
Reducing the window width will increase contrast and make the comparison easier
This image uses a level of 32 HU and window of 20 HU
Checking grey/white differentiation
DAMAGED
INSULA
HEALTHY
INSULA

57. We can also see a loss of grey/white matter
differentiation affecting the cerebral cortex on the
outside of the Sylvian fissure in this example
Checking grey/white differentiation
DAMAGED
CORTEX
HEALTHY
CORTEX

58. From the Frog, Scroll up until you find
slices showing the insular ribbon
It appears as a thin line of grey matter
next to a darker grey subcortical area
(white matter)
Follow a standardised “Step-wise” approach

59. Internal capsule
Once you can see the Insular ribbon scroll up or down one or two slices until you
can see a clear Internal capsule on the “Healthy Side”
The Internal capsule is visible as a curved dark line that looks like a Boomerang
INTERNAL CAPSULE

60. If there is damage in the Internal
capsule there will be a less well defined
“Boomerang” on the affected side
compared to the “Healthy side”
Internal capsule
INTERNAL CAPSULE

61. From the Internal capsule you now
move outwards
The Basal ganglia situated between the
internal capsule and the insular ribbon
Basal ganglia
BASAL GANGLIA

62. The insular ribbon is often one of the
first structures to be affected
When grey/white differentiation is lost,
the insular ribbon itself is lost
The insular cortex is more susceptible to
ischemia following MCA occlusion than
other portions of the MCA territory
because it has the least potential for
collateral supply from the anterior
cerebral and posterior cerebral arteries
Insular ribbon sign
INSULAR RIBBON

63. Once you are done with analysing the MCA region you could now focus
on finding ischemic signs in the PCA and ACA regions
1. J Clin Neurol. 2013 Apr; 9(2): 97–102.
ACA
PCA
MCA
MCA
68%
24%
8%
Stroke distribution1
MCA PCA ACA

64. Swelling
SWELLING MAY BE PART OF BOTH THE ISCHAEMIC CORE AND PENUMBRA,
SO DAMAGE MAY BE REVERSIBLE
SWELLING MAY APPEAR IN SEVERAL DIFFERENT WAYS
COMPRESSED VENTRICLES
EFFACED SULCI
MID-LINE SHIFT
SWELLING GENERALLY TAKES SOME TIME TO DEVELOP SO IT IS OFTEN NOT VISIBLE DURING
THE EARLY TIME WINDOW FOR THROMBOLYSIS
IF THERE IS SIGNIFICANT, VISIBLE SWELLING, THE PATIENT MAY BE AT INCREASED RISK
OF HAEMORRHAGE FOLLOWING THROMBOLYSIS
SWELLING
(SULCI / MIDLINE SHIFT)

65. Swelling - compressed ventricles
THE LEFT ANTERIOR HORN OF THE LATERAL VENTRICLE
IS COMPRESSED COMPARED TO THE RIGHT
IN THIS SCAN
BEWARE
A TILTED SCAN CAN MAKE VENTRICLES APPEAR TO BE
SMALLER ON ONE SIDE
THERE IS ALSO EXTENSIVE HYPODENSITY
AND LOSS OF GREY/WHITE MATTER
DIFFERENTIATION
HYPODENSE
TISSUE
SWELLING

66. Swelling - effaced sulci
WHEN SWOLLEN, SULCI ON ONE SIDE WILL APPEAR
SMALLER AND LESS WELL DEFINED
SULCI IN THE CEREBRAL CORTEX SHOULD APPEAR
ROUGHLY SYMMETRICAL
IN A HEALTHY BRAIN
ESPECIALLY WHEN COMBINED WITH A LOSS OF
GREY/WHITE MATTER DIFFERENTIATION
SWELLING
(SULCI / MIDLINE SHIFT)

67. Swelling - effaced sulci
Ensure the scan is level
so you can compare
similar sulci
Scroll up and down
through slices to check
the appearance of sulci
as they change
direction
Beware - partial
volume effects can
cause blurring of sulci
HEALTHY
SULCI
EFFACED
SULCI
SWELLING
(SULCI / MIDLINE SHIFT)

68. Swelling - mid-line shift
Mid-line shift rarely
occurs within 4 hours
of stroke onset (age
dependent)
Below is a comparison
of the same patient
within 4 hours of
onset (left) and over
24 hours later (right)
NO LONGER
ON THE
MID-LINE
SWELLING
(SULCI / MIDLINE SHIFT)

69. Scroll down to Find the frog. Look to find the
Hyperdense artery (HU>45)
Scroll to the Insula ribbon. Once you find it scroll up
or down to find the Boomerang (Internal Capsule).
Work your way outwards from the Internal Capsule
to the Basal Ganglia.
Next is the Insular Ribbon.
After this you could analyze the PCA and ACA regions.
Swelling is normally found in patients with advanced
ischemia.
HYPERDENSE ARTERY SIGN
INTERNAL CAPSULE
BASAL GANGLIA
INSULAR RIBBON
SWELLING
(SULCI / MIDLINE SHIFT)
IDENTIFY SIGNS OF EARLY
ISCHAEMIC DAMAGE

70. Lets try and apply these steps on some example cases
HYPERDENSE ARTERY SIGN
INTERNAL CAPSULE
BASAL GANGLIA
INSULAR RIBBON
SWELLING
(SULCI / MIDLINE SHIFT)

71. The WOW Tool - Now practice using these steps on the
60 WOW cases