ct_imaging_2019_lyl_v01_2 ct_imaging_2019_lyl_v01_2 (1).pptxct_imaging_2019_lyl_v01_2 (1).pptx(1).pptx
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The document is a comprehensive guide on the use of CT imaging for making treatment decisions in stroke cases, focusing on Hounsfield units (HU) for differentiating between various tissue types and conditions. It outlines techniques for identifying ischaemic damage, assessing stroke severity, and ruling out bleeding, as well as practical tips on using the e-aspects software to enhance the accuracy of image interpretation. Emphasis is placed on standardized procedures for evaluating scans to improve diagnostic sensitivity and specificity.
ct_imaging_2019_lyl_v01_2 ct_imaging_2019_lyl_v01_2 (1).pptxct_imaging_2019_lyl_v01_2 (1).pptx(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