2. INTRODUCTION
• CT based imaging is mostly now the FIRST- STEP in most centres for
evaluation of ACUTE STROKE.
• WIDE AVAILABILITY, SPEED AND SAFETY.
• NCCT HEAD is sufficient alone in decision-making for IV THROMBOLYSIS.
• It is recommended to proceed with CT ANGIOGRAPHY even before
measuring serum creatinine in patients eligible for MECHANICAL
THROMBECTOMY to avoid unnecessary delay in reperfusion of brain.
3. INTRODUCTION
• Primary modality to image blood vessels supplying brain and neck.
• From Aortic Arch to Vertex.
• NCCT and Clinical examination alone have limitations in detecting LVO.
• Therefore CTA is increasingly advocated as first line diagnostic test in ACUTE
STROKE with SENSITIVITY and SPECIFICITY upto approx. 98%.
• Takes 2 additional minutes.
• Radiation Exposure- 7-9 mSV
4. INDICATIONS OF CTA
• Arterial aneurysms or pseudo-aneurysms and venous varices.
• ISCHEMIC STROKE , vasospasm and thromboembolism.
• Intracranial haemorrhage and intraspinal haemorrhage.
• Vasculitis and collagen vascular diseases.
• ATHEROSCLEROTIC STENO-OCCLUSIVE DISEASE.
• Non-atherosclerotic, non-inflammatory vasculopathy.
5. • Traumatic vascular injuries
• Venous and dural sinus thrombosis (when performed as dedicated CTV)
• Vascular malformations and fistulas.
• Vascular anatomic variants.
• Evaluation for vascular intervention and follow-up (percutaneous and surgical)
• Tumours of vascular origin with rich vascular supply or involving vascular
structures.
24. TECHNIQUE
• PATIENT’S POSITION- supine with their arms by their side, hard palate
perpendicular to the table (chin down).
• SCOUT- mid-chest to vertex.
• SCAN EXTENT- aortic arch to vertex.
• SCAN DIRECTION- caudocranial, can be performed to minimise venous
contamination in the head portion of the scan, often utilised in slower
scanners.
• RESPIRATION PHASE- suspended.
25. • CONTRAST INJECTION CONSIDERATIONS- monitoring slice (region of
interest)-LEVEL OF C2.
• THRESHOLD- Manual trigger when contrast is seen within vertebral/ carotid
arteries.
• INJECTION- 18 -20 gm of NON-IONIC CONTRAST with a 50 ml SALINE
CHASER at 4.5-5 ml/sec.
• SCAN DELAY- minimal scan delay- wait for approx. 5 seconds before
contrast monitoring.
26. BONE SUBSTRACTION TECHNIQUES
• Commonly cited disadvantage of CTA- Difficulty in excluding BONE
ANATOMY.
• particularly, at the SKULL BASE
• To achieve ADEQUATE VISUALISATION OF THE LOCAL VASCULATURE.
27. IMAGE ACQUISITION
• Normal circulating time from injection of the contrast medium into the brain
averages 5-7 secs.
• 4 phases of CT ANGIOGRAM-
• 1- ARTERIAL PHASE- 1 - 2.5 secs. (EARLY ICA and LATE ICA)
• 2- CAPILLARY PHASE- 1 sec
• 3 and 4- VENOUS PHASE- 4-5 secs. (EARLY SUPERFICIAL and LATE
DEEP VEINS)
34. ADVANTAGES - SPEED
• MORE ADVANCED- 64, 128, 256 and 320 MDCT Scanner- SPEED and
RESOLUTION increased but radiation remained relatively same.
• Less breathing artefact.
• Less iodine dose.
35. RADIATION DOSE
• With MDCT- Overall radiation dose to patient does not significantly increase
for the image resolution achieved.
• About 2.5-3 mSV
36. ROLE OF CTA IN STROKE
• To DIAGNOSE and avoid misdiagnosis of VASCULAR OCCLUSION (Lacunar
infarct/ migraine/ TIA / Seizure).
• Detects THROMBUS- LOCATION, EXTENT and CHARACTER.
• COLLATERAL STATUS
• Assessment of ARTERIAL ANATOMY PRE-MT.
• Associated pathologies.
37. PRESENCE AND LOCATION OF
THROMBUS
• Identify Thrombus/ plaque in PROXIMAL LARGE ARTERIES.
• Identify LVOs in ICA, M1 ,M2 MCA (More proximal less likely to be
thrombolysed).
• Also TOP OF ICA SADDLE OCCLUSION- suggestive of poorer outcome and
less chance of thrombolysis.
• Identify CLOT BURDEN- PROGNOSTICATE and planning Management.
• Identify HIGH RISK TIAs- with proximal vessels.
38. CLOT BURDEN SCORE
• Assign 0-10.
• Determined by subtracting 2 if clot found in-
• SUPRACLINOID ICA
• PROXIMAL half MCA
• DISTAL half MCA trunk
39. • Score of 1 is subtracted when-
• INFRACLINOID ICA
• ACA
• Each M2.
• 10- NORMAL, LESSER THE SCORE HIGHER IS THE CLOT BURDEN.
42. NATURE OF THROMBUS
• Arterial Silhouette on CTA- IDENTIFY contrast permeation within intracranial
thrombus- RESIDUAL FLOW on CTA.
• GRADES-
• 0- No contrast permeation
• 1- Diffuse contrast permeation in thrombus
• 2- Tiny hairline lumen or streak of contrast extending through any length.
43.
44. • THORMBUS ATTENUATION INCREASE- mean thrombus HU (CTA)- mean
thrombus HU(NCCT).
• > 10 suggestive of- BETTER chance of THROBOLYSIS.
• Maximum thrombus attenuation of >90 HU- s/o PERMEABLE THROMBUS.
45. MULTIPHASE CT ANGIOGRAPHY
• In addition to identification of LVO, it can also identify patient’s COLLATERAL
CIRCULATION.
• Traditionally timed CTA images underestimate the collateral quality, as
intraarterial constrast do not arrive at these collateral circulation at the time of
image acquisition because of slower flow.
• To compensate this, MULTIPHASIC CTA images can be obtained.
46. • 70 cc contrast bolus (OMNIPAQUE 300 ) given at the rate of 4 ml/hr followed
by saline chaser.
• First phase (PEAK ARTERIAL PHASE) from AA to VERTEX.
• ROI in PROXIMAL DESCENDING AORTA and trigger value- 150 HU.
• Second phase( EQUILIBRIUM PHASE/PEAK VENOUS PHASE)- skull base to
vertex - 10 secs later.
47. • These multiple set of images allow ROBUST ASSESSMENT of COLLATERAL
CIRCULATION.
• Multiple SCORING SYSTEM have been used to quantify- typically on 4-5 scale.
• Scored either as GOOD or POOR collaterals.
• Poor collaterals predicts poor prognosis.
• ESCAPE TRIAL ( ENDOVASCULAR TREATMENT FOR SMALL CORE AND
ANTERIOR CIRCULATION PROXIMAL OCCLUSION) trial to aid in selection
of patients for MT.
48. IDENTIFICATION OF LARGE VESSEL
OCCLUSION
• The images obtained by CTA capture contrast in the lumen of the extra cranial
and intracranial vasculature
• Can be combined to create 2-D maximal-intensity projections and 3-D
reconstructions.
• An intraluminal thrombus will appear as a lack of contrast opacification in a
given vessel segment, creating a filling defect.
• Due to its easy availability, efficiency and accuracy- standard non-invasive test
for identifying LVO.
49.
50. • Ischemic Brain with minimal OR No
vessels.
• Ischemic brain with one phase
delay in contrast filling with impaired
washout in THIRD PHASE.
• ONE PHASE delay in filling with
washout in THIRD PHASE.
• IRREVERSIBLE BRAIN INJURY
• SEVERLEY ISCHEMIC BRAIN
• MILDLY ISCHEMIC BRAIN
51. CT PERFUSION
• Like CTA, CT PERFUSION (CTP) imaging is done by acquiring multiple scans
over time following iv administration of iodinated contrast.
• Radiation exposure is higher as compared to CTA.
• The series of images follows the contrast material as it arrives the brain tissue
and washes out through the venous system.
• With this information, the scanner then determines ESTIMATES OF
CEREBRAL BLOOD FLOW, CEREBRAL BLOOD VOLUME and MEAN
TRANSIT TIME.
• Using this it can be determined whether brain tissue is NORMALLY
PERFUSED, ISCHEMIC or INFARCTED.
52. • POST-PROCESSING of CTP images creates maps to approximate the SIZE
and LOACTION of infarct core and ISCHEMIC PENUMBRA
• IDENTIFICATION OF MISMATCH BETWEEN SIZE OF CORE INFARCT and
SIZE OF ISCHEMIC PENUMBRA suggests reversibility of ischemic with timely
REPERFUSION and therefore used to select patients for MECHANICAL
THROMBECTOMY beyond 6 hours.
• Patient specific “TISSUE-CLOCK” as opposed to time based (6 hours from
stroke onset)- AHA/ASA guidelines.
• In various studies done, no outcome difference was noted in EARLY STROKE
based on imaging modality selection
59. • CTA reveals focal areas of
increased enhancement
suggestive of arteriovenous
malformation adjacent to Right
occipital horn, which was
determined as a source of
haemorrhage.
60. • CT reconstruction AP OBLIQUE
VIEW shows arteriovenous
malformation nidus (large arrow)
with right posterior cerebral
artery (small arrows) as a
ARTERIAL FEEDING SUPPLY
and prominent draining vein
(small arrows) draining into
internal cerebral vein (large
arrow).
61. POST-PROCESSING
• CTA images are usually presented as AXIAL and CORONAL and/or
SAGGITAL MULTIPLANAR REFORMAT OF A VARIETY OF THICKNESS.
• Additional post-processing techniques include-
• MIP (MAXIMUM INTENSITY PROJECTION)- displays pixels with higher CT
value.
• CURVED PLANAR REFORMATS- delineates the entire course of vessel and
can be used when the vessel is tortuous.
• SHADED SURFACE DISPLAY VOLUME RENDERING (SS- VRT)- displayed
as 3D. Used for pre-operative planning.
62. CTA- ADVANTAGES
• Widespread availability and accessibility of multidetector CT SCANNERS.
• Simple protocols (out-patient basis)
• 3D imaging data set.
• Rapid screening (even in non-complaint patients)-FAST IMAGE
ACQUISITION.
• Ability to visualise calcium.
• Lower cost as compared to MRA.
63. • Additionally, CTA allows multiplanar reconstruction and better appreciation of
PLAQUE CHARACTERISTICS and MORPHOLOGY.
64. CTA- DISADVANTAGES
• Radiation exposure.
• Potentially nephrotoxic contrast agents.
• Reduced accuracy in calcified segments.
• LOWER RESOLUTION than CATHETER angiography, making the
assessment of SUBTLE WALL CHANGES , such as those with DISSECTION
or VASCULITIS more difficult to identify.
65. ADVANTAGES OF MRA OVER CTA
• Less radiation exposure
• Can be performed without contrast.
• Better tissue-characterisation.
• Better visualisation of brain parenchyma.
• Plaques In the vessels with or without calcium can be quantified as- NONE,
MILD,MODERATE and SEVERE.
