This document discusses the use of multi-modality imaging in evaluating ischemic stroke. It compares CT and MRI for 5 objectives: 1) excluding hemorrhage, 2) eliminating other diagnoses, 3) detecting the infarct core, 4) evaluating salvageable tissue, and 5) assessing intracranial circulation. MRI is generally superior to CT for objectives 2-4 due to its increased sensitivity, while CT is comparable or better for objectives 1 and 5 due to its wider availability and faster scan times. The optimal imaging approach depends on the specific situation and capabilities of the facility.

1. Ischemic Stoke
Multi-modality imaging, daily exploration
Pr Jean-Pierre PRUVO
CHU Lille - France
1st Italian-French Update Imaging – IFUPI
Advanced Multiparametric Imaging - How to use in daily practice
MILAN March 23-24 2018
www.jfim.org

2. What are the objectives of both
imaging modalities ?
1. To exclude hemorrhage
2. To eliminate another diagnosis
3. To detect the infarct core
4. To evaluate the salvageable tissue (penumbra)
5. To assess the intracranial circulation
Treatment at the acute phase ?

3. 1. To exclude hemorrhage
T2*FLAIRT1
MRICT
Non contrast CT

4. CT MRI
Hemorrhage + +
Sensitivity of MRI is equivalent to CT
for detecting hyperacute hemorrhage
COMPARISON CT vs MRI

5. 2. To eliminate another diagnosis
Stroke mimics ?
Mme R…44-year-old. No medical history. No cardio vascular risk factor.
Admitted in emergency for an acute right hemiparesis at H4.
b1000 ADC FLAIR

6. 2. To eliminate another diagnosis
Stroke mimics ?
T1-Gd FLAIR
T2 SE
Multiple sclerosis

7. Stroke mimics ?
Mr T…65-year-old. Hyperlipemia, hypertension. Headaches for several days.
Admitted at H6 for seizure and right hemiparesis. MRI as first examination
b1000
ADC
FLAIR
T1-Gd
Oligodendroglioma
2. To eliminate another diagnosis

8. CT MRI
Hemorrhage + +
Stroke mimics + ++
In more than 20% of cases, the final diagnosis is not a stroke
MRI is much more sensitive than CT to diagnose stroke mimics
COMPARISON CT vs MRI

9. 3. To detect the infarct core
Diffusion : microscopic motions of water molecules
Decreased O2 supply
Na/K pump failure
Redistribution of water
Cytotoxic edema
MRI : diffusion imaging

10. Acute cerebral infarct : MRI
Hypersignal on diffusion – Decreased ADC
Sensitivity and specificity > 90% for detecting infarct core *
Excellent intra and inter-observer reproducibility * *
Right deficit < 3 hours
FLAIR b 1000 ADC

11. ŒAcute cerebral infarct : non contrast CT
Intravascular anomalies
High density values of the thrombus
(hyperdense vessel sign)
Parenchyma anomalies
Contrast attenuation
Mass effect
Insular ribbon
Cortical sulcus
Ventricular system
Lateral fissure, cortical sulcus
Lentiform nucleus
Sensitivity 30 – 40 %
Sensitivity 45 – 60 %

12. Acute cerebral infarct : CT perfusion
• 40 ml CM 350 / 400 mg Iodine, 5 ml/sec, 40 ml saline flush
• 64 sections, 5-mm thickness, 40-mm coverage, 80 kV – 100 mA
• Cine mode (1sec for 45 sec)
UH
T
MTT
CBV
CBF = CBV/MTT
TTP
MTT
CBV
CBF
Infarct core = CBV < 2ml/100g or < 60%

13. COMPARISON CT vs MRI
Mme M…68-year-old. Hyperlipemia. Sudden aphasia and right hemiparesis.
CT perfusion and diffusion MR imaging performed immediatly at H3
MTT
CBV
DWI
CT perfusion

14. DWI
CBV
MTT
Me O…52-year-old. Acute left hemiplegia at H4
COMPARISON CT vs MRI
CT perfusion

15. DWI
CBV
MTT
Mr S…76-year-old. Acute right hemiparesis at H2
COMPARISON CT vs MRI
CT perfusion

16. DWI
CBV
MTT
Mr O…68-year-old. Sudden headaches, dysarthria, right hemiparesis
COMPARISON CT vs MRI
CT perfusion

17. CT MRI
Hemorrhage + +
Stroke mimics + ++
Infarct core + ++
Posterior fossa - ++
Lacunar infarct - ++
Diffusion is the gold standard for detecting acute infarction.
Limitations of CT include: infarcts in the posterior fossa, small
cortical infarcts and lacunar infarcts.
COMPARISON CT vs MRI

18. 4. To evaluate the salvageable tissue
CT and MR perfusion techniques
CT MR
Gd bolus injection → susceptibility effect →
local gradients → spin dephasing → signal
attenuation
Iodine-based contrast bolus injection →
increased then decreased density of brain
parenchyma over time
Linear relationship between contrast
concentrations and image density
Lack of linearity between signal intensity
and concentration of contrast media
Absolute quantification Unreliable quantification
TTM TTM

19. 4. To evaluate the salvageable tissue
MTT MTTDiffusion CBV
MR
Mismatch
Diffusion / Perfusion
CT
Normal CBV
Abnormal MTT (> 145%)

20. CT MRI
Hemorrhage + +
Stroke mimics + ++
Infarct core + ++
Posterior fossa - ++
Lacunar infarct - ++
Salvageable tissue + +
MR: the clinical utility of mismatch remains controversed
CT : lack of consensus for infarct core/penumbra thresholds
COMPARISON CT vs MRI

21. 5. To assess the intracranial circulation
CT angiography (80 ml Iodine 350 / 400 mg, 4-5 ml/ sec)
Sensitivity and specificity of CTA > 90% for detecting proximal vessel occlusion
CTA is an accurate method to evaluate distal vessels and collateral circulation

22. 5. To assess the intracranial circulation
MR angiography (3D TOF or CE MRA)
3D TOF : signal-intensity drop-out or flow void by intravoxel dephasing
CE-MRA : limited spatial resolution, vein overlap after perfusion MR
3D TOF
CE MRA

23. CT MRI
Hemorrhage + +
Stroke mimics + ++
Infarct core + ++
Posterior fossa - ++
Lacunar infarct - ++
Salvageable tissue + +
Intracranial vessels ++ +
COMPARISON CT vs MRI
CTA is more accurate than MRA for evaluating intracranial circulation

24. CT MRI
Availibility Yes Variable
Scan time Fast 10 min
Imaging coverage Limited Whole brain
Artifacts Rare Frequent
Radiation exposure 12 mSev No
Contraindications Rare Frequent
PRACTICAL CONSIDERATIONS
CT : more available, faster with less contraindications

25. CT MRI
Hemorrhage + +
Stroke mimics + ++
Infarct core + ++
Posterior fossa - ++
Lacunar infarct - ++
Salvageable tissue + +
Intracranial vessels ++ +
Practical considerations ++ +
COMPARISON CT vs MRI

26. MRI / CT ?
MRI available
in emergency
MRI not available
Contraindication
Diffusion
Perfusion
CTA
Perfusion
CTMR
MRA