Imaging in acute stroke

Dr Samuel Gregson Radiology SpR

Radiologist?? This is a clinical diagnosis!

CT vs MRI in hyperacute stroke

- Fast acquisition (seconds vs minutes)

- Availability - Multiple scanners

- Resolution / artefacts

- Cost

- Radiation dose

CT Head: Non contrast

Unenhanced CT Head

First imaging modality used in acute stroke

Fast less than 10 seconds

Volume acquisition 1mm slices allows formatting in all planes

Infarct vs Bleed

Infarcts

Wedge shaped

Involve grey white matter junction

Loss of sulci

Anatomical to vascular distribution

Low attenuation indicated cytotoxic oedema

Haemorrhagic stroke

Most commonly secondary to hypertension

Classic anatomical areas:

Putamen, Thalamus, Pons, Cerebellum

High attenuation change with thin rim of surrounding

Oedema

Stroke mimics

Glioblastoma Mucinous metastases

Unenhanced CT

The hyperacute signs - only identified 15-60% of patients

Territories of infarct

Territories of infarct

Territories of infarct

Complications of infarct

CT Angiography (CTA)

CTA: Intracranial CT angiogram

Use of intravenous contrast to fill the intracranial arterial

vessels

May identify the thrombus within a vessel which may

guide intra-arterial thrombolysis or clot retrieval

Also evaluates the carotid and vertebral arteries of the

neck to establish the aetiology of stroke i.e.

atherosclerosis or dissection

Provides a vascular map for intervention

Left MCA M1 Branch Occlusion

Basilar tip thrombus

Vertebral artery dissection

Presented with neck pain following trauma

Vertigo, right sided hearing loss, nystagmus

Assessing carotid stenosis

Using curved planar reformats focal plaque

stenoses can be measured

CT perfusion

Becoming more established in most acute stroke centres with intervention

Important adjunct along side CT intracranial angiopathy

Differentiation of salvageable ischaemic brain tissue (penumbra) from irrevocably

infarcted brain (infarct core) - vital in assessment for thrombolysis / clot retrieval

CT perfusion

Patient with small core and large penumbra is most likely to benefit from

reperfusion therapies

Three parameters used:

1. Mean transit time (MTT) or time to peak (TTP) of deconvolved tissue residue

function (Tmax)

2. Cerebral blood flow (CBF)

3. Cerebral blood volume (CBV)

CT perfusion

Ischaemic core:

Increase mean transit time

Markedly decreased CBF

Markedly decreased CBV

CT Perfusion

Penumbra

Increased mean transit time

Moderately reduced CBF

Near normal or increased CBV

Right MCA infarct with good penumbra

MR Imaging

MRI Basic sequences

MRI Diffusion weighted sequences

Measures random Brownian motion of water molecules within a voxel of tissue

I.E. how water molecules are able to diffuse

Acute infarct - Restricted diffusion

Evolution of stroke on MRI

CT vs MRI Diffusion

Future advances?

Vascular wall imaging 3T MRI

Atherosclerosis Vasculitis

Imaging in stroke...

Vital in the early management of acute infarction

Confirms diagnosis and ensures no contraindications to treatment

Gives objective picture of infarction and possible salvageable penumbra

Aiding neurovascular intervention

Thanks! Questions?