Beyond Conventional Treatment Time Window: Acute Stroke Treatment with Artificial Intelligence (AI)-assisted Intra-arterial Thrombectomy

Dr. LI Chung Ki, Patrick

Co-Director, Neurology Centre

Honorary Consultant in Neurology

Specialist in Neurology

Dr. LO GOH, Gladys

Head, Department of Diagnostic and

Interventional Radiology

Honorary Consultant in Radiology (Diagnostic)

Dr. TSOI Tak Hong

Co-Director, Neurology Centre

Honorary Consultant in Neurology

Specialist in Neurology

Dr. NG Ping Wing

Honorary Consultant in Neurology Specialist in Neurology

Dr. AU YEUNG Kai Ming, Paul

Honorary Consultant in Radiology (Diagnostic)

Specialist in Radiology

Dr. LEUNG Kar Ming

Honorary Consultant in Neurosurgery

Specialist in Neurosurgery

Globally, 1 out of every 4 people suffers from stroke, which causes a death every 6 seconds. Stroke is also a major cause of permanent disability in adults in Hong Kong, leading to about 3,000 deaths annually. 

There are 2 types of acute stroke, i.e. hameorrhagic stroke and ischaemic stroke. The former happens when a blood vessel bursts and bleeds into the brain, while the latter occurs when the brain is deprived of blood supply by blood vessel blockage. Clinical examination and brain scan are required for diagnosis of both types of stroke.

Signs of Haemorrhagic Stroke

• Severe headache
• Delirium, coma

Signs of Ischaemic Stroke

• Slurred speech
• Half facial paralysis
• Paralysis or weakness on one side of the body

Ischaemic stroke is caused by blood clots cutting off oxygen and nutrient supply to brain tissues with long-term, adverse impact on bodily functions. Therefore, the earlier the therapeutic interventions, the better the clinical outcome.

 “Time is Brain”

For patients with ischaemic stroke, stroke-induced disability can be mininised. If they are sent to the hospital for clinical assessment and intravenous thrombolytic therapy to restore blood flow to the brain within 3 hours after onset.

Research suggests that, while improvement is noted in some patients with treatment over 4.5 hours after onset, the risk of cerebrovascular complications increases with the time lapsed after onset. Intravenous thrombolytic therapy is also found to be less effective for stroke caused by large vessel occlusion. 

Go beyond the Golden Treatment Time Window with AI-assisted Intra-arterial Thrombectomy

Thanks to technological advance, intra-arterial thrombectomy can now be a lifeline to severe acute stroke patients even if they fail to receive treatment within 4.5 hours after onset or show no improvement after intravenous thrombolytic therapy.

As a minimally invasive procedure, intra-arterial thrombectomy is performed by neurosurgeons with special training, preferably within 9 hours after onset. To remove blood clots and restore blood supply to the brain, a catheter is inserted through the femoral artery in the groin to reach the intracranial artery via the aorta. The success rate can be up to 80 to 90 per cent.

Recent research shows good functional outcome in ischaemic stroke patients receiving intra-arterial thrombectomy within 16 hours or 24 hours after onset. This is especially important if the onset time is uncertain, e.g. when patients found to suffer from severe acute stroke only when they wake up.

Now with AI analysis of MRI or CT perfusion images, neurosurgeons can determine if intra-arterial thrombectomy is suitable for individual patients based on the amount and ratio of salvageable brain tissues. The amount of irreversibly damaged brain tissues increases with the time lapsed after onset.  The earlier the treatment, the better the clinical outcome and recovery.

The application of AI in stroke interventions not only extends the 3-hour time limit but also provides a viable option to those who show limited improvement after thrombolytic therapy. In view of the risk of blood vessel damage, clinical assessment will be conducted based on image analysis before treatment. Admission to ICU is also required after treatment to closely monitor the blood pressure and vital signs.

Acute Stroke Activation Programme (ASAP) 1.0 and 2.0

With ASAP 1.0 and 2.0, Hong Kong Sanatorium & Hospital is the first private hospital in Hong Kong to introduce acute stroke services and intra-arterial thrombectomy for ischaemic stroke patients.  It is also the first local medical institution to apply AI in stroke diagnosis and treatment.

Launched in 2016, ASAP 1.0 has so far treated over 110 cases with a comprehensive service package of stroke diagnosis and treatment. The programme comprises two major service components, i.e. assessment and treatment. Patients suspected of stroke are given priority in consultation by Resident Medical Officers at the Outpatient Department upon arrival. ASAP 1.0 will be activated if acute stroke is confirmed upon preliminary diagnosis. Priority CT brain scan will then be performed to confirm if the condition is haemorrhagic or ischaemic. An in-house neurologist will also be called for consultation and perform intravenous thrombolytic therapy for patients sent to the hospital within 3 hours of onset.  

ASAP 2.0 will be activated if no improvement is noted after intravenous thrombolytic treatment, or if one fails to arrive at the hospital within 3 hours after onset. Introduced in 2020, ASAP 2.0 adds to the original package with MRI or CT perfusion brain scan for detection of large vessel occlusion. With the latest AI software called “RapidAI”, the amount and ratio of salvageable and irreversibly damaged brain tissues can be calculated and assessed to determine one’s suitability for intra-arterial thrombectomy.

Patients will be transferred to ICU for close monitoring of blood pressure and vital signs for 48 hours after intra-arterial thrombectomy.  Multidisciplinary rehabilitation, which includes physiotherapy, occupational therapy, speech therapy and psychological counselling, will be arranged based on individual’s conditions and needs. 

MR/CT Brain perfusion scan plays an important role in evaluating infarction and ischaemia in acute stroke cases. MR/CT cerebral angiography further complements vascular assessment by determining the exact site of occlusion.

RapidAI formulates a mismatch map between diffusion and perfusion with the image data acquired. Brain region with substantial restricted diffusion (infarct core) and region with significant hypoperfusion are coloured in pink and green respectively. The green region minus the pink region is the salvageable brain tissue (ischaemic penumbra). A larger volume of penumbra means a greater volume of potentially salvageable brain tissue.

With readily available results and analysis, RapidAI enables clinicians to make faster, robust assessments and treatment decisions for acute stroke patients.

Prevention is Better than Cure

Lead a Healthy Life with High Stroke Awareness

Medical advance could be in a sense encouraging, but the consequences of acute stroke are always dire. It means the truism “Prevention is better than  cure” remains as important as ever. The key to acute stroke prevention is a  healthy lifestyle, e.g. quit smoking and drinking alcohol, do moderate exercise every day and maintain a balanced diet with “3 lows and 1 high”,  i.e. low sugar, low salt, low fat and high fibre.  Also stay alert to any signs of stroke  onset all the time, and for the best possible treatment outcome,  arrive at the hospital within 3 hours after onset.

Acute Stroke Management - FAST

• Face: slurred speech, difficulty in communication
• Arms: muscle numbness in one half of the body, asymmetrical facial expressions
• Speech: weakness in limbs of one half of the body
• Time: seek assessment and treatment immediately

Case Sharing

An 84-year-old patient became aware of right-sided limb weakness and slurred speech in early November 2020. He arrived at the Outpatient Department within an hour of symptom onset, and was immediately assessed and diagnosed with acute stroke by the Resident Medical Officer there. The patient was considered not suitable for intravenous thrombolytic therapy due to his medical history of atrial fibrillation and use of anticoagulant. He was therefore sent for MRI perfusion scanning, and thanks to the RapidAI software, the amount and ratio of salvageable and irreversibly damaged brain tissues could be calculated upon analysis. He was deemed eligible for intra-arterial thrombectomy, and showed good neurological recovery after treatment, especially in terms of speaking, swallowing abilities and limb power.  He was discharged from the hospital two and a half weeks later.