Ammad Mahmood, MBChB

European Stroke Organisation-World Stroke Organization 2020 Virtual Conference
November 7-9, 2020

This session covered a number of novel techniques used in stroke imaging with a number of distinguished speakers. Cutting-edge advances in pre-hospital imaging in the ambulance, imaging used in making decisions about reperfusion therapies, and diagnostic imaging used in aetiological classification were all discussed.

Pre-hospital imaging – Jeffrey Saver
Advantages of triage in the field of patients into ischemic (LVO and non-LVO) and hemorrhagic stroke enables routing to the most appropriate facility, minimizing delays to treatment access and the need for inter-hospital transfers. Quasi-imaging approaches involving innovative approaches such as radio frequency, infrared, or EEG ‘stroke helmets’ may help identify patients with LVO in the future. Ultrasound assessment of vessel patency in the field yielded 91% accuracy in identifying LVO in one study. Mobile stroke units with CT capability are already in use and allow CT, CTA, and possibly CTP in the field. Automated image processing software can aid in interpretation of CT results quickly. Future technologies may include mobile stroke units in helicopters or small aircraft, mobile neuro-intervention suites, and mobile MRI imaging. Prof. Saver presented some cases from the Los Angeles mobile stroke unit experience highlighting the optimization of patient management achieved through early triage. Lastly, he highlighted the ongoing BEST-MSU trial, which will evaluate the benefit of MSUs in stroke management in several cities in the United States.

Automated image processing software – Bruce Campbell
The advantages of using processing software include speed, improved sensitivity, and standardization of analysis, particularly in settings where local expertise in image interpretation may not be available. Based on clinical trials which have utilized CT perfusion analysed volumes as inclusion criteria, software can help identify patients eligible for thrombolysis and thrombectomy, particularly late window patients. Treatment decisions in groups such as minor stroke or patients with co-morbidities who may not fit usual trial criteria can be made easier by looking for a perfusion mismatch. Prof. Campbell highlighted the capabilities of several packages, including automated ASPECTS assessment, hypodensity volume estimation, hyperdense artery identification, hemorrhage identification, LVO detection, collateral assessment, and ischemic core and penumbra prediction.

Carotid plaque imaging – Marie-Luise Mono
Asymptomatic moderate to severe carotid stenosis or symptomatic mild carotid stenosis are both challenging scenarios when determining stroke aetiology. Detailed imaging of plaques can reveal features of vulnerable plaques, such as intra-plaque hemorrhage, which contribute to the enlargement of the lipid-rich necrotic core and rapid plaque progression. Modalities used can include CT, MRI, and ultrasound; MRI and ultrasound provide the best imaging of plaque characteristics. Whilst most of these techniques remain research-based, T1 MRI imaging is widely available and could be used to identify high-risk plaque.

Comprehensive cardiac assessment by CT – Keith Muir
Secondary prevention beyond antiplatelets and statin depends upon the aetiological mechanism identified by investigations after stroke. The cause is cryptogenic in a significant proportion of cases. The standard of investigation which needs to be completed before declaring a case ‘cryptogenic’ is not universal, and access to modalities of investigation is variable worldwide. Delayed aetiological diagnosis leads to delayed management during the period of greatest risk for recurrent stroke. One option for rapid, universally available, combined assessment of cardioembolic and large vessel disease is contrast CT extended beyond the aortic arch to include cardiac imaging. Prof. Muir presented results of the D-CCIST pilot study from our center in Glasgow, which compared comprehensive cardiovascular imaging (CCI) which comprised of cardiac CT, CTA arch to vertex, and 3T MRI brain at a single visit against routine imaging for patients presenting within 7 days of TIA or acute stroke. A significantly higher proportion of patients with CCI had a definite aetiology identified by day 7 though not at day 30. Time to access investigations was not different between groups, but the time to identification of the aetiological cause was significantly shorter in the CCI group (51 hours) vs routine (82 hours). A larger trial of this approach to determine whether it can reduce recurrent clinical events is warranted.

When is arterial wall imaging useful? – Catherine Oppenheim
While imaging of the vessels with angiography is widely used and interpreted in acute stroke, vessel wall imaging remains a specialized assessment. Prof. Oppenheim highlighted 4 cases where MRI assessment of the vessel wall was used to make the diagnosis. The T1 MRI sequences used are possible on most scanner types. The cases included progressive carotid stenosis with intraplaque hemorrhage; transient perivascular inflammation of the carotid artery (TIPIC syndrome); dissection of the basilar artery; and VZV related cerebral vasculitis in a patient with HIV.

Imaging in wake-up stroke – Jochen Fiebach
Lastly, one of the authors of the WAKE-UP trial described the concept of DWI-FLAIR mismatch, which was developed from serial MRI imaging of patients with known times of symptom onset. In this cohort, it became clear that the majority of patients with DWI lesions did not develop FLAIR lesions until around 4.5 hours. This led to the WAKE-UP trial, which demonstrated a clear benefit in functional outcome for patients with DWI-FLAIR mismatch receiving thrombolysis versus placebo. A helpful online training tool from the WAKE-UP cohort has also been developed, allowing trainees to analyze a set of scans from the trial for DWI-FLAIR mismatch.