Session chair: Bruce Campbell, University of Melbourn, Australia
Report by Klearchos Psychogios MD, MSc, PhDc, Stroke Unit Metropolitan Hospital, Athens
Novel Approaches in Prehospital Imaging: From Ultrasound to Mobile CT
Pr. Jeffrey Saver from UCLA started the session by presenting novel approaches to prehospital imaging. Imaging in the field can aid critical decisions in order to transfer the right patient to the right hospital. Patients with small vessel occlusions should be transferred to acute stroke ready hospitals or primary stroke centers, patients with large vessel occlusion should go to centers with an ability to perform mechanical thrombectomy and patients with intracranial hemorrhages will need neurosurgical facilities. He described some types of stroke helmets which use biometrics or transcranial ultrasound to assess vessel patency and tissue perfusion, albeit not yet ready for clinical employment. He then focused on certain aspects of CT scans used by mobile stroke units, which can be further assisted by artificial intelligence reading. He closed with the cluster control RCT from 5 EMS regions of USA which will assess the benefits of stroke treatment delivered in stroke mobile units. The final results will be presented in the International Stroke Conference on February 2021.
An Overview of Available Automated Post Processing Software
Pr. Bruce Campbell who chaired the session, provided an overview of the available automated post processing software. He started with the primary questions that imaging should answer timely, at the initial point of contact during an acute stroke. Automated software reduces missed diagnosis and treatment opportunities with improved inter-rater agreement and standardization. Moreover, current evidence for IVT>4.5h and EVT>6h is based on perfusion imaging post processed by automated software. It may also aid substantially clinical decisions of “marginal” cases (mild NIHSS, low ASPECTS, chronic LVO) and may be in future non reperfusion-based therapies. He provided some illustrative paradigms of available softwares which are already widespread use. Current imaging criteria are based on certain thresholds used in RCTS, however Pr Campbell pointed that we should possibly individualize core volume limits based on certain factors such as premorbid fitness, location of core (for example less eloquent areas) etc.
Current Role of Carotid Plaque Imaging
The talk by Pr. Maria Luise Mono focused on the current role of Carotid Plaque imaging. Nowadays, degree of stenosis is not the only determinant of clinical decisions for several reasons: risk of stroke in asymptomatic carotid stenosis has been steadily decreased due to improvement of medical therapy, non stenotic symptomatic carotid plaques play a key role in stroke etiology and also carotid plaque remodelling can result in outward expansion of the outer wall boundary. There is a shift of imaging to try to recognize characteristics of the “vulnerable plaque” like intraplaque hemorrhage and neovascularization. Contrast enhanced ultrasound and gray scale median plaque analysis provide useful information. Axial high resolution MRI by adding a special T1 sequence to the standard examination, is the gold standard for best depiction of wall features. Main limitations of the studies assessing high risk plaque features include the rather small sample sizes, the subjective and/or not reproducible risk markers tested and the lack of RCTs. There is also an increased prevalence of “high risk” carotid plaques in embolic stroke of undetermined source. Pr Mono concluded that the link between biomarkers of plaque vulnerability and their role in clinical decision making has to be established by ongoing prospective studies and RCTs.
Comprehensive Cardiovascular Assessment by CT
Pr. Keith Muir started his presentation upon comprehensive cardiovascular assessment, with the necessity to tailor individual prevention strategies according to certain stroke etiologies. According to TOAST conventional classification there is still a quarter of cryptogenic stroke with negative or incomplete evaluation. Moreover, investigation takes time and this was evident in recent ESUS trials (NAVIGATE ESUS and RESPECT ESUS) where a 1.5 month median interval between stroke and enrollment was observed. This period is crucial as many stroke recurrences (especially in large artery arterosclerosis) take place during the first few weeks after the index stroke. Pr. Muir and his colleagues conducted a pilot study (D-CCIST) with the main hypothesis that a cardiac CT included in a single visit cardiovascular imaging (CCI) protocol, will shorten the time to reach mechanistic diagnosis in patients with minor stroke or TIA. The investigators used proportion of patients with stroke of uncertain etiology based on ASCOD system classification, as the primary endpoint. CCI protocol incorporated an ECG gated helical cardiac CT along with the arch and carotid CTA. The main conclusion of the study was that CCI reduced the proportion of unknown mechanism cases in a timely manner. However, investigation to explore potential to reduce clinical events is further warranted.
Beyond the Lumen: When Is Arterial Wall Imaging Useful? Interactive Cases
Pr Catherine Oppenheim gave an excellent presentation of the diagnostic potency of arterial vessel wall imaging (VWI) by providing some illustrative case reports. The first one was an 86-years old man with recurrent minor stroke due to carotid atherosclerosis. VWI demonstrated that the progression of the carotid stenosis was due to an intraplaque hemorrhage. The second was a 36-year-old patient with cervicalgia and headache. CT angiography and conventional MRA were inconclusive, whereas VWI MRI showed an extensive perivascular inflammation, compatible with a TIPIC syndrome (Transient Perivascular Inflammation of the Carotid artery). The third case was a 41 years old woman with multiple ischemic lesions. Brain MRA showed multiple intracranial stenosis with circumferential arterial wall enhancement on VWI, compatible with an infectious vasculitis. The last case highlighted the ability of a fusion Time of Flight and T1+Gadolinium VWI to demonstrate temporal arteritis.
Stroke of Unknown Onset: Imaging-Based Selection for Reperfusion Therapies
The final talk by Pr Jochen Fiebach was focused on stroke of unknown onset and imaging-based selection for reperfusion therapies. PRE FLAIR study showed that signal intensity becomes positive after 4.5h in the majority of patients with unknown stroke onset. This gave support to the FLAIR – DIFFUSION mismatch concept which was tested by the WAKE UP trial. Pr Fiebach also presented some illustrative cases of FLAIR positive and FLAIR negative patients as well as pitfalls in image interpretation. WAKE UP investigators have also developed a usefool training tool available on http://wakeuptrainingtool.com.