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      7T MRI in transient ischemic attacks: Have we only seen the tip of the iceberg?

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          Abstract

          Transient ischemic attack (TIA) has gained significant attention recently due to the increased incidence of subsequent stroke. However, there are many nonvascular clinical mimics of TIA, creating a need for improved biomarkers to identify a vascular origin. Following the recent approval of ultra-high field (UHF) 7T MRI in clinical practice, several clinical studies have highlighted its added utility in neuroimaging compared to lower-field 1.5T and 3T MRI, particularly in epilepsy and multiple sclerosis. Our case series of three patients with TIA illustrates that 7T MRI can depict small areas of intracortical microhemorrhages and microinfarctions, which could not be resolved with 3T or 1.5T MRI. There are currently no reports of intracortical localization of microhemorrhages in patients with TIA. This discovery may enhance our understanding and characterization of cerebrovascular abnormalities in TIAs. In addition, UHF imaging could potentially be utilized to distinguish transient neurological episodes secondary to cerebrovascular events from other differential considerations. Our cases highlight the underestimation of imaging abnormalities in cases of TIA and support the potential expanded application of clinical 7T to assess patients with TIA. Future studies are necessary at 7T redundant to determine the true incidence of such lesions in TIA and to examine the correlation between cortical microhemorrhages and subsequent ischemic stroke, hemorrhagic events, and neurocognitive impairment.

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          MR imaging detection of cerebral microbleeds: effect of susceptibility-weighted imaging, section thickness, and field strength.

          Brian Skehan, Laura-Jane Smith, Andrew S. Greenberg … (2009)
          The emergence of cerebral microbleeds (CMB) as common MR imaging findings raises the question of how MR imaging parameters influence CMB detection. To evaluate the effects of modified gradient recalled-echo (GRE) MR imaging methods, we performed an analysis of sequence, section thickness, and field strength on CMB imaging properties and detection in subjects with cerebral amyloid angiopathy (CAA), a condition associated with microhemorrhage. Multiple MR images were obtained from subjects with probable CAA, with varying sequences (GRE versus susceptibility-weighted imaging [SWI]), section thicknesses (1.2-1.5 versus 5 mm), and magnetic field strengths (1.5T versus 3T). Individual CMB were manually identified and analyzed for contrast index (lesion intensity normalized to normal-appearing white matter signal intensity) and diameter. CMB counts were compared between 1.5T thick-section GRE and thin-section SWI for 3 subjects who underwent both protocols in the same scanning session. With other parameters constant, use of SWI, thinner sections, and a higher field strength yielded medium-to-large gains in CMB contrast index (CI; Cohen d 0.71-1.87). SWI was also associated with small increases in CMB diameter (Cohen d <0.3). Conventional thick-section GRE identified only 33% of CMB (103 of 310) seen on thin-section SWI. Lesions prospectively identified on GRE had significantly greater CI and diameter measured on the GRE image than those not prospectively identified. The examined alternatives to conventional GRE MR imaging yield substantially improved CMB contrast and sensitivity for detection. Future studies based on these techniques will most likely yield even higher prevalence estimates for CMB.
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            Cerebral microbleeds and intracranial haemorrhage risk in patients anticoagulated for atrial fibrillation after acute ischaemic stroke or transient ischaemic attack (CROMIS-2): a multicentre observational cohort study

            Duncan Wilson, Gareth Ambler, Clare Shakeshaft … (2018)
            Summary Background Cerebral microbleeds are a potential neuroimaging biomarker of cerebral small vessel diseases that are prone to intracranial bleeding. We aimed to determine whether presence of cerebral microbleeds can identify patients at high risk of symptomatic intracranial haemorrhage when anticoagulated for atrial fibrillation after recent ischaemic stroke or transient ischaemic attack. Methods Our observational, multicentre, prospective inception cohort study recruited adults aged 18 years or older from 79 hospitals in the UK and one in the Netherlands with atrial fibrillation and recent acute ischaemic stroke or transient ischaemic attack, treated with a vitamin K antagonist or direct oral anticoagulant, and followed up for 24 months using general practitioner and patient postal questionnaires, telephone interviews, hospital visits, and National Health Service digital data on hospital admissions or death. We excluded patients if they could not undergo MRI, had a definite contraindication to anticoagulation, or had previously received therapeutic anticoagulation. The primary outcome was symptomatic intracranial haemorrhage occurring at any time before the final follow-up at 24 months. The log-rank test was used to compare rates of intracranial haemorrhage between those with and without cerebral microbleeds. We developed two prediction models using Cox regression: first, including all predictors associated with intracranial haemorrhage at the 20% level in univariable analysis; and second, including cerebral microbleed presence and HAS-BLED score. We then compared these with the HAS-BLED score alone. This study is registered with ClinicalTrials.gov, number NCT02513316. Findings Between Aug 4, 2011, and July 31, 2015, we recruited 1490 participants of whom follow-up data were available for 1447 (97%), over a mean period of 850 days (SD 373; 3366 patient-years). The symptomatic intracranial haemorrhage rate in patients with cerebral microbleeds was 9·8 per 1000 patient-years (95% CI 4·0–20·3) compared with 2·6 per 1000 patient-years (95% CI 1·1–5·4) in those without cerebral microbleeds (adjusted hazard ratio 3·67, 95% CI 1·27–10·60). Compared with the HAS-BLED score alone (C-index 0·41, 95% CI 0·29–0·53), models including cerebral microbleeds and HAS-BLED (0·66, 0·53–0·80) and cerebral microbleeds, diabetes, anticoagulant type, and HAS-BLED (0·74, 0·60–0·88) predicted symptomatic intracranial haemorrhage significantly better (difference in C-index 0·25, 95% CI 0·07–0·43, p=0·0065; and 0·33, 0·14–0·51, p=0·00059, respectively). Interpretation In patients with atrial fibrillation anticoagulated after recent ischaemic stroke or transient ischaemic attack, cerebral microbleed presence is independently associated with symptomatic intracranial haemorrhage risk and could be used to inform anticoagulation decisions. Large-scale collaborative observational cohort analyses are needed to refine and validate intracranial haemorrhage risk scores incorporating cerebral microbleeds to identify patients at risk of net harm from oral anticoagulation. Funding The Stroke Association and the British Heart Foundation.
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              Cerebral microbleeds and recurrent stroke risk: systematic review and meta-analysis of prospective ischemic stroke and transient ischemic attack cohorts.

              Zoe Fox, Andreas Charidimou, David J. Werring … (2013)
              To evaluate cerebral microbleeds (CMBs) and future stroke risk (including intracerebral hemorrhage [ICH]) in patients with ischemic stroke (IS) or transient ischemic attack. A systematic review and meta-analysis of prospective cohorts with recent IS/transient ischemic attack. We critically appraised studies and calculated pooled odds ratios (ORs), using the Mantel-Haenszel fixed-effects method, for ICH or recurrent IS, in patients with versus without CMBs. We pooled data from 10 cohorts, including 3067 patients. CMBs were associated with a significant increased risk of any recurrent stroke (OR, 2.25; 95% confidence interval [95% CI], 1.70-2.98; P<0.0001), ICH (OR, 8.52; 95%CI, 4.23-17.18; P=0.007), and IS (OR, 1.55; 95%CI, 1.12-2.13; P<0.0001). When stratified by study population ethnicity (Asian versus Western [mainly white European]), the association of CMBs with ICH was significant for Asian cohorts (5 studies; n=1915; OR, 10.43; 95%CI, 4.59-23.72; P<0.0001) but borderline and of lower magnitude for Western cohorts (4 studies; n=885; OR, 3.87; 95%CI, 0.91-16.4; P=0.066). By contrast, there was a significant association of CMBs with recurrent IS in Western (3 studies; n=899) but not Asian cohorts (4 studies; n=1357; OR, 2.23; 95%CI, 1.29-3.85; P=0.004 compared with OR, 1.30; 95%CI, 0.88-1.93; P=0.192, respectively). There is consistent evidence of an increased risk of recurrent stroke after IS or transient ischemic attack in patients with CMBs. The risk for spontaneous ICH appears to be greater than the risk for recurrent IS. Our findings also suggest that the balance of risk for ICH versus IS differs between Asian and Western cohorts.
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                Author and article information

                Contributors
                Dhairya A Lakhani: (View ORCID Profile)
                Erik H Middlebrooks: (View ORCID Profile)
                Journal
                Title: The Neuroradiology Journal
                Abbreviated Title: Neuroradiol J
                ISSN (Print): 1971-4009
                ISSN (Electronic): 2385-1996
                Publication date (Electronic): March 27 2023
                Page: 197140092311660
                Affiliations
                [1 ]Department of Radiology, West Virginia University, Morgantown, WV, USA
                [2 ]Department of Radiology, Mayo Clinic, Jacksonville, FL, USA
                [3 ]Department of Neurology, Mayo Clinic, Jacksonville, FL, USA
                Article
                DOI: 10.1177/19714009231166089
                SO-VID: ae5469ef-1f6a-48ca-a3df-a5fa6d74421f
                Copyright © © 2023
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