Читать книгу Magnetic Resonance Microscopy - Группа авторов - Страница 55

The use of low-field MRI in the stroke setting has recently been reviewed [52] including for resource-limited settings [53]. Portable low-field MRI has been contemplated for ruling out a hemorrhagic stroke to allow immediate reperfusion with the injection of recombinant tissue plasminogen activator (rtPA), which would exacerbate any existing cerebral hemorrhage. However, CT currently performs this job well, including portable units in EDs and even specialized CT-equipped ambulances [54–58] dispatched when stroke is suspected. Although a portable MRI would also be capable of this “rule out a bleed” role, it is worth looking to the next step of stroke care to avoid simply replacing one capable mobile imaging modality for another. Successful new intravenous thrombolytic therapies as well as widening windows for treatment have led to catheter-based thrombectomy treatments following the initial rtPA treatment [59,60]. A “hub-and-spokes” model for treatment sites has emerged for this treatment. First, patients with suspected stroke are rushed to the nearest “spoke hospital” where they receive a CT to verify stroke and rule out hemorrhage for immediate administration of rtPA. In the few cities with CT-equipped ambulances (mobile stroke units), this treatment is received in the field. Following rtPA administration, the patient is then evaluated for transfer to a “hub” hospital for catheter-based thrombectomy [59,60]. This assessment uses CT angiography (CTA) to identify a large vessel occlusion (LVO) target in the anterior circulation and perfusion (CTP) to estimate infarct size. An infarct core size >70 cc both reduces the likely benefit of revascularization and establishes a risk for hemorrhage during the procedure. Unfortunately, the infarct size determination is difficult and imprecisely measured on CTP [61]. In contrast, diffusion MRI is the established gold standard for early infarct core volume assessment [61] but is not commonly available in EDs [62,63]. The time-critical nature of acute stroke care and the cost of transport underscore the need for improved POC MR imaging in the spoke hospital ED to determine the eligibility of the patient for transport to receive catheter-based thrombectomy.