A novel perfusion imaging strategy for the ischaemic limb

• Main Author: Bajwa, Adnan Ahmad
• Other Authors: Modarai, Bijan ; Smith, Alberto
• Published: King's College London (University of London) 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.754916

Current assessment of peripheral arterial disease (PAD) is focused on delineating luminal narrowing or obstruction in the major lower limb blood vessels. The imaging modalities used do not provide information on the microcirculation or muscle perfusion in the affected limb, the most important determinants of limb salvage in patients with PAD. An objective, non-invasive method for measuring and mapping muscle perfusion would aid diagnosis in PAD. It would may also inform planning of revascularisation strategies and better determine success after revascularization, ultimately improving limb salvage. Blood Oxygenation Level Dependent Magnetic Resonance Imaging (BOLD-MRI) is a technique that has been used to measure perfusion in the brain, kidneys and heart. The utility of BOLD-MRI in the lower limb musculature has, to date, been limited by a lack of sensitivity and reproducibility. The present study aimed to develop BOLD-MRI as an objective and reproducible tool for measuring perfusion in the calf musculature. The calf was imaged at 3 Tesla in young healthy controls, age-matched controls, and patients with critical limb ischaemia (CLI). A cuff placed around the thigh was used during the scan to provoke hyperaemia. T2* Signal intensity time curves were generated for each muscle group and curve parameters, including signal reduction during ischemia (SRi) and gradient during reactive hyperaemia (Grad). BOLD-MRI was also used to assess changes in perfusion following revascularization in CLI patients. Muscle biopsies, obtained at the level of BOLD-MRI measurement and from healthy proximal muscle of patients undergoing lower limb amputation were analysed for capillary:fibre (C:F) ratio. Good interuser and interscan reproducibility was found for Grad and SRi. The ischaemic limb had lower Grad and SRi compared with the contralateral asymptomatic limb, age-matched controls, and young controls. Successful revascularisation consistently resulted in significant improvement in both Grad and SRi. There was a significant correlation between C:F ratio in muscle biopsies from amputated limbs and Grad measured preoperatively at the corresponding level. These data suggest that BOLD-MRI holds promise as a reliable tool for assessing perfusion in the lower limb and may allow refinement of current treatment algorithms. Its utility merits further investigation in a multi-centre clinical trial.