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A non-invasive magnetic resonance imaging approach for assessment of real-time microcirculation dynamics.

ABSTRACT: We present a novel, non-invasive magnetic resonance imaging (MRI) technique to assess real-time dynamic vasomodulation of the microvascular bed. Unlike existing perfusion imaging techniques, our method is sensitive only to blood volume and not flow velocity. Using graded gas challenges and a long-life, blood-pool T 1-reducing agent gadofosveset, we can sensitively assess microvascular volume response in the liver, kidney cortex, and paraspinal muscle to vasoactive stimuli (i.e. hypercapnia, hypoxia, and hypercapnic hypoxia). Healthy adult rats were imaged on a 3 Tesla scanner and cycled through 10-minute gas intervals to elicit vasoconstriction followed by vasodilatation. Quantitative T 1 relaxation time mapping was performed dynamically; heart rate and blood oxygen saturation were continuously monitored. Laser Doppler perfusion measurements confirmed MRI findings: dynamic changes in T 1 corresponded with perfusion changes to graded gas challenges. Our new technique uncovered differential microvascular response to gas stimuli in different organs: for example, mild hypercapnia vasodilates the kidney cortex but constricts muscle vasculature. Finally, we present a gas challenge protocol that produces a consistent vasoactive response and can be used to assess vasomodulatory capacity. Our imaging approach to monitor real-time vasomodulation may be extended to other imaging modalities and is valuable for investigating diseases where microvascular health is compromised.

SUBMITTER: Ganesh T

PROVIDER: S-EPMC5547069 | biostudies-other | 2017 Aug

REPOSITORIES: biostudies-other

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Project description:Background & aimsHepatic venous pressure gradient (HVPG) measurement is currently the only validated technique to accurately evaluate changes in portal pressure. In this study, we evaluate the use of non-contrast quantitative magnetic resonance imaging (MRI) as a surrogate measure of portal pressure.MethodsThirty patients undergoing HVPG measurement were prospectively recruited. MR parameters of longitudinal relaxation time (T1), perfusion of the liver and spleen (by arterial spin labelling), and blood flow in the portal, splanchnic and collateral circulation (by phase contrast MRI) were assessed. We estimated the liver stiffness measurement (LSM) and enhanced liver fibrosis (ELF) score. The correlation of all non-invasive parameters with HVPG was evaluated.ResultsThe mean (range) HVPG of the patients was 9.8 (1-22) mmHg, and 14 patients (48%) had clinically significant portal hypertension (CSPH, HVPG ⩾10mmHg). Liver T1 relaxation time, splenic artery and superior mesenteric artery velocity correlated significantly with HVPG. Using multiple linear regression, liver T1 and splenic artery velocity remained as the two parameters in the multivariate model significantly associated with HVPG (R=0.90, p<0.001). This correlation was maintained in patients with CSPH (R=0.85, p<0.001). A validation cohort (n=10) showed this linear model provided a good prediction of HVPG. LSM and ELF score correlated significantly with HVPG in the whole population but the correlation was absent in CSPH.ConclusionsMR parameters related to both hepatic architecture and splanchnic haemodynamics correlate significantly with HVPG. This proposed model, confirmed in a validation cohort, could replace the invasive HVPG measurement.Lay summaryIn patients with cirrhosis, the development and progression of portal hypertension is related to worse outcomes. However, the standard technique of assessing portal pressure is invasive and not widely used in clinical practice. Here, we have studied the use of non-invasive MRI in evaluating portal pressure. The MRI measures of liver architecture and blood flow in the splenic artery correlated well with portal pressure. Therefore, this non-invasive method can potentially be used to assess portal pressure in clinical trials and monitoring treatment in practice.

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A non-invasive magnetic resonance imaging approach for assessment of real-time microcirculation dynamics.

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