MR signal-fat-fraction analysis and T2*weighted imaging measure BAT reliably on humans without cold exposure

Objective. Brown adipose tissue (BAT) is compositionally distinct from white adipose tissue (WAT) in terms of triglyceride and water content. In adult humans, the most significant BAT depot is localized in the supraclavicular area. Our aim is to differentiate brown adipose tissue from white adipose tissue using fat T2* relaxation time mapping and signal-fat-fraction (SFF) analysis based on a commercially available modified 2-point-Dixon (mDixon) water fat separation method. We hypothesize that magnetic resonance (MR) imaging can reliably measure BAT regardless of the cold-induced metabolic activation, with BAT having a significantly higher water and iron content compared to WAT.Material and methods. The supraclavicular area of 13 volunteers was studied on 3 T PET-MRI scanner using T2* relaxation time and SFF mapping both during cold exposure and at ambient temperature; and F-18-FDG PET during cold exposure. Volumes of interest (VOIs) were defined semiautomatically in the supraclavicular fat depot, subcutaneous WAT and muscle.Results. The supraclavicular fat depot (assumed to contain BAT) had a significantly lower SFF and fat T2* relaxation time compared to subcutaneous WAT. Cold exposure did not significantly affect MR-based measurements. SFF and T2* values measured during cold exposure and at ambient temperature correlated inversely with the glucose uptake measured by 18F-FDG PET.Conclusions. Human BAT can be reliably and safely assessed using MRI without cold activation and PET-related radiation exposure. (C) 2017 Elsevier Inc. All rights reserved

Measurement of brown adipose tissue mass using a novel dual-echo magnetic resonance imaging approach: A validation study

ObjectiveThe aim of this study was to evaluate and validate magnetic resonance imaging (MRI) for the visualization and quantification of brown adipose tissue (BAT) in vivo in a rat model. We hypothesized that, based on differences in tissue water and lipid content, MRI could reliably differentiate between BAT and white adipose tissue (WAT) and could therefore be a possible alternative for 18 F-Fluorodeoxyglucose Positron Emission Tomography (18FDG-PET), the current gold standard for non-invasive BAT quantification.Materials/MethodsEleven rats were studied using both 18FDG-PET/CT and MRI (1.5 T). A dual echo (in-and-out-of-phase) sequence was used, both with and without spectral presaturation inversion recovery (SPIR) fat suppression (DUAL-SPIR) to visualize BAT, after which all BAT was surgically excised. The BAT volume measurements obtained via 18FDG-PET/CT and DUAL-SPIR MR were quantitatively compared with the histological findings. All study protocols were reviewed and approved by the local ethics committee.ResultsThe BAT mass measurements that were obtained using DUAL-SPIR MR subtraction images correlated better with the histological findings (P = 0.017, R = 0.89) than did the measurements obtained using 18FDG-PET/CT (P = 0.78, R = 0.15), regardless of the BAT metabolic activation state. Additionally, the basic feasibility of the DUAL-SPIR method was demonstrated in three human pilot subjects.ConclusionsThis study demonstrates the potential for MRI to reliably detect and quantify BAT in vivo. MRI can provide information beyond that provided by 18FDG-PET imaging, and its ability to detect BAT is independent of its metabolic activation state. Additionally, MRI is a low-cost alternative that does not require radiation

Brown adipose tissue triglyceride content is associated with decreased insulin sensitivity, independently of age and obesity

The aim of the present study was to determine whether single-voxel proton magnetic resonance spectroscopy (H-1-MRS) can non-invasively assess triglyceride content in both supraclavicular fat depots and subcutaneous white adipose tissue (WAT) to determine whether these measurements correlate to metabolic variables. A total of 25 healthy volunteers were studied using F-18-fluorodeoxyglucose positron emission tomography (PET) and O-15-H2O PET perfusion during cold exposure, and H-1-MRS at ambient temperature. Image-guided biopsies were collected from nine volunteers. The supraclavicular triglyceride content determined by H-1-MRS varied between 60 and 91% [mean +/- standard deviation (s.d.) 77 +/- 10%]. It correlated positively with body mass index, waist circumference, subcutaneous and visceral fat masses and 8-year diabetes risk based on the Framingham risk score and inversely with HDL cholesterol and insulin sensitivity (M-value; euglycaemic-hyperinsulinaemic clamp). Subcutaneous WAT had a significantly higher triglyceride content, 76-95% (mean +/- s.d. 87 +/- 5%; p = 0.0002). In conclusion, the triglyceride content in supraclavicular fat deposits measured by H-1-MRS may be an independent marker of whole-body insulin sensitivity, independent of brown adipose tissue metabolic activation

The Evolution of Knowledge Clusters

The economic downturn post-2000 badly undermined the rapid growth of knowledge-based and technology-led sectors. This article reflects on post- and pre-2000 development from the perspective of the evolution of regional clusters of knowledge-based activity. Four case studies of knowledge clusters are presented—Silicon Valley (United States), Cambridge (United Kingdom), Ottawa (Canada), and Helsinki (Finland)—as a means of understanding how the modus operandi of such clusters is evolving. The author finds that knowledge cluster development is shifting from one of internal reliance to models based on wider connectivity and consolidation. It is these new patterns of connected clusters and broadened knowledge networks that both firms and policy makers are increasingly attempting to foster. A framework outlining the key stages of evolution through which knowledge clusters advance is proposed. The author concludes that cluster policies must be increasingly attuned to positioning within a global network environment