Quantification of intrapancreatic fat in type 2 diabetes by MRI

Abstract

ObjectivesAccumulation of intrapancreatic fat may be important in type 2 diabetes, but widely varying data have been reported. The standard quantification by MRI in vivo is time consuming and dependent upon a high level of experience. We aimed to develop a new method which would minimise inter-observer variation and to compare this against previously published datasets.MethodsA technique of ‘biopsying’ the image to minimise inclusion of non-parenchymal tissues was developed. Additionally, thresholding was applied to exclude both pancreatic ducts and intrusions of visceral fat, with pixels of fat values of <1% or >20% being excluded. The new MR image ‘biopsy’ (MR-opsy) was compared to the standard method by 6 independent observers with wide experience of image analysis but no experience of pancreas imaging. The effect of the new method was examined on datasets from two studies of weight loss in type 2 diabetes.ResultsAt low levels of intrapancreatic fat neither the result nor the inter-observer CV was changed by MR-opsy, thresholding or a combination of the methods. However, at higher levels the conventional method exhibited poor inter-observer agreement (coefficient of variation 26.9%) and the new combined method improved the CV to 4.3% (p<0.03). Using either MR-opsy alone or with thresholding, the new methods indicated a closer relationship between decrease in intrapancreatic fat and fall in blood glucose.ConclusionThe inter-observer variation for quantifying intrapancreatic fat was substantially improved by the new method when pancreas fat levels were moderately high. The method will improve comparability of pancreas fat measurement between research groups.

The role of physical activity in metabolic homeostasis before and after the onset of type 2 diabetes: an IMI DIRECT study

“…A core feature of the TC relates to the role of islet triacylglycerol content in beta cell lipotoxicity, leading to diminished beta cell function [16]. As beta cells are estimated to account for only a small fraction of total pancreatic volume (<5% [37]), MRI imaging of the pancreas may be too insensitive to specifically quantify beta cell triacylglycerol content, with the signal instead being driven by whole pancreas fat content [38]. Furthermore, the serrations and involutions that characterise some pancreases [39] make the accurate assessment of ectopic fat near the boundary of the organ challenging, even using whole-organ MRI techniques and experienced radiographers identifying organ boundaries, as was the case here.…”

Na dobre i na złe – czyli rola oddziaływania trzustki, śródbłonka i tkanki tłuszczowej w regulacji funkcjonowania komórek β i rozwoju cukrzycy typu 2 związanej z otyłością

“…Larger fat deposits were observed in the body and tail than in the head of the pancreas [11]. Intrapancreatic fat content differs significantly between prediabetic and diabetic individuals, with a continuous increase in the magnetic resonance imaging-detected proton-density fat fraction in healthy controls compared with subjects with established T2D [10,12]. In a Chinese cohort, a higher ratio of abdominal subcutaneous adipose tissue to VAT (SVR) exerted a beneficial effect on β-cell function and was related to improvements in insulin sensitivity status [13].…”

“…Hence, adipose tissue infiltration was enhanced with decreasing glucose tolerance [5]. Similar to metabolically active VAT, peripancreatic, interlobular, and intralobular adipose tissue infiltrates the pancreas [5,12] and alters insulin sensitivity and β-cell function through the release of various adipocytokines, inflammatory mediators, and vasoactive factors, including tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), IL-8, leptin, adiponectin, selectins, chemokines, visfatin, and resistin [22]. Chronic inflammation-mediated damage might result in significant parenchymal atrophy and the replacement of acinar cells with fat, thus affecting the size, volume, and contour of the pancreas in T2D individuals [23].…”

Obesity, metabolic disease and the pancreas—Quantitative imaging of pancreatic fat

“…Recent combinations of manual segmentation with thresholding have shown promising results with improved interobserver variation. 75 Pancreatic disease however is associated with dramatic morphological changes including fatty infiltration and atrophy. Changes in the distribution of intralobular, interlobular and extralobular pancreatic fat are regularly seen on cross-sectional imaging but remain poorly understood ( Figure 6).…”