Fat Quantification in the Abdomen

Abstract

Fatty liver disease is characterized histologically by hepatic steatosis, the abnormal accumulation of lipid in hepatocytes. It is classified into alcoholic fatty liver disease and non-alcoholic fatty liver disease, and is an increasingly important cause of chronic liver disease and cirrhosis. Assessing the severity of hepatic steatosis in these conditions is important for diagnostic and prognostic purposes, as hepatic steatosis is potentially reversible if diagnosed early. The gold standard for assessing hepatic steatosis is liver biopsy, which is limited by sampling error, its invasive nature, and associated morbidity. As such, non-invasive imaging-based methods of assessing hepatic steatosis are needed. Ultrasound and CT are able to suggest the presence of hepatic steatosis based on imaging features, but are unable to accurately quantify hepatic fat content. Since Dixon’s seminal work in 1984, MRI has been used to compute the signal fat fraction from chemical-shift-encoded imaging, commonly implemented as out-of-phase and in-phase imaging. However, signal fat fraction is confounded by several factors that limit its accuracy and reproducibility. Recently, advanced chemical-shift-encoded MRI methods have been developed that address these confounders and are able to measure the proton density fat fraction (PDFF), a standardized, accurate, and reproducible biomarker of fat content. The use of these methods in the liver, as well as in other abdominal organs such as the pancreas, adrenal glands, and adipose tissue will be discussed in this review.

Liver fat imaging—a clinical overview of ultrasound, CT, and MR imaging

“…These confounders on MRI are R2* decay, the complexity of the fat spectrum and T 1 weighting due to the differing T 1 values of fat and water. 57,60 Confounder corrected chemical shift-encoded MRI corrects for these three confounders by collecting images at multiple echo times with low flip angle to minimise T 1 weighting and by incorporating the multi-peak structure of fat in the analysis algorithm. 57,61,62 The end result is the PDFF, which is the (liver fat signal)/(total signal).…”

Changes in Tissue Composition and Load Response After Transtibial Amputation Indicate Biomechanical Adaptation

“…5 These observations reflect the well-established changes in tissue composition associated with muscle atrophy post-amputation associated with denervation and disuse. 28,51,58 However, this study has proved novel in discriminating between superficial and adipose infiltrating muscle tissues in residual limbs, thus providing insight into the potential for both disease progression 1,20,21 and an enhanced risk for DTI. 37,52,57 Correlation analysis provided insights into the relationships between tissue composition in the contralateral and residual limbs and intrinsic factors associated with the individuals post-amputation (Table 2).…”

<p>MRI assessment of ectopic fat accumulation in pancreas, liver and skeletal muscle in patients with obesity, overweight and normal BMI in correlation with the presence of central obesity and metabolic syndrome</p>

“…Excess fat accumulation results in the development of an elevated number of many serious health problems, including metabolic syndrome (MetS), type 2 diabetes (T2DM) and cardiovascular disease, and correlates significantly with increased mortality 13–17. A particularly important problem is MetS associated with obesity, which consists of at least three of these five abnormalities: (1) central obesity; (2) high triglyceride (TG) level; (3) decreased HDL cholesterol level; (4) high blood pressure; and (5) elevated fasting glucose level or previously diagnosed metabolic disorders 18,19…”