Synopsis
Abnormal lipid metabolism is associated with
obesity, resulting in accumulation of fat in non-adipose tissues – a process
called steatosis. Steatosis has long been known to occur in the liver and
skeletal muscle, but also occurs in other organs including the pancreas, heart,
and the kidneys, with potential significant pathophysiological implications. In
this educational session, we will discuss the clinical significance of
extra-hepatic steatosis and the value of quantitative MR in its noninvasive
evaluation, as well as future research opportunities and technical challenges.HIGHLIGHTS
- Proton-density fat fraction is a standardized MR metric of tissue fat quantity,
and its applicability is not limited to liver
- Steatosis in extra-hepatic organs, such as pancreas,
heart, and kidneys may be important
- Quantitative MR may become a valuable research tool to
evaluate steatosis and lipotoxicity in extra-hepatic organs not amenable for
invasive biopsies
TARGET AUDIENCE
Clinical scientists interested in quantitative
MR imaging and spectroscopy in the body, in particular, quantitative fat
imaging
ABSTRACT
Abnormal lipid metabolism is associated with obesity,
resulting in accumulation of fat in non-adipose tissues [1]. This process called steatosis has long been known to occur in the liver and skeletal
muscles, which are major organs involved in lipid metabolism along with the
adipose tissue. In addition, recent research indicates that steatosis also
occurs in other organs, including the pancreas, heart, and the kidneys [1,2]. Steatosis
in these extra-hepatic organs may lead to impaired cell function, or lipotoxicity, and contribute to obesity-related
end-organ diseases, such as diabetes [3], cardiomyopathy [4,5], and chronic
kidney disease [2].
The gold standard method of steatosis evaluation
in any organ is invasive tissue sampling (e.g. biopsy) and ex-vivo histopathological examination. To allow safe, noninvasive,
and objective diagnosis of steatosis in-vivo,
a quantitative MR-based fat quantity called proton-density fat fraction (PDFF) has
been proposed. Accuracy,
reproducibility, and clinical utility of PDFF have been extensively validated in
the liver, and PDFF has become a valuable research tool in clinical trials of nonalcoholic
fatty liver disease, replacing liver biopsy as the primary endpoint [6].
Extrapolating from the validation results
in the liver, PDFF and related MR techniques have been applied for noninvasive
steatosis evaluation in extra-hepatic organs, including myocardium [7,8],
pancreas [9-11], and most recently, kidneys [11-13]. Compared to liver, a noninvasive method is critically
important in these organs, as biopsy is not clinically acceptable for steatosis
evaluation due to technical and risk considerations. While this unmet need
presents new opportunities for quantitative MR, we are also faced with organ-
and disease-specific technical challenges.
In
this educational session, we will discuss the pathophysiological significance
of extra-hepatic steatosis and the value of noninvasive MR fat quantification, as
well as future research opportunities and challenges.
Acknowledgements
No acknowledgement found.References
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