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Type:
Educational Exhibit
Keywords:
Abdomen, Liver, MR, CT, Ultrasound, Diagnostic procedure, Neoplasia, Tissue characterisation
Authors:
B. M. Araujo, F. Rego Costa, A. Carvalho, L. Melão; Porto/PT
DOI:
10.1594/ecr2015/C-0804
Background
The group of liver lesions containing fat is wide including benign and malignant.
The fat may be present as macroscopic fat or intracellular lipid.
Ultrasound (US) is usually the first approach of liver lesions.
The fat usually appears hyperechoic at US and,
as the fat attenuates more than normal liver parenchyma,
partial acoustic shadowing may occur deep to fat-containing lesions [1].
However hyperechogenicity may be found in non-fat-containing lesions and subsequent characterization with CT,
MRI or even biopsy is usually necessary.
Macroscopic fat-containing lesions are usually easily characterized on CT by presenting areas of low attenuation compared with normal liver parenchyma,
ranging between -10 and -100 Hounsfield Units [2].
However sometimes the lack of sufficient lipid pixels may prevent adequate characterization.
At MRI macroscopic fat demonstrate hyperintensity on T1- and T2-weighted images with signal loss on fat-saturated MR images.
Intracellular lipid containing lesions can be characterized by chemical shift MRI imaging with opposed-phase gradient-echo (GRE) sequences [3].
During the in-phase imaging the signals of water and lipid are addictive.
In intermediate echo times,
lipid and water protons are out of phase leading to phase cancellation effect at a voxel and resulting in signal loss in voxels with water and fat.