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ECR 2018 / C-2687
Focal and diffuse hyperintense hepatic lesions on unenhanced T1-weighted MR images: a pictorial essay
Congress: ECR 2018
Poster No.: C-2687
Type: Educational Exhibit
Keywords: Parasites, Metabolic disorders, Haemangioma, Contrast agent-intravenous, Chemoembolisation, Biopsy, MR, Liver, Anatomy, Abdomen
Authors: L. Mammino1, D. C. Caltabiano1, V. Costanzo1, M. Coronella1, G. Mazzone2, P. V. Foti1, P. Milone1, A. Basile1, S. Palmucci1; 1Catania/IT, 2Sant'agata Li Battiati (CT)/IT
DOI:10.1594/ecr2018/C-2687

Background

Signal intensity of T1 weighted images is due to several factors such as the chemical composition of tissues, scanning sequences parameters and use of contrast medium [1].

T1 tissue relaxation time is the main factor that sets signal intensity in Magnetic Resonance Imaging (MRI) [1]. Normal liver tissue has a short T1 relaxation time [2]: for this reason, only lesions that contain T1-shortening  elements appear relatively hyperintense.

Below are the most common causes of T1 hyperintensity:

-Due to its short T1 relaxation time, fat is the most common element that increases T1-weighted images signal in liver lesions [3]: intracellular/microscopic fat can be detected using MR sequences based on chemical shift (signal loss in out-of-phase images); macroscopic fat, instead may be detected using fat-suppressed T1-weighted images (no signal loss in out-images; india ink sign; hypointensity in fat-sat images) [4-5].

-Proteins in macromolecular compounds can bind water molecules, resulting in a restriction of motion and shortening of T1 relaxation time [6].

- Paramagnetic effect of haemoglobin degradation product, copper and melanin induce shorter T1 relaxation time in liver lesions  [7-8-9].

- Sinusoids dilatation is associated with T1 hyperintensity, but the associated mechanism is not completely understood: probably it depends on increased blood viscosity or intra-sinusoid thrombosis [10].

Even when a liver lesion does not have a short T1 relaxation time, it may appear relatively hyperintense if the liver tissue has low signal because of fibrosis, iron overload or edema [11-12].

Lastly, phase-encoded motion artifacts should not be confused as real focal liver lesions. These artifacts, due to arterial pulsation, breathing or patient’s movement, manifest as faded T1 hyperintense area (ghost artifact). 

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