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).