|ECR 2018 / C-2687|
|Focal and diffuse hyperintense hepatic lesions on unenhanced T1-weighted MR images: a pictorial essay|
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 .
T1 tissue relaxation time is the main factor that sets signal intensity in Magnetic Resonance Imaging (MRI) . Normal liver tissue has a short T1 relaxation time : 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 : 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 .
- 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 .
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).
Thematically related posters
ECR 2018 / C-0753
Hepatic cavernous hemangiomas: long-term (>5 years) follow-up changes on contrast-enhanced dynamic computed tomography or magnetic resonance imaging and determinant factors of the size change