Abstract
BackgroundSusceptibility-weighted imaging (SWI) is a relatively new magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification, as a new source of contrast enhancement. This pictorial review is aimed at illustrating and discussing its main clinical applications.MethodsSWI is based on high-resolution, three-dimensional (3D), fully velocity-compensated gradient-echo sequences using both magnitude and phase images. A phase mask obtained from the MR phase images is multiplied with magnitude images in order to increase the visualisation of the smaller veins and other sources of susceptibility effects, which are displayed at best after post-processing of the 3D dataset with the minimal intensity projection (minIP) algorithm.ResultsSWI is very useful in detecting cerebral microbleeds in ageing and occult low-flow vascular malformations, in characterising brain tumours and degenerative diseases of the brain, and in recognizing calcifications in various pathological conditions. The phase images are especially useful in differentiating between paramagnetic susceptibility effects of blood and diamagnetic effects of calcium. SWI can also be used to evaluate changes in iron content in different neurodegenerative disorders.ConclusionSWI is useful in differentiating and characterising diverse brain disorders.
Highlights
Susceptibility weighted imaging (SWI) is a relatively new magnetic resonance (MR) technique that provides innovative sources of contrast enhancement visualising the changes in magnetic susceptibility that are caused by different substances like iron, haemorrhage or calcium
Deoxyhaemoglobin can behave like a contrast agent with long TEs for differentiating arteries from small veins, which can be as small as 100–200 μm and difficult to detect with conventional MR angiography techniques, such as time of flight (TOF) or phase contrast (PC) [3]
MR imaging (MRI) with GE sequences has been extensively used in the past for investigating young patients with traumatic brain injuries (TBI), either in the acute phase, when the clinical picture of a severe coma is not explained by Computed tomography (CT), or months after trauma, in order to understand the causes of an unsuccessful recovery
Summary
Susceptibility weighted imaging (SWI) is a relatively new magnetic resonance (MR) technique that provides innovative sources of contrast enhancement visualising the changes in magnetic susceptibility that are caused by different substances like iron, haemorrhage or calcium. Deoxyhaemoglobin can behave like a contrast agent with long TEs for differentiating arteries from small veins, which can be as small as 100–200 μm and difficult to detect with conventional MR angiography techniques, such as time of flight (TOF) or phase contrast (PC) [3]. For this reason, the phase-added information that is usually not available in the conventional magnitude image makes SWI well suited for the visualisation of very small vessels such as the caput medusae of venous angiomas and telangiectasias as a result of a combination of slow flow with changes in deoxyhaemoglobin concentration [4]. This pictorial essay is aimed at showing the most relevant clinical applications of SWI
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