Classification of aneurysms based on uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO). MRI is performed at baseline then 24 h following intravenous administration of USPIO. USPIO causes a reduction in T2* and can be quantified by comparing co-registered T2* images pre- and post- USPIO administration, presented as change in T2* represented as colour maps (as above). 'Positive uptake' of USPIO is denoted by the red colour (thresholded at change in T2* of at least 71% between pre-and post-USPIO administration), whereas blue denotes areas of no positive uptake. Of note, ‘significant’ uptake (i.e. USPIO positive) is defined as at least one focal area of USPIO uptake corresponding to 10 or more contiguous voxels of positive signal change at the aneurysm wall; USPIO uptake at the periluminal area is not thought to be clinically significant. Image courtesy of Dr Rachel Forsythe, University of Edinburgh