Abdominal aortic aneurysms (AAAs) with focal inflammation have been reported to grow 3 times faster than those without ¹, while their diameters were similar. Ultrasmall superparamagnetic iron oxide (USPIO) particles can identify inflammation (macrophages) in vivo using MRI. USPIOs induce both T1 and T2* shortening. Previous studies have focused on the T2* effects, looking for signal voids or quantitative mapping with T2*-weighted images. Such techniques, however, have limited slice resolution (5mm) ¹. We aim to evaluate higher resolution techniques for USPIO imaging.Sequences: Four MRI sequences (Table 1) were evaluated at 3T: 1) Conventional 2D T2* mapping with 10 echoes; 5mm slice thickness; 2) T1 weighted 3D blood suppressed fast-spin echo with variable flip angle train (DANTE-SPACE) ²: 1.3mm isotropic resolution, it is predominately T1 weighted but also has T2* weighting given its long echo train; 3) T1 weighted 3D Volume Interpolated Breath-hold Examination (VIBE, a gradient echo sequence): 1.3x1.3x2.6mm, very small T2* weighting; and 4) T1 weighted Ultra short TE (UTE, 3D radial acquisition): 1.3mm isotropic resolution, nearly ‘pure’ T1 weighting. Phantom Study: A saline phantom with a range of USPIO concentrations (0.94mg Fe/L to 600mg Fe/L) was made to represent the possible concentrations of USPIO in vivo. Images were acquired with four sequences and the T2* values and signal intensities were measured and compared. Patient Studies: 24 patients with AAA disease (all male, age 69±4.7, maximal diameter 4.3±1.0cm) were imaged on a Siemens 3T Skyra scanner before and 2-3 days after USPIO injection. T2* mapping and DANTE-SPACE were used in all patients. VIBE and UTE were preliminarily evaluated in a few patients. Changes of T2* values and signal characteristics in different sequences were compared.Phantom Study: MRI signal strength is plotted relative to USPIO concentration for the four sequences (Figure 1). Both SPACE and VIBE show signal increase-and-drop curves, however with different peaks (7.5 versus 60mg Fe/L). UTE signal continually rises with increasing USPIO concentrations, whereas T2* values drop. T2* mapping is not very sensitive at either very low or very high concentrations, while 3D sequences provide additional information. Patient study: Patients were classified as four types based on SPACE signal change (I: no change; II: signal drop; III: signal enhance; IV: signal drop and enhance. Figure 2-4). Among all 24 patients, 16 were unchanged; 8 patients were observed T2* drop, and all showed SPACE signal drop or enhance (drop only: 3; enhance only: 3; drop and enhance: 2). Of patients with USPIO uptake, 5/8 (62.5%) subsequently had repair for progressive AAA disease, and only 2/16 (12.5%) had surgery in the patients group without sign of USPIO uptake.There was good agreement between SPACE signal increase/decrease and a decrease in T2* value. SPACE signal drop likely indicates high or intra-cellular concentration of USPIO, while signal enhancement likely indicates relatively low concentration of USPIO. These findings suggest that SPACE can be used for intracellular USPIO imaging, which has been associated with fast AAA growth ¹ , with the advantage of higher spatial resolution than conventional T2* imaging. A larger scale longitudinal study with histology validation is needed to confirm these findings. Signal change characterization can also be readily implemented in the clinical routine. The UTE technique is particularly appealing given its linear relationship with increased USPIO concentration permitting quantification of inflammation severity (Figure 5). Positive contrast methods are more robust than negative contrast methods, and are less sensitive to imaging artefacts. 3D radial acquisition of UTE sequence is also insensitive to motion. The potential of UTE sequence will be evaluated in future patient studies. Additional patients will be recruited and all patients will be followed with serial imaging and a relationship to clinical outcome will be sought.3D high resolution MRI can be used to identify USPIO uptake within AAA, with good agreement with traditional 2D T2* mapping method. These methods may help risk stratify patients with AAA disease by characterizing and quantifying inflammation.