Twenty-six male
apoE(-/-) mice received saline or ANG II (1000 or 500 ng/kg/min) infusion for 14 days. All animals underwent MRI scanning following administration of
SPIO with the exception of three mice in the 1000 ng ANG II group, which were scanned without
SPIO administration. MR imaging was performed using black-blood T2 to
proton density -weighted multi-spin multi-echo sequence. In vivo MRI measurement of
SPIO uptake and abdominal aortic diameter were obtained.
Prussian blue, CD68,α-SMC and MAC3 immunohistological stains were used for the detection of
SPIO, macrophages and smooth muscle cells. ANG II infusion with 1000 ng/kg/min induced AAA in all of the
apoE(-/-) mice. ANG II infusion exhibited significantly higher degrees of
SPIO uptake, which was detected using MRI as a distinct loss of signal intensity. The contrast-to-noise ratio value decreased in proportion to an increase in the number of
iron-laden macrophages in the
aneurysm. The aneurysmal vessel wall in both groups of ANG II treated mice contained more
iron-positive macrophages than saline-treated mice. However, the presence of cells capable of phagocytosing haemosiderin in mural thrombi also induced low-signal-intensities via MRI imaging.
CONCLUSIONS/SIGNIFICANCE:
SPIO is taken up by macrophages in the shoulder and the outer layer of AAA. This alters the MRI signaling properties and can be used in imaging
inflammation associated with AAA. It is important to compare images of the aorta before and after
SPIO injection.