Magnetic Resonance Imaging Using Ultrasmall Superparamagnetic Particles of Iron Oxide in Patients Under Surveillance for Abdominal Aortic Aneurysms to Predict Rupture or Surgical Repair: The MA3RS Study

Objectives
Ultrasmall superparamagnetic particles of iron oxide (USPIO) detect cellular inflammation and tissue-resident macrophages on magnetic resonance imaging (MRI). In patients with abdominal aortic aneurysm (AAA), we assessed whether USPIO-enhanced MRI can predict AAA growth and clinical outcomes.
Methods
In a prospective multicenter open-label imaging cohort study, we recruited 361 patients with AAA (diameter ≥40 mm) who underwent baseline USPIO-enhanced MRI. Patients were classified according to the presence of USPIO uptake in the wall of the AAA. All participants were monitored with serial ultrasound imaging and clinical follow-up for a minimum of 2 years. The primary end point was the composite of AAA rupture or repair.
Results
During baseline assessment, 19 patients were withdrawn by the attending clinician or at the participant’s request. The study population of 342 participants were predominantly male (293 [85%]), with a mean age of 73 ± 7 years and AAA diameter of 50 ± 8 mm. Mural USPIO uptake was indeterminate in five participants. During a mean follow-up of 1006 ± 279 days, there were 17 (5.0%) AAA ruptures, 126 (36.8%) AAA repairs, and 48 (14.0%) deaths. Compared to those without uptake, patients with mural USPIO uptake had increased AAA expansion (3.4 ± 2.4 vs 2.5 ± 2.4 mm/y; difference, 0.8 mm/y; 95% confidence intervals [CI] 0.22-1.39 mm/y; P = .007) and higher rates of AAA rupture or repair (69 of 146 [47.3%] vs 68 of 191 [35.6%]; difference, 11.7%; 95% CI, 1.1%-22.2%; P = .031). Similar findings were seen for rates of AAA rupture (10 of 146 [6.8%] vs 7 of 191 [3.7%]; difference, 3.2%; 95% CI, –1.7% to 8.1%; P = .186), surgical repair (61 of 146 [41.8%] vs 62 of 191 [32.5%]; difference, 9.5%; 95% CI, –1.1 to 19.7%; P = .078), and all-cause (26 of 146 [17.8%] vs 21 of 191 [11.0%]; difference, 6.8%; 95% CI, –0.8% to 14.4%; P = .074) and AAA-related (11 of 146 [7.5%] vs 6 of 191 [3.1%]; difference 4.4%; 95% CI, –0.6% to 9.3%; P = .068) mortality.
Conclusions
USPIO-enhanced MRI is a novel imaging biomarker of disease activity that predicts the rate of AAA growth and risk of AAA rupture or repair. In patients with AAA, USPIO-enhanced MRI has the potential to risk stratify, to determine clinical management, and to improve patient outcomes.