Optimizing the ferumoxytol dose for vascular suppression in brachial plexus magnetic resonance neurography

<i>Background.</i>Magnetic resonance neurography (MRN) enables visualization of peripheral nerves using T2-weighted, fat-suppressed sequences. However, vascular signal contamination in the brachial plexus remains a challenge. Ferumoxytol, an ultra-small paramagnetic iron oxide agent, can suppress vascular signal in MRN due to its high T2 relaxivity and longer half-life, but the optimal dose is unknown.<i>Objective.</i>To evaluate whether a subject-specific dose of Ferumoxytol, based on weight and estimated blood volume, improves vascular suppression in brachial plexus MRN, as compared to using a fixed-dose.<i>Approach.</i>Thirty-four healthy adult subjects (16 female, age = 25.0 ± 2.2 years, mean [range] weight = 66.90 [44.00, 97.52] kg) underwent slow Ferumoxytol infusion (<36 mg Fe min^-1) followed by unilateral brachial plexus MRN at 3.0T. Subjects were divided into three cohorts: variable dose (6%-26% of full 510 mg dose), fixed 25% dose (Cohort 2), and fixed 50% dose (Cohort 3). Signal intensities of nerve, artery, vein, and muscle were obtained via manual segmentation. Contrast ratios (CR) between vessel-muscle and nerve-muscle were compared between cohorts using two-sample<i>t</i>-tests. Regression analysis was performed between vessel-muscle CR and the Ferumoxytol dose calculated by mg, mg kg^-1, and mg l^-1. The doses required to achieve a target vessel-muscle CR of 0.2 were calculated.<i>Main results.</i>Cohort 3 had superior vascular suppression compared to Cohort 1 (i.e. lower vessel-muscle CR,<i>p</i>< 0.05). Higher correlations of vein-muscle CR with subject-specific dosing (<i>R</i>²= 0.396-0.409) were obtained than with absolute dose (<i>R</i>²= 0.341). Doses of 101.49 mg (17.81 mg-581.80 mg), 1.57 mg kg^-1(0.42 mg kg^-1-5.82 mg kg^-1), and 23.8 mg l^-1(5.88 mg l^-1-96.17 mg l^-1) were estimated to achieve the required diagnostic CRs of 0.2.<i>Significance.</i>Subject-specific Ferumoxytol dosing based on weight and estimated blood volume provided improved modeling and prediction of vascular suppression in brachial plexus MRN. This helps to optimize dose requirements, improve safety, while providing optimal vascular suppression needed for nerve visualization.