Relaxivity of Ferumoxytol at 1.5 T and 3.0 T

Objectives The aim of this study was to determine the relaxation properties of ferumoxytol, an off-label alternative to gadolinium-based contrast agents, under physiological conditions at 1.5 T and 3.0 T. Materials and Methods Ferumoxytol was diluted in gradually increasing concentrations (0.26–4.2 mM) in saline, human plasma, and human whole blood. Magnetic resonance relaxometry was performed at 37°C at 1.5 T and 3.0 T. Longitudinal and transverse relaxation rate constants (R1, R2, R2*) were measured as a function of ferumoxytol concentration, and relaxivities (r1, r2, r2*) were calculated. Results A linear dependence of R1, R2, and R2* on ferumoxytol concentration was found in saline and plasma with lower R1 values at 3.0 T and similar R2 and R2* values at 1.5 T and 3.0 T (1.5 T: r1saline = 19.9 ± 2.3 s−1mM−1; r1plasma = 19.0 ± 1.7 s−1mM−1; r2saline = 60.8 ± 3.8 s−1mM−1; r2plasma = 64.9 ± 1.8 s−1mM−1; r2*saline = 60.4 ± 4.7 s−1mM−1; r2*plasma = 64.4 ± 2.5 s−1mM−1; 3.0 T: r1saline = 10.0 ± 0.3 s−1mM−1; r1plasma = 9.5 ± 0.2 s−1mM−1; r2saline = 62.3 ± 3.7 s−1mM−1; r2plasma = 65.2 ± 1.8 s−1mM−1; r2*saline = 57.0 ± 4.7 s−1mM−1; r2*plasma = 55.7 ± 4.4 s−1mM−1). The dependence of relaxation rates on concentration in blood was nonlinear. Formulas from second-order polynomial fittings of the relaxation rates were calculated to characterize the relationship between R1blood and R2 blood with ferumoxytol. Conclusions Ferumoxytol demonstrates strong longitudinal and transverse relaxivities. Awareness of the nonlinear relaxation behavior of ferumoxytol in blood is important for ferumoxytol-enhanced magnetic resonance imaging applications and for protocol optimization. Received for publication August 25, 2017; and accepted for publication, after revision, October 23, 2017. Conflicts of interest and sources of funding: This project received R&D grant support by the Departments of Radiology and Medical Physics, University of Wisconsin, as well as the NIH (K24 DK102595). Furthermore, the authors wish to acknowledge support from GE Healthcare and Bracco Diagnostics who provide research support to the University of Wisconsin. Author contributions: S.D.S. contributed to this work while at the University of Wisconsin–Madison. S.D.S. is currently an employee of Toshiba Medical Research Institute, USA. C.N.W. contributed to this work while at the University of Wisconsin–Madison. C.N.W. is currently an employee of Synaptive Medical, Canada. T.S. contributed to this work while at the University of Wisconsin–Madison. T.S. is currently an employee at the University Hospital Basel, Switzerland. Correspondence to: Gesine Knobloch, MD, Department of Radiology, School of Medicine and Public Health, Wisconsin Institute of Medical Research, University of Wisconsin, 1111 Highland Ave, Madison, WI 53705. E-mail: gknobloch@wisc.edu. Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.

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