Overcoming the Low Relaxivity of Gadofosveset at High Field with Spin Locking

The contrast agent gadofosveset, which binds reversibly to serum albumin, has a high longitudinal relaxivity at lower magnetic fields (≤3.0 T) but a much lower relaxivity at high fields. Spin locking is sensitive to macromolecular content; it is hypothesized that combining this technique with the albumin-binding properties of gadofosveset may enable increased relaxivity at high fields. In vitro measurements at 4.7 T found significantly higher spin-lock relaxation rates, R(1ρ) (1/T(1ρ)), when gadofosveset was serum albumin-bound than when unbound. R(1ρ) values for a nonbinding contrast agent (gadopentetate dimeglumine) in serum albumin were similar to those for unbound gadofosveset. R(2) (1/T(2)) values were also significantly higher at 4.7 T for serum albumin-bound gadofosveset than for unbound. Spin locking at high field generates significantly higher relaxation rates for gadofosveset than conventional contrast agents and may provide a method for differentiating free and bound molecules at these field strengths. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.