Abstract
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, R1ρ (1/T1ρ), when gadofosveset was serum albumin-bound than when unbound. R1ρ values for a nonbinding contrast agent (gadopentetate dimeglumine) in serum albumin were similar to those for unbound gadofosveset. R2 (1/T2) 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.
Highlights
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
Most clinical scanners operate at 3 T or lower, where an improvetimes of these blank solutions led to poor model fits
The similarity of R1r values for gadofosveset in PBS and gadopentetate in BSA together with the observation of relatively large R1r values for gadofosveset in BSA all suggest, first, that the gadolinium has a greater effect on R1r than the mere presence of the macromolecule, and second, that it is the binding rather than any nonspecific interactions with the protein that has the largest effect on R1r
Summary
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. In vitro measurements at 4.7 T found significantly higher spin-lock relaxation rates, R1r (1/T1r), when gadofosveset was serum albumin-bound than when 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. VC 2011 Wiley Periodicals, Inc. The observed longitudinal relaxivity of gadofosveset (r1obs) includes contributions from both the bound and free molecules and is influenced by binding fraction and field strength. The large bound molecule has a lower tumbling rate and longer rotational correlation time [3], which facilitates a substantially (up to 10-fold) higher longitudinal relaxivity at low magnetic field strengths [4]. Absorption rate (SAR), at high B0 as SAR is proportional to the product of B20, B21L and the ratio of TSL to TR [10]
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