In vitro Gd-DTPA relaxometry studies in oxygenated venous human blood and aqueous solution at 3 and 7 T.

In vitro T(1) and T(2) (*) relaxivities (r(1) and r(2) (*) ) of Gd-DTPA (GaD) in oxygenated human venous blood (OVB) and aqueous solution (AS) at 3 and 7 T were calculated. GaD concentrations ([GaD]) in OVB and AS were prepared in the range 0-5 mM. All measurements were acquired at 37 ± 2 °C. At both 3 and 7 T, a linear relationship was observed between [GaD] and R(1) in both AS and OVB. At 7 T, r(1) in AS decreased by 7.5% (p = 0.045) while there was a negligible change in OVB. With respect to R(2) (*) , a linear relationship with [GaD] was only observed in AS, while a more complex relationship was observed in OVB; quadratic below and linear above 2 mM at both field strengths. There was a significant increase of over 4-fold in r(2) (*) with GaD in OVB at 7 T (for [GaD] above 2 mM, p <<0.01) as compared with 3 T. Furthermore, in comparison to r1 , r2 (*) in AS was less than 2-fold higher at both field strengths while in OVB it was ~20-fold and ~90-fold higher at 3 and 7 T, respectively. This observation emphasizes the importance of r(2) (*) knowledge at high magnetic fields, ≥3 T. The comparison between r(1) and r(2) (*) presented in this work is crucial in the design and optimization of high-field MRI studies making use of paramagnetic contrast agents. This is especially true in multiple compartment systems such as blood, where r(2) (*) dramatically increases while r1 remains relatively constant with increasing magnetic field strength.