Contrast-agent phase effects: An experimental system for analysis of susceptibility, concentration, and bolus input function kinetics

A system is presented for experimental arterial input function (AIF) simulation and for accurate measurement of the concentration, susceptibility effects, and magnetic moment of paramagnetic MR contrast agents. Signal effects of contrast agents are evaluated with a stable, well-characterized, and precise experimental setup. A cylindrical phantom and a closed-loop circulating flow system were designed for AIF simulation, assessment of the physical determinants of contrast-agent phase effects, and measurement of contrast-agent properties under controlled conditions, A mathematical model of the AIF dynamics is proposed. From the experimental phase shift (Delta phi), either the concentration or molar susceptibility, chi(M), is determined. The linear dependence of Delta phi on concentration and echo time (TE), the orientation dependence, and the lack of dependence on T-1, T-2, and diffusion time are proven precisely for water solutions under a wide variety of conditions, The measured effective magnetic moment of Gd+3, mu(eff), was 7.924 +/- 0.015 Bohr magnetons in agreement with the theoretical value of 7.937.