Enhanced ¹²⁹Xe T₁ relaxation in whole blood and in the presence of SPIONs at low magnetic field strengths

Abstract

To compare the effect of superparamagnetic iron oxide nanoparticles (SPIONs) on the T 1 of 129 Xe and 1 H and to measure the relaxation of 129 Xe in blood at low and high magnetic field strengths.Methods: 129 Xe and 1 H T 1 relaxometry was performed at low-and high-field strengths in samples containing different SPION concentrations, while imaging was used to compare the contrast obtainable in these two field regimes. In vivo experiments at variable field strengths were performed to determine the depolarization of 129 Xe in blood and the feasibility of in vivo dissolved-phase spectroscopy and imaging at low field. Results:The SPION relaxivity was substantially greater at low field for 1 H, increasing from 0.92 ± 0.06 mM s −1 at 11.7T to 31.5 ± 1.8 mM s −1 at 0.6 mT, and for 129 Xe, which increased from 0.13 ± 0.03 mM s −1 at 11.7T to 7.32 ± 0.71 mM s −1 at 2.1 mT. The additional MR signal loss increased from 0.7% at 9.4T to 20.6 ± 4.2% at 0.6 mT for 1 H and from −0.7 ± 3.4% at 9.4T to 12.7 ± 3.5% at 2.1 mT for 129 Xe. Blood was found to depolarize 129 Xe below 3T in a manner inversely proportional to the field strength. In vitro studies at 2.1 mT suggest 129 Xe relaxation times below 5 s in blood dilutions as low as 0.4% volume. Conclusion:SPIONs longitudinal relaxivity increases at low field both for 1 H and 129 Xe. The depolarization of xenon in blood, which is found to increase below 3T, effectively prevents in vivo dissolved-phase spectroscopy and imaging at low-field strengths.

High-Sensitivity, Low-Field 19F-MRI Approach Using High Manganese Ferrite Concentrations

“…As the magnetic strength decreases from 16.4 T to 0.1 T, the longitudinal relaxivity and the transverse relaxivity of multiple commercial gadolinium-based magnetic resonance contrast agents and experimental contrast agents significantly increase and decrease, respectively. − Hence, high-concentration contrast agents in 19 F-MRI at the low field will perform better than at the high field.…”

Absolute thermometry of human brown adipose tissue by magnetic resonance with laser polarized 129Xe

“…First, unlike in rodents where the HPXe gas can be provided continuously over the course of several minutes, enabling saturation of HPXe signal in distal tissues, in humans, HPXe gas is generally delivered via a single breath-hold, limiting the HPXe concentration in tissue, and thereby the achievable signal. Second, the longer blood transit time in humans is expected to lead to higher xenon depolarization, especially at clinical field strengths 43 . It is unclear whether the higher depolarization, coupled with the much smaller increase in BAT blood flow reported in humans during cold exposure 3 can still lead to a detectable lipid-dissolved 129 Xe signal in BAT for its detection by MR at clinical field strengths.…”