Fast iron oxide-induced low-field magnetic resonance imaging

Abstract

Dynamic images acquired by proton fast field-cycling magnetic resonance imaging are presented for the first time. Image contrast mediated by superparamagnetic iron oxide nanoparticles and weighted by the spin-lattice (T1) relaxation time, and both spin-lattice and spin-spin (T2) relaxation times, are discussed. Image acquisition and processing within 8 s is allowed for real-time recording of exemplary physical situations evolving in a compatible time-scale. Two simple examples are shown with the corresponding videos assembled by sequencing the acquired images. Fast iron oxide-induced low-field magnetic resonance imaging (MRI) constitutes the first step in the development of field-cycling functional MRI for biomedical and physical applications.

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

“…As seen in Figure 3 and Table 1, the T 1 of both 1 H and 129 Xe is shortened much more dramatically at low‐field strengths and the consequent r 1 values are much greater compared to the high‐field counterparts. The 1 H results agree with those reported previously, 37–39 where a large increase in 1 H longitudinal relaxation rates was reported in the presence of similar iron oxide nanoparticles in a range of fields below 250 mT. To the authors' knowledge, these are the first results demonstrating this effect also for 129 Xe spins.…”

“…36, Figure 4C), the effect seen here is consistent with what has been previously observed for similar SPION sizes at higher frequencies ranging from 10 kHz to 1 MHz (Ref. 37, Figure 2B). This is further supported by the agreement between our relaxivity values and those previously reported for 1 H at similar field strengths and for similar SPIONs 37,38 …”

“…This is further supported by the agreement between our relaxivity values and those previously reported for 1 H at similar field strengths and for similar SPIONs. 37,38 The increased image contrast seen at low field in Figures 4 and 5 is consistent with the measured increased longitudinal relaxivity at low field. Interestingly, while at high field the effect of SPIONs at the low concentration (2.5 μg/mL) used here is negligible, the same concentration of SPIONs at low field produced considerable signal reduction for both 1 H and 129 Xe spins.…”

“…Interestingly, while at high field the effect of SPIONs at the low concentration (2.5 μg/mL) used here is negligible, the same concentration of SPIONs at low field produced considerable signal reduction for both 1 H and 129 Xe spins. In fact, spectroscopy data show that a concentration of 5 μg/mL SPIONs dissolved in toluene would generate 50% 129 Xe signal reduction in just 5 s. It is also important to note that the SPION concentrations used here are 10-fold smaller than those used in previous 1 H studies (30-50 μg/mL), 36,37,39 meaning even greater image contrast could likely be achieved, especially at field strengths closer to 50 mT, where SNR comparable to that seen at 4.7T can be achieved. 15 Although this is well above the field strength used here, Ref.…”

“…37, Figure 2B). This is further supported by the agreement between our relaxivity values and those previously reported for 1 H at similar field strengths and for similar SPIONs 37,38 …”