Magnetic particle imaging: kinetics of the intravascular signal in vivo

Abstract

Background Magnetic particle imaging (MPI) uses magnetic fields to visualize superparamagnetic iron oxide nanoparticles (SPIO). Today, Resovist ® is still the reference SPIO for MPI. The objective of this study was to evaluate the in vivo blood half-life of two different types of Resovist (one from Bayer Pharma AG, and one from I’rom Pharmaceutical Co Ltd) in MPI. Methods A Resovist concentration of 50 μmol/kg was injected into the ear artery of ten New Zealand White rabbits. Five animals received Resovist distributed by I’rom Pharmaceutical Co Ltd and five received Resovist by Bayer Pharma AG. Blood samples were drawn before and directly after injection of Resovist, at 5, 10, and 15 minutes, and then every 15 minutes until 120 minutes after the injection. The MPI signal of the blood samples was evaluated using magnetic particle spectroscopy. Results The average decline of the blood MPI signal from the two distributions differed significantly ( P =0.0056). Resovist distributed by Bayer Pharma AG showed a slower decline of the MPI signal (39.7% after 5 minutes, 20.5% after 10 minutes, and 12.1% after 15 minutes) compared with Resovist produced by I’rom Pharmaceutical Co Ltd (20.4% after 5 minutes, 7.8% after 10 minutes, no signal above noise level after 15 minutes). Conclusion In MPI, the blood half-life of an SPIO tracer cannot be equalized to the blood half-life of its MPI signal. Resovist shows a very rapid decline of blood MPI signal and is thus not suitable as a long circulating tracer. For cardiovascular applications in MPI, it may be used as a bolus tracer.

Magnetic Particle Imaging (MPI): Experimental Quantification of Vascular Stenosis Using Stationary Stenosis Phantoms

“…a blood pool tracer [21, 22]. That is because Resovist is cleared quickly from the blood stream by liver and spleen.…”

“…This is especially true for larger particles and particle clusters, which contribute more to the MPI signal of Resovist than its smaller particles [23]. Data in mice using the very sensitive Magnetic Particle Spectroscopy (MPS) show that the signal of Resovist in blood drops below noise level after 15–30 minutes without even reaching a steady state first [22]. After 5 minutes, a maximum of 40% of the initial signal could be measured.…”

Intracellular dynamics of superparamagnetic iron oxide nanoparticles for magnetic particle imaging

“…[24] As such, MPI offers high image contrast (with negligible background signal from diamagnetic tissue), a signal linear with tracer concentration [25] and zero depth attenuation, and is safe as it uses no ionizing radiation, as compared with many other biomedical imaging methods. Additionally, a demonstrated high sensitivity (200 nm Fe) [26] and high temporal resolution [27] is achieved when optimized SPIONs of tailored size and size dispersity are used [28,29].…”

Tunable in vivo circulation characteristics of PEGylated MPI tracers

“…Specifically, increasing PEG molecular weight from 5 kDa to 20 kDa led to a near doubling in t 1/2 ; on the other hand, preliminary results suggest that around 18.8% PEG loading provided the longest t 1/2 (160 minutes) when using a 20 kDa PEG. For comparison, independent pharmacokinetic studies with Resovist nanoparticles reported less than 5 minutes of blood half-life [1,2]. …”