Magnetic nanoparticle relaxation measurement as a novel tool for in vivo diagnostics

A measurement system for spatially resolved relaxation measurements of magnetic nanoparticles (MNP) was developed and tested in regard to its applicability for in vivo diagnostics. The system is based on SQUID sensors to detect the magnetic relaxation of MNP and has been optimized to operate in a laboratory environment without any magnetic shielding. Due to a dead time between switching off the magnetizing field and starting the measurement only bound MNP with appropriate Neel relaxation times contribute to the measured signal. The detection limit of the system for MNP was found to be 0.3 nmol (17 ng) Fe. First investigations on the detection of MNP in mice after intravenous injection showed that the determination of their relaxing magnetization might have the potential to be used as a novel tool for medical imaging. (C) 2002 Elsevier Science B.V. All rights reserved.