Magnetic induction method aims at the noninvasive detection of liver iron overload by measuring the hepatic magnetic susceptibility. To solve the difficulty that eddy current effects interfere with the measurement of magnetic susceptibility, we proposed an improved coil system based on the static field magnetization principle in this study. We used a direct current excitation to eliminate the eddy current effect, and a rotary receiver coil to get the induced voltage. The magnetic field for a cylindrical object due to the magnetization effect was calculated and the relative change of maximum induced voltage was derived. The correlation between magnetic susceptibility of object and maximum magnetic flux, maximum induced voltage and relative change of maximum induced voltage of the receiver coil were obtained by simulation experiments, and the results were compared with those of the theory calculation. The contrast shows that the simulation results fit the theory results well, which proves our method can eliminate the eddy current effect effectively.
Magnetic susceptibility is an intrinsic physical quantity which describes the relationship between material magnetization and applied external magnetic field. Quantitative susceptibility mapping (QSM) is an MRI technology which can quantify the buck magnetic susceptibility of tissue in vivo. It is particularly effective at elucidating anatomy with paramagnetic or diamagnetic components. QSM technology is a method for solving the ill-pose problem of un-conventional de-convolution of the measured tissue magnetic field with the unit magnetic dipole field to obtain the susceptibility source map. Many multi orientation scan based QSM and clinically acceptable single orientation QSM methods have been proposed to solve this ill-posed problem. In this paper, the QSM concept is introduced and the various QSM methods are systematically categorized and discussed. The aim of this paper is to summarize the current research progress of QSM, popularize the knowledge of QSM and promote the improvements and the rational application of QSM in clinical field.