Calibration-Free Relaxation-Based Multi-Color Magnetic Particle Imaging

Abstract

Magnetic particle imaging (MPI) is a novel imaging modality with important potential applications, such as angiography, stem cell tracking, and cancer imaging. Recently, there have been efforts to increase the functionality of MPI via multi-color imaging methods that can distinguish the responses of different nanoparticles, or nanoparticles in different environmental conditions. The proposed techniques typically rely on extensive calibrations that capture the differences in the harmonic responses of the nanoparticles. In this paper, we propose a method to directly estimate the relaxation time constant of the nanoparticles from the MPI signal, which is then used to generate a multi-color relaxation map. The technique is based on the underlying mirror symmetry of the adiabatic MPI signal when the same region is scanned back and forth. We validate the proposed method via simulations, and via experiments on our in-house magnetic particle spectrometer setup at 10.8 kHz and our in-house MPI scanner at 9.7 kHz. Our results show that nanoparticles can be successfully distinguished with the proposed technique, without any calibration or prior knowledge about the nanoparticles.

Fully automated gridding reconstruction for non-Cartesian x-space magnetic particle imaging

“…In addition, this technique can enable x-space reconstruction of Lissajous data obtained from existing commercial MPI scanners, which may then facilitate the usage of other x-space-based techniques on those systems (e.g. relaxation-based color MPI (Muslu et al 2018)).…”

Relaxation-based color magnetic particle imaging for viscosity mapping

“…Recently, a few groups have focused on understanding and utilizing this behavior for color MPI, with the purpose of differentiating different nanoparticle types and/or chemical environments. [3][4][5] Color MPI techniques broaden MPI's capabilities to applications such as SPIO-labeled catheter tracking for vascular interventions, 6 or steering of the catheters during endoscopic procedures. 7,8 Color MPI studies can also be extended for functional imaging purposes to determine the binding state of the SPIOs, 9 or to understand signaling and transportation in tissues.…”

“…In this study, we demonstrate imaging results of relaxationbased color MPI for viscosity mapping. We base the color MPI experiments on our recently proposed relaxation time constant estimation technique, 5,19 briefly referred to as time constant (s, TAU) estimation via Recovery of Underlying mirror Symmetry (TAURUS). Comparing the results from our in-house MPI scanner tuned to three different drive field (DF) frequencies, we show that frequencies around 10 kHz provide one-to-one mapping between the estimated time constant and viscosity for multicore cluster Nanomag-MIP nanoparticles.…”

“…However, the actual MPI signal, s(t), loses this symmetry property due to relaxation induced blurring along the scanning direction. We have previously shown with our TAURUS technique that s can be directly estimated from s(t) as follows: 5,19 s ¼…”

“…The imaging experiments were performed on our in-house MPI scanner. 5,23 The selection field was generated using permanent disc-shaped magnets, resulting in (À4.8, 2.4, 2.4) T/m/l 0 gradients in (x, y, z) directions [see Fig. 1(b)].…”