Improved sensitivity and limit-of-detection using a receive-only coil in magnetic particle imaging

Abstract

Magnetic particle imaging (MPI) is an imaging modality capable of quantitatively determining the 3D distribution of a magnetic nanoparticle (MNP) ensemble. In this work, we present a method for reducing the MNP limit of detection by employing a new receive-only coil (Rx-coil) for signal acquisition. The new signal detector is designed to improve the sensitivity and thus quality of reconstructed images. We present characterization measurements conducted with the prototype Rx-coil installed in a preclinical MPI scanner. The gradiometric design of the Rx-coil attenuates the unwanted signal contributions arising from the excitation field, leading to a 17 dB lower background level compared to the conventional dual-purpose coil (TxRx-coil), which is crucial for detecting low amounts of MNP. Network analyzer measurements of the frequency-dependent coil sensitivity, as well as spectral analysis of recorded MPI data demonstrate an overall increase of the coil sensitivity of about +12 dB for the Rx-coil. Comparisons of the sensitivity distributions revealed no significant degradations in terms of homogeneity for the Rx-coil compared to the TxRx-coil in an imaging volume of 6 × 3 × 3 cm. Finally, the limit of detection was determined experimentally for each coil type using a serial dilution of MNPs, resulting in values of 133 ng of iron for the conventional TxRx-coil and 20 ng for the new Rx-coil, using an acquisition time of 2 s. A linear relationship between the reconstructed signal intensities and the iron mass in the samples was observed with coefficients of determination (R) of above 99% in the range of the limit of detection to 3 10ng(Fe). These results open the way for improved image quality and faster acquisition time in pre-clinical MPI scanners.

Cellular uptake of magnetic nanoparticles imaged and quantified by magnetic particle imaging

“…The magnetic signal changes between these states are smaller compared to the changes between the free and the cell-bound state used in this proof-of-principle study. The prerequisite for the detectability of such small differences and thus the differentiability of the individual states is the further improvement of the MPI sensitivity, which could be achieved by advanced hardware components and background correction methods 33,38 . Additionally, the creation of such a SF matrix would complicate the image reconstruction from a mathematical point of view but could be adapted to the respective experimental research question.…”

“…By superimposing oscillating magnetic drive fields with field amplitudes of 12/12/12 mT and frequencies 24.5/26.0/25.3 kHz the FFP is moved on a Lissajous trajectory through the field of view (FOV) of size 40/40/20 mm. Based on these magnetic field settings and the nonlinear dynamic magnetic properties of MNPs, higher harmonics of the excitation frequencies are generated and measured by a gradiometric receive coil 33 . The spectral patterns of the MPI signal (u) depend on the MNP system, the environmental conditions and the spatial distribution of the MNPs within the FOV.…”

In vivo magnetic particle imaging: angiography of inferior vena cava and aorta in rats using newly developed multicore particles

“…Former theoretical modeling studies predicted picogram sensitivity with MPI-optimal MNP 20 . In vitro data suggest that a MPI sensitivity below 100 ng can be achieved 6,21 . The www.nature.com/scientificreports/ former studies on in vivo vascular MPI with a spatial resolution in the millimeter range were performed with MNP dosages above the applied dosage in our study 2 .…”

“…Imaging hardware and image reconstruction. Images were acquired in a preclinical 25/20 FF MPI scanner (Bruker Biospin/Philips, Germany) equipped with a separate receive-only gradiometer coil for increased sensitivity 6 . The acquisition was performed simultaneously with both the preinstalled coil and the separate receive coil.…”

“…The images depicted the large vessels including the vena cava and the cardiac chambers. Since then the heart and vena cava of mice have been repeatedly scanned with various MPI systems incorporating advances in MPI technology, such as X-space MPI 3 , traveling wave MPI (TWMPI) 4 , and the use of sophisticated separate receive coils 5,6 or in tracer development such as LS-008 particles 3,7 . These studies have shown improvements in angiographic image quality by improving sensitivity and resolution.…”