Single Harmonic-based Narrowband Magnetic Particle Imaging

Visualization of the in vivo spatial distribution of superparamagnetic iron oxide nanoparticles (SPIONs) is crucial to biomedicine. Magnetic particle imaging (MPI) is one of the most promising approaches for direct measurements of the SPION distribution. In this paper, we systematically investigate a single-harmonic-based narrowband MPI approach. Herein, only the 3rd harmonic at 15 kHz of the SPION signal induced in an excitation magnetic field of 5 kHz is measured via a narrowband detection system for imaging during scanning a field-free-point in a field of view. Experiments on spot and line phantoms are performed to evaluate the spatial distribution by the assessment of the full width at half maximum and modulation transfer function at different excitation magnetic fields from 4 to 10 mT. Experimental results demonstrate that reconstructed images have a spatial resolution of 1.6 and 1.5 mm for a gradient field of 2.2 T/m and 4.4 T/m in x- and z-direction, respectively, at an excitation magnetic field of 4 mT. In terms of line gap, two lines with a gap of 0.5 mm are resolved. With increasing the excitation magnetic field to 10 mT, the spatial resolution gets worse to 2.4 and 2.0 mm in x- and z-direction, respectively. Moreover, the custom-built MPI scanner allows a limit of detection of 53 microgram (Fe)/mL (500 ng Fe weight) using perimag SPIONs. In addition, the excellent performance is demonstrated by imaging experiments on an "emg" logo phantom. We believe that the proposed narrowband MPI approach is a promising approach for SPION imaging

Neural network image reconstruction for magnetic particle imaging

We investigate neural network image reconstruction for magnetic particle imaging. The network performance depends strongly on the convolution effects of the spectrum input data. The larger convolution effect appearing at a relatively smaller nanoparticle size obstructs the network training. The trained single-layer network reveals the weighting matrix consisted of a basis vector in the form of Chebyshev polynomials of the second kind. The weighting matrix corresponds to an inverse system matrix, where an incoherency of basis vectors due to a low convolution effects as well as a nonlinear activation function plays a crucial role in retrieving the matrix elements. Test images are well reconstructed through trained networks having an inverse kernel matrix. We also confirm that a multi-layer network with one hidden layer improves the performance. The architecture of a neural network overcoming the low incoherence of the inverse kernel through the classification property will become a better tool for image reconstruction.Comment: 9 pages, 11 figure

ROZWÓJ TOMOGRAFII NANOCZĄSTECZEK MAGNETYCZNYCH W ZAKŁADZIE ELEKTRONIKI JĄDROWEJ I MEDYCZNEJ

In this article summary of all accomplishments of Nuclear and Medical Electronics Division in the field of Magnetic Nanoparticles Imaging. Magnetic Nanoparticles Imaging is a new tomographic and molecular imaging method that employs superparamagnetic nanoparticles as the tracer. This article includes the most importuned definition regarding this technique, its most interesting features, as well as report about research conducted in the Division in prospect to advance this imaging method in Poland.Artykuł ten podsumowuje dotychczasowe osiągnięcia Zakładu Elektroniki Jądrowej i Medycznej w dziedzinie obrazowania nanocząsteczek magnetycznych. Obrazowanie nanocząsteczek magnetycznych jest to nowa metoda obrazowania molekularnego i tomograficznego wykorzystująca jako znacznik nanocząsteczki superparamagnetyczne. W treści artykułu zawarto najważniejsze definicje dotyczące tego zagadnienia. Obecny stan rozwoju tej techniki oraz jej najbardziej interesujące właściwości, jak również opis prac badawczych podjętych przez Zespół w celu rozwoju tej metody obrazowania w Polsce

Temperature-dependent magnetic particle imaging with multi-harmonic lock-in detection

Advances in instrumentation and tracer materials are still required to enable sensitive and accurate 3D temperature monitoring by magnetic particle imaging. We have developed a magnetic particle imaging instrument to observe temperature variations using MPI, and discuss resolution dependence on temperature and harmonic number. Furthermore, we present a low noise approach using lock-in detection for temperature measurement, and discuss implications for a new detection modality of MPI.Comment: 26 pages, 17 figure

Development of A Resonant Excitation Coil of AC Magnetometer for Evaluation of Magnetic Fluid

A high-homogeneity excitation coil with a resonant circuit for AC magnetometer is developed. A solenoid coil is designed to produce a high-homogeneity and strong excitation field using a resonant frequency method. The solenoid coil is fabricated with a Litz wire to suppress the increase of AC resistance due to the skin and proximity effects in the highfrequency region. The Litz wire is composed of 60 strands of copper wires with 0.1-mm diameter. The resonant frequency method is applied to cancel the reactance component by connecting the excitation coil with a capacitor in a series configuration. To enable excitation of the magnetic field at multiple frequencies, a resonant circuit consists of multiple values of resonant capacitors is constructed. The fabricated excitation coil showed a high homogeneity of the magnetic field and was able to maintain a constant resonant current up to 32.5 kHz

Single-sided magnetic nanoparticles imaging scanner for early detection of breast cancer

Electromagnetic coils form the basis of magnetic particle imaging (MPI) scanners. Previous scanner designs employ Helmholtz coil arrangement which has low sensitivity and high cost of fabrication. Furthermore, the scanners have long signal acquisition time and high memory requirement. This research focuses on developing a simple, low-cost and low memory demanding one-dimensional MPI scanner capable of imaging the position and concentration of magnetic nanoparticles (MNPs), using electromagnetic coils in the form of solenoids. The scanner produces an oscillatory magnetic field to excite the MNPs and a static magnetic field to confine the region of interest. The MNPs reacted with a nonlinear magnetisation response, inducing a voltage signal that was measured with an appropriate gradiometer pickup coil. In Fourier space, the received voltage signal consists of the fundamental excitation frequency and harmonics. This research utilises the second harmonic response of the MNPs to determine their position and concentration. Analogue Bandpass and Bandstop filters were designed for signal excitation and reception. Resovist and Perimag MNPs in liquid and immobilised form were used as tracer materials, which were moved to different spatial positions through the field of view (FOV), to record the induced voltages. The magnitude response of the Bandpass filter with 22.8 kHz fundamental frequency shows a flat amplitude in the passband with a smooth roll-off rate of ±80 dB/pole, while the Bandstop filter efficiently attenuates the fundamental frequency and passed the 45.6 kHz second harmonic frequency. Results of the excitation coil design revealed that a magnetic field within the range of 0.8 mT to 4.4 mT was obtained, while a voltage in microvolts range was induced in the gradiometer pickup coil. The contour maps derived from imaging one and two samples of the MNPs in the XY-plane revealed their position and shape. Additionally, the average threshold of the peak signal amplitude was obtained as 10.63 μV that would indicate the presence of MNPs concentration sufficient for cancer detection. The developed single-sided MPI scanner has a spatial resolution of less than 1 mm, a pixel resolution of 51.5 megapixels and 42.1 ms image acquisition time. Thus, the outcome of this research showed that the developed single-side MPI scanner has a potential in the detection of MNPs, which could help in sentinel lymph node biopsy for breast cancer diagnosis

A Soft Magnetic Core can Enhance Navigation Performance of Magnetic Nanoparticles in Targeted Drug Delivery

Magnetic nanoparticles (MNPs) are a promising candidate for use as carriers in drug delivery systems. A navigation system with real-time actuation and monitoring of MNPs is inevitably required for more precise targeting and diagnosis. In this paper, we propose a novel electromagnetic navigation system with a coil combined with a soft magnetic core. This system can be used for magnetic particle imaging (MPI) and electromagnetic actuator functions with a higher steering force and enhanced monitoring resolution. A soft magnetic core with coils can increase the magnetic gradient field. However, this also generates harmonic noise, which makes it difficult to acquire MNP monitoring signals with MPI. Therefore, the use of amplitude modulation magnetic particle imaging (AM MPI) is suggested. AM MPI uses a low-amplitude excitation field combined with a low-frequency drive field. Using this system, the measured signal becomes less sensitive to the soft magnetic core. Based on the new MPI scheme and the combination of the coil with the magnetic cores, the proposed navigation system can implement one-dimensional (1-D) MNP navigation and 2-D MPI. The proposed navigation system can shorten the 1-D guidance time by about 25% for MNPs in the size range of 45-60 nm and give an improved 2-D imaging resolution of 43%, compared with an air-coil structure

A Small Scale Magnetic Particle Relaxometer

Magnetic Particle Imaging (MPI) is a newly found imaging modality. It utilizes superparamagnetic materials as tracers in the blood stream to obtain very high resolutions. MPI promises to have high sensitivity, high spatial resolution and no radiation compared to other imaging modalities. Most commercially available MRI tracers (used for MPI for now) are all non-harmful when compared to Iodine (used for CT scan) and Gadolinium (used for MRI). MPI research is divided into three categories: MPI scanner development, superparamagnetic materials development, and image reconstruction techniques. In this project a small scale LabView-based system will be developed for use on small lab created phantoms, using 25 nm superparamagnetic iron oxide (SPIO) particles. At first a relaxometer will be developed, the imager will come as the next step. Transmitting and receiving signals will be implemented using LabView and a National Instruments PXI-1033 Chassis. Lab-built coils will be used to send the excitation signal and receive the signal induced by those SPIO’s. The objective of this project is to be introduced to a new imaging modality that can have various applications and at the same time considered safe. The system being built is considered inexpensive and shows most of the aspects of how magnetic particle imaging works, starting with the physical phenomena, superparamagnetic nanoparticle properties and relaxation, signal generation and acquisition, and an introduction to the hardware of MPI. The system can be used to introduce engineers and engineering students to the MPI physical phenomena