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POSTER TEMPLATE BY: www.PosterPresentations.com (nm) Neel Relaxation Brownian Relaxation Imaging by Magnetic Particles with a Nonlinear Field Response Gareth Kafka Adviser: Dr. Robert Brown Department of Physics, Case Western Reserve University, Cleveland, OH 44106 Motivation Tomographical imaging is essential in Biomedical fields. Magnetic Resonance Imaging is one such imaging technique, but it is plagued by large noise and requires large magnetic fields. Magnetic Particle Imaging (MPI) utilizes Superparamagnetic Iron Oxide (SPIO) particles with large magnetization responses. MPI thus provides potential for high signal to noise ratio and may have applicability in temporal applications, such as angiography and functional MPI. Introduction Relaxation Simulations Previous simulations assumed immediate particle responses. We modeled two relaxation mechanisms, Neel and Brownian. Neel relaxation is the relaxation of the magnetic moment of a single particle and is proportional to exp(K*d 3 ), where d is the particle diameter and K is a constant. Brownian relaxation is the randomization of magnetic moments with respect to each other and is proportional to d 3 . Previous results showed that larger particles had better resolution. We found that smaller particles had faster relaxation times. Consequently, there should be an optimal mid-sized particle. MPI Spectrometer An MPI spectrometer is being built to measure the best frequency response and efficacy of our SPIO sample. The apparatus schematic is shown above. We are using 8 nm sample particles. To saturate these particles, we built the transmit coil shown in Figure 6. The SPIOs are dissolved in a solution and placed in a container which fits inside the receive coil shown in Figure 7. This coil is then inserted into the transmit coil. Current and Future Work Acknowledgments/ References Currently, the Amplifier/Band Pass Filter Network shown in Figure 5 is being constructed. This network will have a band pass filter, an amplifier, and another band pass filter to generate the purest possible 25 kHz sine wave with a 1 A amplitude. Each of the inductors will be designed by wrapping wire in the shape of a toroid around a ferrite core. MPI uses the nonlinear response of SPIOs to magnetic fields to generate a signal. Signal is generated at a point where there is no field, the field free point (FFP). The FFP is moved around by several pairs of coils, as shown. Special thanks to: • Zhen Yao, CWRU Dept. of Physics • Yong Wu, CWRU Dept. of Physics • Lisa Bauer, CWRU Dept. of Physics • Dr. Mark Griswold, UH Dept. of Radiology • Matthew Riffe, UH Dept. of Radiology [1] B. Gleich and J. Weizenecker. “Tomographic Imaging Using the Nonlinear Response of Magnetic 25 kHz Sine Wave Input Amplifier/ Band Pass Filter Network Transmit Coil Receive Coil Band Stop Filter Data Collection Figure 1: The magnetization signal of SPIOs. On the top, an oscillating magnetic field is applied resulting in large harmonics. On the bottom, the oscillating field is offset by a constant value which damps out the signal [1]. Figure 2: MPI Apparatus. The drive field coils have currents running in the same direction; the selection field coils have currents running in the opposite directions [1]. Figure 3: Relaxation time vs particle size. The total relaxation time can be found from 1/τ Total = 1/ τ Neel + 1/τ Brownian . Bad Relaxation Effects Low Spatial Resolution Figure 4: Simulation Results. Blue indicates low SPIO concentration; red indicates large SPIO concentration. Relaxation causes blurring for large particles; poor spatial resolution causes blurring for small particles. Figure 6: Transmit coil. The coil is 2.9 cm long, has 430 turns, has an inner radius of 0.8 mm, and is made of 30 gauge wire. The magnetic field at the center of the coil is about 15 mT with an input current of 1 A. Figure 7: Receive coil. The coil is 1.45 cm long and had exactly enough coils to fill this length. It is made with 30 gauge wire. Figure 5: MPI Spectrometer apparatus. The input wave and two coils have been constructed. Avenues for Future Work Our simulations assumed a relaxation time dependent only on the particle size. The time constants could be modified to be field dependent as well. Simulations testing the temporal applications of MPI suggested in the Motivation section could be run. With the completion of the MPI spectrometer, the actual MPI apparatus could be built. Tests of different coil configurations, FFP trajectories, etc. could be conducted. Figure 8: Band Pass Filter Network. The inductors values will range from a few µH to a few mH, and the capacitors values will range from a few nF to a few µF.

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Imaging by Magnetic Particles with a Nonlinear Field Response Gareth Kafka Adviser: Dr. Robert Brown Department of Physics, Case Western Reserve University, Cleveland, OH 44106. Relaxation Simulations. MPI Spectrometer. Motivation. Current and Future Work. - PowerPoint PPT Presentation

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POSTER TEMPLATE BY:

www.PosterPresentations.com

(nm)

Neel RelaxationBrownian Relaxation

Imaging by Magnetic Particles with a Nonlinear Field ResponseGareth Kafka

Adviser: Dr. Robert BrownDepartment of Physics, Case Western Reserve University, Cleveland, OH 44106

MotivationTomographical imaging is essential in Biomedical fields. Magnetic Resonance Imaging is one such

imaging technique, but it is plagued by large noise and requires large magnetic fields.

Magnetic Particle Imaging (MPI) utilizes Superparamagnetic Iron Oxide (SPIO) particles with large magnetization responses. MPI thus provides

potential for high signal to noise ratio and may have applicability in temporal applications, such as

angiography and functional MPI.

Introduction

Relaxation SimulationsPrevious simulations assumed immediate particle

responses. We modeled two relaxation mechanisms, Neel and Brownian.

Neel relaxation is the relaxation of the magnetic moment of a single particle and is proportional to

exp(K*d3), where d is the particle diameter and K is a constant. Brownian relaxation is the randomization of magnetic moments with respect to each other and is

proportional to d3.

Previous results showed that larger particles had better resolution. We found that smaller particles had faster relaxation times. Consequently, there should be

an optimal mid-sized particle.

MPI Spectrometer

An MPI spectrometer is being built to measure the best frequency response and efficacy of our SPIO sample.

The apparatus schematic is shown above.

We are using 8 nm sample particles. To saturate these particles, we built the transmit coil shown in Figure 6. The SPIOs are dissolved in a solution and placed in a

container which fits inside the receive coil shown in Figure 7. This coil is then inserted into the transmit coil.

Current and Future Work

Acknowledgments/References

Currently, the Amplifier/Band Pass Filter Network shown in Figure 5 is being constructed. This network will have a band pass filter, an amplifier, and another

band pass filter to generate the purest possible 25 kHz sine wave with a 1 A amplitude. Each of the inductors will be designed by wrapping wire in the shape of a

toroid around a ferrite core.

MPI uses the nonlinear response of SPIOs to magnetic fields to generate a signal.

Signal is generated at a point where there is no field, the field free point (FFP). The FFP is moved around

by several pairs of coils, as shown.

Special thanks to:• Zhen Yao, CWRU Dept. of Physics• Yong Wu, CWRU Dept. of Physics• Lisa Bauer, CWRU Dept. of Physics• Dr. Mark Griswold, UH Dept. of Radiology• Matthew Riffe, UH Dept. of Radiology

[1] B. Gleich and J. Weizenecker. “Tomographic Imaging Using the Nonlinear Response of Magnetic Particles.” Nature, 435, pp. 1214-7, 2005.

25 kHz Sine Wave Input

Amplifier/Band Pass Filter Network

Transmit CoilReceive Coil

Band Stop Filter Data Collection

Figure 1: The magnetization signal of SPIOs. On the top, an oscillating magnetic field is applied resulting in large

harmonics. On the bottom, the oscillating field is offset by a constant value which damps out the signal [1].

Figure 2: MPI Apparatus. The drive field coils have currents running in the same direction; the selection field coils have

currents running in the opposite directions [1].

Figure 3: Relaxation time vs particle size. The total relaxation time can be found from 1/τTotal = 1/ τNeel + 1/τBrownian.

Bad Relaxation Effects Low Spatial Resolution

Figure 4: Simulation Results. Blue indicates low SPIO concentration; red indicates large SPIO concentration.

Relaxation causes blurring for large particles; poor spatial resolution causes blurring for small particles.

Figure 6: Transmit coil. The coil is 2.9 cm long, has 430 turns, has an inner radius of 0.8 mm, and is made of 30 gauge wire.

The magnetic field at the center of the coil is about 15 mT with an input current of 1 A.

Figure 7: Receive coil. The coil is 1.45 cm long and had exactly enough coils to fill this length. It is made with 30 gauge wire.

Figure 5: MPI Spectrometer apparatus. The input wave and two coils have been constructed.

Avenues for Future Work

Our simulations assumed a relaxation time dependent only on the particle size. The time constants could be

modified to be field dependent as well.

Simulations testing the temporal applications of MPI suggested in the Motivation section could be run.

With the completion of the MPI spectrometer, the actual MPI apparatus could be built. Tests of different

coil configurations, FFP trajectories, etc. could be conducted.

Figure 8: Band Pass Filter Network. The inductors values will range from a few µH to a few mH, and the capacitors values

will range from a few nF to a few µF.

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