Narrowband Magnetic Particle Imaging

UCSF/UC Berkeley Joint Graduate Group in Bioengineering, University of California, Berkeley, CA 94720, USA.
IEEE transactions on medical imaging 03/2009; 28(8):1231-7. DOI: 10.1109/TMI.2009.2013849
Source: PubMed


The magnetic particle imaging (MPI) method directly images the magnetization of super-paramagnetic iron oxide (SPIO) nanoparticles, which are contrast agents commonly used in magnetic resonance imaging (MRI). MPI, as originally envisioned, requires a high-bandwidth receiver coil and preamplifier, which are difficult to optimally noise match. This paper introduces Narrowband MPI, which dramatically reduces bandwidth requirements and increases the signal-to-noise ratio for a fixed specific absorption rate. We employ a two-tone excitation (called intermodulation) that can be tailored for a high-Q, narrowband receiver coil. We then demonstrate a new MPI instrument capable of full 3-D tomographic imaging of SPIO particles by imaging acrylic and tissue phantoms.

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    • "The idea of magnetic particle imaging (MPI) based on harmonic fields was first demonstrated in 2005 [20]. Various important achievements have been reported since that time including three dimensional realtime imaging [21], the use of intermodulation to create harmonics at frequencies other than multiples of the primary field [22] [23], xspace based imaging [24] [25], inclusion of a direct current (DC) field component to create even harmonics [26] [27], improvements in the magnetic characteristics of mNPs [28], the use of field free lines [29] [30] [31], a one-sided MPI system [32], an MPI system without a field free point [33], an alternative field free point [34], use in medical applications [21] [35] and a model-based imaging approach [36]. We previously introduced the susceptibility magnitude imaging (SMI) method that achieves mNP imaging with an array of drive coils, fluxgate magnetometers, and compensation coils using linear magnetic susceptibility measurements [37]. "
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    ABSTRACT: This study demonstrates a method for improving the resolution of susceptibility magnitude imaging (SMI) using spatial information that arises from the nonlinear magnetization characteristics of magnetic nanoparticles (mNPs). In this proof-of-concept study of nonlinear SMI, a pair of drive coils and several permanent magnets generate applied magnetic fields and a coil is used as a magnetic field sensor. Sinusoidal alternating current (AC) in the drive coils results in linear mNP magnetization responses at primary frequencies, and nonlinear responses at harmonic frequencies and intermodulation frequencies. The spatial information content of the nonlinear responses is evaluated by reconstructing tomographic images with sequentially increasing voxel counts using the combined linear and nonlinear data. Using the linear data alone it is not possible to accurately reconstruct more than 2 voxels with a pair of drive coils and a single sensor. However, nonlinear SMI is found to accurately reconstruct 12 voxels (R(2) = 0.99, CNR = 84.9) using the same physical configuration. Several time-multiplexing methods are then explored to determine if additional spatial information can be obtained by varying the amplitude, phase and frequency of the applied magnetic fields from the two drive coils. Asynchronous phase modulation, amplitude modulation, intermodulation phase modulation, and frequency modulation all resulted in accurate reconstruction of 6 voxels (R(2) > 0.9) indicating that time multiplexing is a valid approach to further increase the resolution of nonlinear SMI. The spatial information content of nonlinear mNP responses and the potential for resolution enhancement with time multiplexing demonstrate the concept and advantages of nonlinear SMI.
    Full-text · Article · Mar 2015 · Journal of Magnetism and Magnetic Materials
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    • "When an MNP is arranged as a delta function at the left end matrix point (i = 1), a field free point (FFP) [6,7] where the local magnetic field strength is almost zero is scanned in order (x = 1, 2, 3) while applying an alternative magnetic field at each FFP. Here, although such a procedure may be classified under the category of narrow band MPI [20], the FFP scanned by our method is encoded intermittently as in robot position movement [7]. Consequently, a series (Gi=1) that combines three waveforms of the induced EMF observed at each FFP is created. "
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    ABSTRACT: Background Molecular imaging using magnetic nanoparticles (MNPs)—magnetic particle imaging (MPI)—has attracted interest for the early diagnosis of cancer and cardiovascular disease. However, because a steep local magnetic field distribution is required to obtain a defined image, sophisticated hardware is required. Therefore, it is desirable to realize excellent image quality even with low-performance hardware. In this study, the spatial resolution of MPI was evaluated using an image reconstruction method based on the correlation information of the magnetization signal in a time domain and by applying MNP samples made from biocompatible ferucarbotran that have adjusted particle diameters. Methods The magnetization characteristics and particle diameters of four types of MNP samples made from ferucarbotran were evaluated. A numerical analysis based on our proposed method that calculates the image intensity from correlation information between the magnetization signal generated from MNPs and the system function was attempted, and the obtained image quality was compared with that using the prototype in terms of image resolution and image artifacts. Results MNP samples obtained by adjusting ferucarbotran showed superior properties to conventional ferucarbotran samples, and numerical analysis showed that the same image quality could be obtained using a gradient magnetic field generator with 0.6 times the performance. However, because image blurring was included theoretically by the proposed method, an algorithm will be required to improve performance. Conclusions MNP samples obtained by adjusting ferucarbotran showed magnetizing properties superior to conventional ferucarbotran samples, and by using such samples, comparable image quality (spatial resolution) could be obtained with a lower gradient magnetic field intensity.
    Full-text · Article · Jun 2013 · BMC Medical Imaging
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    • "Whilst its impedance Z = 10mΩ + jω 15µH is dominated by the inductance, it is the small resistance, to which the receive amplifier needs to be noise-matched. Narrow-band noise matching is straightforward and can give ultra-low noise performance at and very near to the design frequency [4]. However, the matching circuitry itself, with its additional reactive elements, drastically increases the noise figure at all other frequencies. "

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