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16 April 2012 Alternative spatial encoding for imaging magnetic nanoparticles
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Magnetic particle imaging (MPI) was introduced in 2005 and is one of the very few imaging methods capable of sensitivities that allow the term "molecular imaging" to be applied. Estimates of sensitivity allow nanograms of iron oxide nanoparticles to be imaged. MPI cyclically saturates the nanoparticles with an alternating magnetic field termed the drive field. The signal from the harmonics of the drive frequency is recorded. Localization is achieved by saturating the nanoparticles outside a "field free point." We present an alternative method of encoding the position of the magnetic nanoparticles. Signal is generated at the 2nd harmonic of the drive field only when a static magnetic field is present. Localization is achieved by placing a small static magnetic field gradient across the sample and the phase of the signal depends on the sign of the static field. The response of the nanoparticles at different static fields provides the localization. The localization can be modeled as a wavelet transform if the gradient is approximately linear. Smaller field gradients are required than in MPI. The sensitivity is potentially significantly higher than that of MPI; when minimum bandwidths are employed to achieve the maximum SNR, the SNR is 85% larger for new method. Variable resolution can be achieved. This is the first method capable of imaging the signal from a single harmonic independently of other harmonics. The new method has promise for low cost screening applications where only coarse localization might be required.
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John B. Weaver "Alternative spatial encoding for imaging magnetic nanoparticles", Proc. SPIE 8317, Medical Imaging 2012: Biomedical Applications in Molecular, Structural, and Functional Imaging, 83171W (16 April 2012); doi: 10.1117/12.913926;

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