Background: Magnetic Particle Imaging is a novel method for medical imaging. It can be used to measure the\r\nlocal concentration of a tracer material based on iron oxide nanoparticles. While the resulting images show the\r\ndistribution of the tracer material in phantoms or anatomic structures of subjects under examination, no\r\ninformation about the tissue is being acquired. To expand Magnetic Particle Imaging into the detection of soft\r\ntissue properties, a new method is proposed, which detects acoustic emissions caused by magnetization changes\r\nin superparamagnetic iron oxide.\r\nMethods: Starting from an introduction to the theory of acoustically detected Magnetic Particle Imaging, a\r\ncomparison to magnetically detected Magnetic Particle Imaging is presented. Furthermore, an experimental\r\nsetup for the detection of acoustic emissions is described, which consists of the necessary field generating\r\ncomponents, i.e. coils and permanent magnets, as well as a calibrated microphone to perform the detection.\r\nResults: The estimated detection limit of acoustic Magnetic Particle Imaging is comparable to the detection limit\r\nof magnetic resonance imaging for iron oxide nanoparticles, whereas both are inferior to the theoretical detection\r\nlimit for magnetically detected Magnetic Particle Imaging. Sufficient data was acquired to perform a comparison to\r\nthe simulated data. The experimental results are in agreement with the simulations. The remaining differences can\r\nbe well explained.\r\nConclusions: It was possible to demonstrate the detection of acoustic emissions of magnetic tracer materials in\r\nMagnetic Particle Imaging. The processing of acoustic emission in addition to the tracer distribution acquired by\r\nmagnetic detection might allow for the extraction of mechanical tissue parameters. Such parameters, like for\r\nexample the velocity of sound and the attenuation caused by the tissue, might also be used to support and\r\nimprove ultrasound imaging. However, the method can also be used to perform imaging on its own.
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