Imaging of a superparamagnetic iron oxide nanoparticle distribution by a single-sided magnetic particle imaging scanner

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Magnetic Particle Imaging (MPI) is an emerging biomedical imaging modality designed to image distributions of superparamagnetic iron oxide nanoparticles (SPIONs) with high sensitivity1. In MPI, the continuous excitation of the SPION is provided by a sinusoidal magnetic field with rf frequencies. The spatial encoding of the signal is produced by selective saturating the SPION with a superimposed magnetic field gradient. Scanning the field-free region across the imaging volume senses the local concentration of SPION that allows a tomographic reconstruction of the tracer distribution inside the volume. SPIONs may serve as tumor markers2, which would allow the MPI device to be used for in vivo screening of cancer once translated to clinic.Several MPI devices have been developed but to date no translation to human has been done. Our single-sided field-free line (FFL) design, with the hardware to one side of the imaging volume, potentially enables nonrestrictive imaging in larger subjects, promoting utilities such as screening for cancer3. In our device, a selection field gradient is generated by a pair of co-planar elongated coils and an excitation magnetic field is generated by a single elongated drive coil4. The spatial encoding is provided by dynamical shifting the position of the FFL from altering the relative current between the two selection coils. Pertinent to this unilateral geometry the magnetic field profiles generated by the coils are inhomogeneous thus presenting a challenge to imaging. By implementing an algorithm of selection field compensation by applying a bias current to the drive coil we demonstrate that imaging can be performed. Here, we show the results from imaging simulations by means of specifically tailored filtered backprojection image reconstruction technique. In addition, we present first experimental results from 1D imaging of SPION phantoms (Fig.1) using ony moderate encoding field gradients thus providing proof of concept of our scanner.  Fig. 1: (a) Projection signal of SPION phantom (gradient of 0.42 T/m); (b) reconstructed image of a phantom using a single projection and knowledge of the phantom’s shape; (c) phantom of undiluted Synomag-D SPION (20 mm separation with 1.2 mm diameter).