The x-space formulation of magnetic particle imaging including non-negligible relaxation effects

Laura R. Croft; Patrick Goodwill; Arbi Tamrazian; Kannan Krishnan; Steven Conolly

doi:10.1117/12.878418

15 March 2011 The x-space formulation of magnetic particle imaging including non-negligible relaxation effects

Laura R. Croft, Patrick Goodwill, Arbi Tamrazian, Kannan Krishnan, Steven Conolly

Proceedings Volume 7965, Medical Imaging 2011: Biomedical Applications in Molecular, Structural, and Functional Imaging; 79652L (2011) https://doi.org/10.1117/12.878418
Event: SPIE Medical Imaging, 2011, Lake Buena Vista (Orlando), Florida, United States

Abstract

Magnetic particle imaging (MPI) is an emerging medical imaging modality that is predicted to have improved sensitivity and contrast as compared to existing technologies. MPI uses a strong magnetic field gradient (6.5 T/m) to spatially localize the induction response of ultra-small superparamagnetic iron oxide nanoparticles (USPIOs), which are currently approved as a contrast agent for MRI. This new imaging modality has excellent contrast and will be safe for human use. MPI relies on USPIO dipole moments aligning quickly with the applied magnetic field, but Neel and Brownian relaxation mechanisms can significantly retard this alignment. By causing this lag in magnetization alignment, relaxation ultimately degrades the resolution and accuracy of the MPI method. Our early simulation results indicate that relaxation effects in larger USPIOs could degrade spatial resolution by a factor of two or more. Our goal here is to develop a rigorous and predictive mathematical model for the imaging process including relaxation effects. The x-space formulation of MPI previously developed by our group details the theoretical signal, bandwidth, resolution, SNR, and SAR of MPI; however this theory was formulated assuming negligible relaxation times. Here we updated the x-space analysis of MPI to include relaxation effects and have demonstrated that this inclusion is essential for excellent agreement with experimental MPI data. We have also shown that relaxation degrades image resolution and accuracy, necessitating an improved understanding of relaxation for future mitigation of these consequences through careful USPIO and MPI system optimization.

Citation Download Citation

Laura R. Croft, Patrick Goodwill, Arbi Tamrazian, Kannan Krishnan, and Steven Conolly "The x-space formulation of magnetic particle imaging including non-negligible relaxation effects", Proc. SPIE 7965, Medical Imaging 2011: Biomedical Applications in Molecular, Structural, and Functional Imaging, 79652L (15 March 2011); https://doi.org/10.1117/12.878418

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