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Proceedings Paper

The x-space formulation of magnetic particle imaging including non-negligible relaxation effects
Author(s): Laura R. Croft; Patrick Goodwill; Arbi Tamrazian; Kannan Krishnan; Steven Conolly
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Paper 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.

Paper Details

Date Published: 15 March 2011
PDF: 9 pages
Proc. SPIE 7965, Medical Imaging 2011: Biomedical Applications in Molecular, Structural, and Functional Imaging, 79652L (15 March 2011); doi: 10.1117/12.878418
Show Author Affiliations
Laura R. Croft, Univ. of California, Berkeley (United States)
Patrick Goodwill, Univ. of California, Berkeley (United States)
Arbi Tamrazian, Univ. of California, Berkeley (United States)
Kannan Krishnan, Univ. of Washington (United States)
Steven Conolly, Univ. of California, Berkeley (United States)

Published in SPIE Proceedings Vol. 7965:
Medical Imaging 2011: Biomedical Applications in Molecular, Structural, and Functional Imaging
John B. Weaver; Robert C. Molthen, Editor(s)

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