International Journal on Magnetic Particle Imaging IJMPI
Vol. 12 No. 1 Suppl 1 (2026): Int J Mag Part Imag
https://doi.org/10.18416/IJMPI.2026.2603017

Proceedings Articles, ID 1017

The multi-color relaxation wall: fundamental limits of spectral separation in physics-based MPI

Main Article Content

Seungjun Oh (AI Convergence Department, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea), Hafiz Ashfaq Ahmad (AI Convergence Department, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea), Muhammad Umar Tahir (AI Convergence Department, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea), Jungwon Yoon (AI Convergence Department, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea)

Copyright (c) 2026 Seungjun Oh, Hafiz Ashfaq Ahmad, Muhammad Umar Tahir, Jungwon Yoon

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This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Multi-color Magnetic Particle Imaging (MPI) differentiates biological processes by exploiting particle-specific relaxation times, but conventional approaches require extensive calibration. We extend Sanders' physics-based framework with particle-specific Debye operators, enabling calibration-free multi-color reconstruction. Simulations with Momentum scanner parameters separate free-circulating (tau1 = 1 microsecond) and tissue-bound (tau2 = 20 microseconds) particles, achieving 95.9% and 78.4% purity and quantifying a frequency-domain trade-off: long-tau responses suffer attenuation when omega*tau >> 1, yielding approximately 15 dB difference at 45 kHz relative to short-tau particles. The formulation links tau-ratios to spectral separability (S = 0.375, rho = 0.625) and provides practical guidance for selecting particles and protocols without particle-specific calibration, applicable to preclinical and clinical MPI studies.

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