Abstract
Magnetic particle imaging (MPI) is beneficial for bioanalytical cellular imaging, due to its lack of both attenuation and background signal, but it typically requires a very high field gradient to achieve submillimeter resolution. The authors use the N\'eel relaxation response of the tracers to encode the coordinates of the field-free point (FFP) while magnetically scanning the phantom image under a low field gradient. This approach identifies the FFP steering frequencies and trajectory density as important parameters for refining the spatial resolution, and unlocks the possibility for noninvasive submillimeter imaging of cells or small-animal models.
Highlights
Magnetic particle imaging (MPI) is an imaging technique that locates and quantifies magnetic nanoparticles by inducing ac magnetic fields under dc field gradient [1]
The particles at the field-free point (FFP) than those from outside the FFP to visualize the spatial distribution of the particles while the FFP or the phantom is moved within the field of view (FOV) [5]
While the nonlinear field-dependent dynamic magnetization resulting in the harmonic responses is the fundamental property exploited by regular MPI, frequency-dependent magnetization enables the modulated MPI to use the linear response in the low-field regime
Summary
Magnetic particle imaging (MPI) is an imaging technique that locates and quantifies magnetic nanoparticles by inducing ac magnetic fields under dc field gradient [1]. The conventional strategy of increasing the spatial resolution is to optimize the excitation frequency and amplitude to obtain large harmonic responses of the tracers [28]. This scenario should anticipate side effects such as excessive cell heating and peripheral nerve stimulation [13,29, 30]. We highlight a small ratio of the low-to-high excitation frequency to increase the spatial resolution of the modulated MPI to compensate the low-field gradient. Since this scan setup will increase the acquisition time and the amount of recorded data significantly, we explore mainly the characteristics of the modulated MPI at an excitation frequency ratio of 2 kHz/1 MHz
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