Browsing by Subject "Nanoparticle relaxation"

Now showing 1 - 4 of 4

Open Access
Calibration-free relaxation-based multi-color magnetic particle imaging
(Institute of Electrical and Electronics Engineers, 2018) Muslu, Yavuz; Utkur, Mustafa; Demirel, Ömer Burak; Sarıtaş, Emine Ülkü
Magnetic particle imaging (MPI) is a novel imaging modality with important potential applications, such as angiography, stem cell tracking, and cancer imaging. Recently, there have been efforts to increase the functionality of MPI via multi-color imaging methods that can distinguish the responses of different nanoparticles, or nanoparticles in different environmental conditions. The proposed techniques typically rely on extensive calibrations that capture the differences in the harmonic responses of the nanoparticles. In this paper, we propose a method to directly estimate the relaxation time constant of the nanoparticles from the MPI signal, which is then used to generate a multi-color relaxation map. The technique is based on the underlying mirror symmetry of the adiabatic MPI signal when the same region is scanned back and forth. We validate the proposed method via simulations, and via experiments on our in-house magnetic particle spectrometer setup at 10.8 kHz and our in-house MPI scanner at 9.7 kHz. Our results show that nanoparticles can be successfully distinguished with the proposed technique, without any calibration or prior knowledge about the nanoparticles.
Open Access
Cancer imaging and treatment monitoring with color magnetic particle imaging
(2021-09) Ütkür, Mustafa
Magnetic particle imaging (MPI) is emerging as a highly promising non-invasive tomographic imaging modality for cancer research. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as imaging tracers in MPI. By exploiting the relaxation behavior of SPIONs, the capabilities of MPI can also be broadened to functional imaging applications that can distinguish different nanoparticles and/or environments. One of the important applications of functional MPI is viscosity mapping, since certain cancer types are shown to have increased cellular viscosity levels. MPI can potentially detect these cancerous tissues through estimating the viscosity levels of the tissue environment. Another important application area of MPI is temperature mapping, since SPIONs are also utilized in magnetic fluid hyperthermia (MFH) treatments and MPI enables localized application of MFH. To achieve accurate temperature estimations, however, one must also take into account the confounding effects of viscosity and temperature on the MPI signal. This dissertation studies relaxation-based viscosity and temperature mapping with MPI, covering the biologically relevant viscosity range (<5 mPa·s) and the therapeutically applicable temperature range (25-45!C). The characterization of the SPION relaxation response was performed on an in-house arbitrarywaveform magnetic particle spectrometer (MPS) setup, and the imaging experiments were performed on an in-house MPI scanner. Both the MPS setup and the MPI scanner were designed and developed as parts of this thesis. The effects of viscosity and temperature on relaxation time constant estimations were investigated, and the sensitivities of MPI to these functional parameters were determined at a wide range of operating points. The relaxation time constants, t’s, were estimated with a technique called TAURUS (TAU, t, estimation via Recovery of Underlying mirror Symmetry), which is based on a linear relaxation equation. Although the nonlinear relaxation behaviors of the SPIONs are highly dependent on the excitation field parameters, SPION type, and the hardware configuration, the results suggest that one-to-one relation between the estimated t and the targeted functional parameters (i.e., viscosity or temperature) can be obtained. According to these results, MPI can successfully map viscosity and temperature, with higher than 30%/mPa/s sensitivity for viscosity mapping and approximately 10%/!C sensitivity for temperature mapping, at 10 kHz drive field frequency. In addition, the results suggest that the simultaneous mapping of viscosity and temperature can be achieved by performing multiple measurements at different drive field frequencies and/or amplitudes. Overall, these findings show that hybrid MPI-MFH systems offer a promising approach for real-time monitored and localized thermal ablation treatment of cancer. The viscosity and temperature mapping capabilities of MPI via relaxation time constant estimation can provide feedback for high accuracy thermal dose adjustment to the cancerous tissues, thereby, increasing the efficacy of the treatment.
Open Access
Rapid relaxation-based color magnetic particle imaging
(2022-09) Arslan, Musa Tunç
Magnetic particle imaging (MPI) is a rapidly developing medical imaging modality that exploits the non-linear response of magnetic nanoparticles (MNPs). Color MPI widens the functionality of MPI, empowering it with the capability to distinguish different MNPs and/or MNP environments. The system function approach for color MPI relies on extensive calibrations that capture the differences in the harmonic responses of the MNPs. An alternative calibration-free x-space-based method called TAURUS (TAU estimation via Recovery of Underlying mirror Symmetry) estimates a map of the relaxation time constant, τ, by recovering the underlying mirror symmetry in the MPI signal. However, TAURUS requires a back and forth scanning of a given region, restricting its usage to slow trajectories with constant or piecewise constant focus fields (FFs). In this thesis, a novel technique is proposed to increase the performance of TAURUS and enable τ map estimation for rapid and multi-dimensional trajectories. The proposed technique is based on correcting the distortions on mirror symmetry induced by time-varying FFs. Simulations and experiments in an in-house MPI scanner demonstrates that the proposed method successfully estimates high-fidelity τ maps for rapid trajectories that provide orders of magnitude reduction in scanning time (over 300 fold for simulations and over 8 fold for experiments) while preserving the calibration-free property of TAURUS. Additionally, the proposed method can successfully map the effective relaxation time constants in a relatively wide field-of-view at frame rates exceeding 5 frames-per-second. This thesis presents the first simulation results demonstrating that the proposed method is capable of generating high fidelity and high frame-rate color MPI images in real time.
Open Access
Rapid TAURUS for relaxation-based color magnetic particle imaging
(Institute of Electrical and Electronics Engineers Inc., 2022-08-03) Aslan, M. Tunç; Özaslan, A. Alper; Kurt, S.; Muslu, Y.; Saritas, Emine Ulku
Magnetic particle imaging (MPI) is a rapidly developing medical imaging modality that exploits the non-linear response of magnetic nanoparticles (MNPs). Color MPI widens the functionality of MPI, empowering it with the capability to distinguish different MNPs and/or MNP environments. The system function approach for color MPI relies on extensive calibrations that capture the differences in the harmonic responses of the MNPs. An alternative calibration-free x-space-based method called TAURUS estimates a map of the relaxation time constant, τ , by recovering the underlying mirror symmetry in the MPI signal. However, TAURUS requires a back and forth scanning of a given region, restricting its usage to slow trajectories with constant or piecewise constant focus fields (FFs). In this work, we propose a novel technique to increase the performance of TAURUS and enable τ map estimation for rapid and multi-dimensional trajectories. The proposed technique is based on correcting the distortions on mirror symmetry induced by time-varying FFs. We demonstrate via simulations and experiments in our in-house MPI scanner that the proposed method successfully estimates high-fidelity τ maps for rapid trajectories that provide orders of magnitude reduction in scanning time (over 300 fold for simulations and over 8 fold for experiments) while preserving the calibration-free property of TAURUS.