Browsing by Subject "Particle imaging"

Now showing 1 - 4 of 4

Open Access
A deep equilibrium technique for 3D MPI reconstruction
(Infinite Science Publishing, 2024-03-10) Güngör, Alper; Sarıtaş, Emine Ülkü; Çukur, Tolga
Image reconstruction in MPI involves estimation of the particle concentration given acquired data and system matrix (SM). As this is an ill-posed inverse problem, image quality depends heavily on the prior information used to improve problem conditioning. Recent learning-based priors show great promise for MPI reconstruction, but priors purely driven by image samples in training datasets can show limited reliability and generalization. Here, we propose 3DEQ-MPI, a new deep equilibrium technique for 3D MPI reconstruction. 3DEQ-MPI is based on an infinitely-unrolled network architecture that synergistically leverages a data-driven prior to learn attributes of MPI images and a physics-driven prior to enforce fidelity to acquired data based on the SM. 3DEQ-MPI is trained on a simulated dataset, and unlike common deep equilibrium models, it utilizes a Jacobian-free backpropagation algorithm for fast and stable convergence. Demonstrations on simulated data and experimental OpenMPI data clearly show the superior performance of 3DEQ-MPI against competing methods. © 2024 Güngör et al.; licensee Infinite Science Publishing GmbH.
Open Access
Design of a hybrid magnetic fluid hyperthermia and magnetic particle spectrometer setup
(Infinite Science Publishing, 2024-03-10) Altınay, Ali Hakan; Ütkür, Mustafa; Sarıtaş, Emine Ülkü
Magnetic particle imaging (MPI) enables cancer imaging via enhanced permeability and retention effect that causes magnetic nanoparticles (MNPs) to accumulate in cancerous tissue, or via determining the change in MNP signal due to increased viscosity in cancerous tissue. MPI can also enable localization of magnetic fluid hyperthermia (MFH) therapy to a targeted region to locally heat up the MNPs and cause the death of cancerous tissue. However, the heating should be kept under control so that the nearby healthy tissue is spared. Hybrid MFH-MPI systems have the potential to enable real-time non-invasive temperature monitoring for hyperthermia therapy via the relaxation response of MNPs. Here, we present the design and simulation results of a hybrid MFH and magnetic particle spectrometer (MPS) setup. This hybrid design is composed of three coaxial coils with gradiometric windings to minimize the mutual inductances among all three coils.
Open Access
Effects of pulse duration on magnetostimulation thresholds
(Wiley-Blackwell Publishing, Inc., 2015-06) Saritas, E. U.; Goodwill, P. W.; Conolly, S. M.
Purpose: Medical imaging techniques such as magnetic resonance imaging and magnetic particle imaging (MPI) utilize time-varying magnetic fields that are subject to magnetostimulation limits, which often limit the speed of the imaging process. Various human-subject experiments have studied the amplitude and frequency dependence of these thresholds for gradient or homogeneous magnetic fields. Another contributing factor was shown to be number of cycles in a magnetic pulse, where the thresholds decreased with longer pulses. The latter result was demonstrated on two subjects only, at a single frequency of 1.27 kHz. Hence, whether the observed effect was due to the number of cycles or due to the pulse duration was not specified. In addition, a gradient-type field was utilized; hence, whether the same phenomenon applies to homogeneous magnetic fields remained unknown. Here, the authors investigate the pulse duration dependence of magneto stimulation limits for a 20-fold range of frequencies using homogeneous magnetic fields, such as the ones used for the drive field in MPI. Methods: Magnetostimulation thresholds were measured in the arms of six healthy subjects (age: 27±5 yr). Each experiment comprised testing the thresholds at eight different pulse durations between 2 and 125 ms at a single frequency, which took approximately 3040 min/subject. A total of 34 experiments were performed at three different frequencies: 1.2, 5.7, and 25.5 kHz. A solenoid coil providing homogeneous magnetic field was used to induce stimulation, and the field amplitude was measured in real time. A pre-emphasis based pulse shaping method was employed to accurately control the pulse durations. Subjects reported stimulation via a mouse click whenever they felt a twitching/tingling sensation. A sigmoid function was fitted to the subject responses to find the threshold at a specific frequency and duration, and the whole procedure was repeated at all relevant frequencies and pulse durations. Results: The magnetostimulation limits decreased with increasing pulse duration (Tpulse). For Tpulse < 18 ms, the thresholds were significantly higher than at the longest pulse durations (p < 0.01, paired Wilcoxon signed-rank test). The normalized magnetostimulation threshold (BNorm) vs duration curve at all three frequencies agreed almost identically, indicating that the observed effect is independent of the operating frequency. At the shortest pulse duration (Tpulse ≈ 2 ms), the thresholds were approximately 24% higher than at the asymptotes. The thresholds decreased to within 4% of their asymptotic values for Tpulse > 20 ms. These trends were well characterized (R2 = 0.78) by a stretched exponential function given by BNorm = 1+αe?(Tpulse/β)γ, where the fitted parameters were α = 0.44, β = 4.32, and γ = 0.60. Conclusions: This work shows for the first time that the magnetostimulation thresholds decrease with increasing pulse duration, and that this effect is independent of the operating frequency. Normalized threshold vs duration trends are almost identical for a 20-fold range of frequencies: the thresholds are significantly higher at short pulse durations and settle to within 4% of their asymptotic values for durations longer than 20 ms. These results emphasize the importance of matching the human-subject experiments to the imaging conditions of a particular setup. Knowing the dependence of the safety limits to all contributing factors is critical for increasing the time-efficiency of imaging systems that utilize time-varying magnetic fields. © 2015 American Association of Physicists in Medicine.
Open Access
Preventing interference between saturation coil and receive coil in MPI
(Infinite Science Publishing, 2024-03-20) Kor, Ege; Arslan, Musa Tunç; Takrimi, Manouchehr; Sarıtaş, Emine Ülkü
In magnetic particle imaging (MPI), the signals received from magnetic nanoparticles (MNPs) are directly proportional to concentration. Hence, accumulation of MNPs in off-target organs may overpower the signal from actual regions-of-interest that contain MNPs at a smaller concentration. We previously proposed placing a saturation coil over the off-target organ to locally suppress its signal. However, the saturation coil caused a large interference signal on the receive coil, necessitating the acquisition of a separate baseline to determine the interference signal. In this work, we propose methods to prevent the interference between the saturation coil and the receive coil to enable localized signal suppression without the need for an additional baseline acquisition. © 2024 Kor et al.; licensee Infinite Science Publishing GmbH.