AIP Advances最新文献

Magnetic particle imaging (MPI) is an emerging imaging modality that exploits the magnetization response of magnetic nanoparticle tracers. While MPI offers substantially higher resolution compared to magnetic resonance imaging, its translation to human-scale applications remains limited. These challenges stem from the requirement of high-intensity electric currents to generate strong magnetic fields, as well as reduced field uniformity with increasing coil spacing. To overcome these barriers, comprehensive simulation studies are essential for guiding MPI prototype design and performance optimization. In this work, we present a finite element method (FEM)-based design of a three-dimensional (3D) MPI prototype. The system integrates electromagnetic coils for the selection, drive, and focus fields, along with a gradiometer configuration for signal reception. Each coil's geometry and magnetic field were first simulated independently to validate its ability to generate the desired magnetic field and subsequently combined into a full-system design with time-domain input excitation signals. This framework achieved 3D field-free point (FFP) scanning within a 20 mm³ field of view. The selection field provided a gradient of 4, 2, and 2 T/m in z axis, y axis, and x axis, respectively, the drive field produced 20 mT, and the focus fields generated 40 mT (z-axis) and 20 mT (y-axis), enabling controlled spatial movement of the FFP. Overall, this study establishes a complete 3D FEM simulation framework for MPI system design and lays the foundation for future optimization toward clinical-scale applications.

Stretchable RF coils offer the potential to improve MRI performance by conforming closely to patient anatomy, regardless of patient size, thereby enhancing both signal-to-noise ratio (SNR) and patient comfort. In this work, we investigate a stretchable receive array design based on the coaxial capacitor (COCA) coil for 7 T MRI, constructed primarily from ultra-flexible Litz wire stitched onto elastic fabric substrates. The COCA coil eliminates the need for lumped capacitors and maintains stable decoupling performance under transverse stretching, provided that the overlapped area and the coil area change proportionally as the coil is stretched. Bench tests and phantom imaging experiments demonstrate that elliptical COCA coils (in the non-stretched state) maintain consistent decoupling characteristics across stretch ratios up to ×1.3 and outperform fixed arrays in SNR across varying phantom sizes. The proposed design shows strong potential for integration into wearable coil arrays, enabling improved imaging quality and adaptability for diverse patient anatomies.

This paper aims to examine the ability to control a model of red blood cell (RBC) dynamics and the associated extracellular flow patterns in microfluidic channels via oscillatory flows. Our computational approach employs a hybrid continuum-particle coupling, in which the cell membrane and cytosol fluid are modeled using the dissipative particle dynamics method. The blood plasma is modeled as an incompressible fluid via the immersed boundary method. This coupling is novel because it provides an accurate description of RBC dynamics while the extracellular flow patterns around the RBCs are also captured in detail. Our coupling methodology is validated with available experimental and computational data in the literature and shows excellent agreement. We explore the controlling regimes by varying the shape of the oscillatory flow waveform at the channel inlet. Our simulation results show that a host of RBC morphological dynamics emerges depending on the channel geometry, the incoming flow waveform, and the RBC initial location. Complex dynamics of RBC are induced by the flow waveform. Our results show that the RBC shape is strongly dependent on its initial location. Our results suggest that the controlling of oscillatory flows can be used to induce specific morphological shapes of RBCs and the surrounding fluid patterns in bio-engineering applications.

Plasmonic heating of gold nanoparticles (GNPs) using pulsed lasers (PLs) enables microbubble generation for imaging, diagnostics, and microfluidics. However, aggregation and photomodification cause inconsistencies (variations) in microbubble formation and distribution, particularly in pool-like environments where GNPs undergo aggregation and photomodification. This study experimentally investigates microbubble generation by heating GNPs (532 nm, nanoseconds PL) of various sizes and concentrations, using high-speed imaging (20 kfps). Results show unpredictable variations in bubble formation area (BFA), even under similar energy absorption. Large individual microbubbles were observed at relatively low energy absorption, primarily due to aggregation. Boiling on the transparent surface occurred in multiple tests, a phenomenon linked to optical pulling forces that deposited GNPs on the surface. This produced well-defined semi-circular bubbles (∼600 μm) within 50 μs. MB formation was more concentrated near the backward facing surface than along the laser beam, highlighting the role of optical pulling. Dissolved gas release influenced microbubble growth, particularly in samples prone to aggregation. In addition, prior laser pulses impacted BFA through photomodification and aggregation, sometimes reducing BFA despite higher energy absorption. This study provides new insights into the factors influencing microbubble formation and distribution in the plasmonic heating of GNPs. Understanding these mechanisms can help improve the reliability and efficiency of photothermal applications, enabling better control over plasmonic bubble generation for various scientific and technological advancements.