Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N52: Biomagnetic Imaging and SensingFocus
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Sponsoring Units: GMED GMAG Chair: Stephen Russek, NIST Boulder; Samuel Oberdick Room: Room 308 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N52.00001: Micron-scale magnetic resonance imaging with dynamic nuclear polarization at 5 K Invited Speaker: Robert Tycko Spatial resolution in inductively-detected magnetic resonance imaging (MRI) is limited by the relatively low sensitivity of conventional nuclear magnetic resonance (NMR). At room temperature, isotropic resolution in three-dimensional (3D) 1H MRI better than about 3.0 μm has proven difficult to achieve, even with microcoils, optimized radio-frequency pulse sequences, paramagnetic doping, and long measurement times. In principle, NMR sensitivity and consequently MRI resolution can be improved greatly by operating at low temperatures, especially temperatures well below 100 K where large nuclear spin hyperpolarizations can be achieved by cross-effect dynamic nuclear polarization (DNP). At low temperatures, strong static dipole-dipole couplings among 1H nuclear spins broaden the NMR signals, potentially abrogating any sensitivity advantages. However, deleterious effects of 1H-1H dipole-dipole couplings can be largely overcome by pulsed spin-lock detection and by homonuclear decoupling through Lee-Goldburg irradiation. Results of recent experiments that demonstrate these principles will be described. In particular, in experiments at 28 K without DNP and 5 K with DNP, we have acquired 3D images of test samples with isotropic resolution of 2.8 μm and 1.7 μm, respectively. Likely avenues for further progress will also be discussed. With improvements in DNP dopants (a.k.a. "polarizing agents") and receiver electronics, isotropic resolution equal to 1.0 μm or less in 3D 1H MRI seems attainable for total sample volumes on the order of 105 μm3. Useful applications in imaging of single biological cells or cell clusters may then become possible. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N52.00002: Real-Time In Vivo Tracking of Biological and Biochemical Milieu Using Hyperpolarized Magnetic Resonance Biosensors Lloyd Lumata Dynamic nuclear polarization (DNP) via the dissolution is a physics-based technique that amplifies the liquid-state nuclear magnetic resonance (NMR) signals of a variety of nuclei to unprecedented values typically by >10,000-fold. Carbon-13 (gamma γ=10.7 MHz/T), a stable and NMR-active isotope of carbopn, is the foremost target for hyperpolarization due to its utility in metabolic and biochemical imaging as seen in a plethora of hyperpolarized 13C MR studies using 13C-pyruvate and other 13C-labeled metabolic tracers. Although less sensitive than 13C, 15N-labeled (γ=4.31 MHz/T) biosensors have also been reported in a select number of hyperpolarized (HP) MR studies. In this presentation, the physics and instrumental aspects of the hyperpolarized magnetic resonance technology will be discussed in addition to its application in real-time tracking of the biological and biochemical activities in cells and in vivo in cancer and other pathologies. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N52.00003: Analyzing mixed cell populations using aquaporin-1 as a genetically encoded reporter for Diffusion Weighted MRI and Monte Carlo Simulations Rochishnu Chowdhury A long-standing challenge in cancer biology is to develop methodologies for measuring tumor properties noninvasively in deep tissues. This challenge is addressed by integrating Monte Carlo simulations with genetic reporters for magnetic resonance imaging(MRI). This approach revolves around a water channel called aquaporin-1(AQP1), which our lab introduced as a novel genetically encoded reporter for examining cells using MRI. AQP1-expressing cells exchange water faster than control cells, thereby showing increased water diffusion, which can be measured and imaged with diffusion-weighted MRI. The net increase in diffusion is affected by various parameters comprising cell-size, volume fraction of AQP1-labeled cells relative to unlabeled cells (the latter obstructing free diffusion), and their spatial arrangement. To use AQP1 as a noninvasive reporter for cell tracking in tissues, it is imperative to first solve the inverse problem connecting diffusion (measured with MRI) with the above-mentioned cell parameters. As a first step, we are trying to understand the relationship between diffusion changes to cell parameters in mixed cell populations of AQP1-labeled cells and unlabeled cells via live cell MRI and Monte Carlo simulations. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N52.00004: Nuclear Magnetic Resonance Force Microscopy Experiments for Single-Pulse T1 and Real-Space Spin Diffusion Imaging Peter W Kampschroeder, Yawer B Sagar, Devan Shoemaker, Justin Skweres, John T Markert We report the design and operation of a Nuclear Magnetic Resonance Force Microscopy (NMRFM) probe for studying 1H resonance in room-temperature liquids, varying T1 with CuSO4 paramagnetic ions. We use contained aqueous samples protected from high vacuum of order 10-6 torr, at which our cantilever quality factors are ~1000-3000, providing a force sensitivity of order 10-15 N. Single-pulse T1 measurements of 50 - 500 ms are obtained during an NMRFM cyclic inversion pulse by monitoring the decay of the spin magnetization during our typically 100 - 300 ms long adiabatic inversion pulse.Spin diffusion information is obtained by first exciting the spins in an ~2 μm resonant slice. We then scan to detect the spin magnetization changing with time over a 10μm long region of sample, and we use that spatial dependence to determine diffusion coefficients. |
Wednesday, March 8, 2023 12:42PM - 1:18PM |
N52.00005: Unambiguous MRI Contrast with Magnetic Nanoparticles: "Color" Contrast at High Field and Positive Contrast at Low Field Invited Speaker: Samuel D Oberdick Magnetic nanoparticles (MNPs) are typically thought of as negative contrast agents for magnetic resonance imaging (MRI). During an MRI scan, water protons situated nearby the strong magnetic field gradients of MNPs rapidly dephase, leading to decreased signal and dark contrast. Despite the loss in signal, MNP labels with negative contrast have been used for many applications, from clinical liver imaging to cellular MRI tracking. However, these methods have inherent ambiguity because negative contrast can be confused with magnetic susceptibility artifacts, such as air bubbles. MNPs are not strictly limited to negative contrast, though. In this talk, I will describe new pathways to realize unambiguous MNP labels using “color” contrast at high fields and positive contrast at low magnetic fields. First, I will describe how specially shaped MNP-polymer microparticles can be used as RF-addressable, “color” MRI contrast agents at high magnetic fields (9.4 T). These microparticles can generate a spectral shift 1000x larger than familiar NMR chemical shifts, providing an RF-identifier that is spectrally distinct from the environment. I will also show that the particles can be made of environmentally sensitive “smart” polymers for use as biosensors. Secondly, I will describe possibilities for using MNPs as positive contrast agents with low field MRI (LF-MRI). While MNPs can be used as positive contrast agents for clinical and high field MRI, the MNPs need to be specially synthesized with sizes of 3 nm or smaller. Here, I will discuss using FDA-approved contrast agents, like Ferumoxytol, as well as commercially available iron oxide MNPs with sizes of 5 nm – 16 nm for positive contrast at low field. LF-MRI scanners require less infrastructure than clinical MRI scanners and can be wheeled next to a patient’s bedside, creating revolutionary possibilities for point-of-care diagnostics. I will present experiments using an FDA-approved, 64 mT MRI scanner to evaluate the potential of MNPs as contrast agents for LF-MRI. At 64 mT, MNPs show enhanced longitudinal relaxivity (r1) and reduced transverse relaxivity (r2) compared to 3 T. Moreover, MNPs have a size-dependent r1 that is up to 8x larger than a common Gd-based contrast agent (Gd-BOPTA), suggesting that MNPs may outperform traditional positive contrast agents at lower fields. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N52.00006: Dynamics of magnetic nanoparticle assemblies in magnetic particle imaging Thinh Q Bui, Samuel D Oberdick, Frank M Abel, Adam Biacchi, Eduardo L Correa, Klaus N Quelhas, Mark-Alexander Henn, Weston L Tew, Angela R Hight Walker, Cindi L Dennis, Michael J Donahue, Solomon I Woods Magnetic nanoparticles (MNPs) are becoming increasingly important as tracers for non-invasive, in vivo magnetic particle imaging (MPI1), magnetic hyperthermia2, and thermometry3. For these applications, MNP tracers are driven by AC magnetic fields and detected by their modulated magnetic moments. Iron oxide nanoparticles with strong dipolar interactions exhibit enhanced MPI performance due to rapid magnetization reversal along strongly coupled chains of MNPs4. The chaining and magnetization dynamics span broad timescales and are governed by a complex set of parameters, including magnetic field amplitude, frequency, and temperature. We are using magnetic and physical characterization to investigate a number of strongly interacting iron oxide nanoparticle systems synthesized by our group. Here, we present mechanistic characterization using time-resolved magnetometry and electron microscopy for our synthesized ferrite iron oxide nanoparticles over a range of temperatures (275-320 K), magnetic field amplitudes (1-20 mTRMS), and timescales (20 ns to 10 seconds) to elucidate chaining dynamics. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N52.00007: Colloidal Nanomagnets Developed with Strong Liquid-Phase AC Field Response for Remote 3D Imaging and Thermometry Adam Biacchi, Thinh Q Bui, Frank M Abel, Eduardo L Correa, Samuel D Oberdick, Curt A Richter, Cindi L Dennis, Solomon I Woods, Angela R Hight Walker Colloidal nanomagnets (CNMs) are an exciting class of material being investigated for use in a host of remote therapeutic and diagnostic modalities such as magnetic particle imaging and hyperthermia.1 These applications exploit the unique soft magnetic properties that manifest when the size of these crystals is confined to the nanoscale, specifically a strong response to applied alternating current (AC) magnetic fields while simultaneously remaining dispersed in liquid media. CNMs, which are often solution-synthesized ferrites, also frequently display a temperature-dependent magnetization that may be employed for thermometry. Here, we unveil a series of CNMs specifically developed for use in AC magnetic field-based remote imaging and thermometry. Careful selection of the synthetic reagents and precursor thermal decomposition kinetics2 allow for control of the resultant CNM composition (Fe, Co, Zn, V ratios) and size (5-80 nm). By tuning these variables, as confirmed by spectroscopy, scattering, and microscopy, we can then use frequency-, amplitude-, and temperature-dependent magnetometry to reveal their commensurate AC field response. In this way, we correlate CNM structure to performance and conclude by expounding guidelines to govern our use of CNMs for magnetic imaging and thermometry. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N52.00008: Investigation of Soft Magnetic Material Cores in Transcranial Magnetic Stimulation Coils and the Effect of Changing Core Shapes on the Induced Electric Field in Small Animals Mohannad Tashli, Ravi L Hadimani, George Weistroffer, Aryan Mhaskar, Deepak Kumbhare, Mark S Baron Transcranial magnetic stimulation (TMS) is a safe, effective and non-invasive treatment for several psychiatric and neurological disorders. Lately, there has been a surge in research utilizing this novel technology in treating other neurological and psychiatric ailments. The application of TMS on several neurological disorders requires the induced electric and magnetic fields to be focused and targeted to a small region in the brain. TMS of a focal cortical territory will ensure modulation of specific brain circuitry without affecting unwanted surrounding regions. This can be achieved by altering the properties of the magnetic core material used for the TMS system. In this study, soft ferromagnetic materials having high permeability, high saturation magnetization and low coercivity have been investigated as TMS coil cores in finite element simulations. Also, magnetic field measurements have been carried out using different cores in the TMS coil. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N52.00009: High-speed, sensitive NV-diamond magnetic imager for microscopic biomagnetism Jiashen Tang, Zechuan Yin, Tao Tao, Connor A Hart, Jennifer M Schloss, Matthew J Turner, John W Blanchard, Ronald L Walsworth Diamond-based optical magnetometry using nitrogen-vacancy (NV) defect centers is uniquely positioned to detect micrometer-scale biomagnetic fields, enabling applications in neuroscience, NMR and rare-cell detection. Developing an NV magnetometer with high-speed, sensitive, and wide-field imaging capability is a crucial step towards mapping of dynamic magnetic fields from transient local neuronal activities. Leveraging recent Ramsey-based imaging protocols, which has enhanced sensitivity, bandwidth, and uniformity compared to conventional continuous-wave optically detected magnetic resonance (CW-ODMR) method, we present a high-sensitivity, broadband magnetic imager capable of resolving sub-millisecond-scale temporal magnetic dynamics with improved robustness to experimental imperfections. We characterize the trade-offs among spatial resolution, bandwidth and minimal detectable field, and discuss near-term imaging applications in neuronal and other cellular-level magnetism. We further suggest potential avenues to improve SNR and detect ever smaller magnetic fields. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N52.00010: Tracking the Effect of Deuterated Water on Glycolysis in Cancer Cells Using 13C Nuclear Magnetic Resonance Cody Larsen, Lloyd Lumata Deuterated water (D2O) is a form of water composed of the hydrogen isotope deuterium, with a natural abundance of 0.015% in most natural sources. Increasing or depleting the amount of D2O present in water has been found to cause severe cytotoxicity in cultured cells and mice. This work seeks to investigate the effect that D2O has on the metabolic pathways of cultured neuroblastoma and glioblastoma cells, specifically regarding its impact on glucose metabolism and lactate production via glycolysis. Cell culture media with varying amounts of D2O were fabricated and administered to cells, and the resultant impact upon glucose metabolism and the proliferation of the cells were observed. The metabolic pathways were tracked via 13C Nuclear Magnetic Resonance (NMR) spectroscopy through the conversion of 1-13C-Glucose to Lactate over 48 hours using a Bruker 600MHz NMR spectrometer. The results of these experiments will be presented along with explanations of the biological pathways explored and microscopic techniques employed. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N52.00011: Two Dimensional Imaging Using a Single-Sided Field Free Line Magnetic Particle Scanner Christopher P McDonough, Alexey A Tonyushkin Magnetic Particle Imaging (MPI) is a promising tracer-based preclinical biomedical imaging modality, which could be used for detection and treatment of cancer. The images created in MPI consist solely of hot spots of a tracer without background, which is similar to images from PET and SPECT. In MPI superparamagnetic iron oxide nanoparticles (SPIONs) are excited by an AC magnetic field and the signal detected by a receive coil. For spatial encoding a gradient magnetic field is applied, which creates a field free region (FFR). At the location of the FFR the SPIOs are maximally sensitive to the excitation, moving the FFR allows sampling the local concentration of SPIOs in region of interest. A major challenge currently in MPI is scaling up a scanner to a human size making MPI clinically useful. Construction of a full body closed bore scanner has been shown impractical due to high power consumption. An alternative solution is the single-sided scanner's geometry providing an unrestricted access to the imaging volume. Our group is developing a single-sided scanner, which uses a field free line as an FFR promising higher sensitivity and more robust image reconstruction techniques. In this work we demonstrate the first 2D imaging of various phantoms as a proof of principle of our design. |
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