Browsing by Subject "Magnetic resonance imaging"
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Item A 20-coil array system for high-throughput dynamic contrast-enhanced mouse MRI(2011-12) Ramirez, Marc Stephen; Bankson, James A.; Hazle, John D.MRI is a versatile tool for systematically assessing anatomical and functional changes in small animal models of human disease. Its noninvasive nature makes MRI an ideal candidate for longitudinal evaluation of disease progression in mice; however achieving the desired level of statistical power can be expensive in terms of imaging time. This is particularly true for cancer studies, where dynamic contrast-enhanced (DCE-) MRI, which involves the repeated acquisition of anatomical images before, during, and after the injection of a paramagnetic contrast agent, is used to monitor changes in tumor vasculature. A means of reducing the overall time required to scan multiple cohorts of animals in distinct experimental groups is therefore highly desirable. Multiple-mouse MRI, in which several animals are simultaneously scanned in a common MRI system, has been successfully used to improve study throughput. However, to best utilize the next generation of small-animal MRI systems that will be equipped with an increased number of receive channels, a paradigm shift from simultaneously scanning as many animals as possible to scanning a more manageable number, at a faster rate, must be considered. Given a small-animal MRI system with 16 available receive channels, the simulations described in this work explore the tradeoffs between the number of animals scanned at once and the number of array elements dedicated to each animal for maximizing throughput. An array system consisting of 15 receive and 5 transmit coils allows throughput-optimized acceleration of a DCE-MRI protocol by a combination of multi-animal and parallel imaging techniques. The array system was designed and fabricated for use on a 7.0-T / 30-cm MRI system, and tested for high-throughput imaging performance in phantoms. Results indicate that up to a nine-fold throughput improvement is possible without sacrificing image quality compared to standard single-animal imaging hardware. A DCE-MRI study throughput improvement of just over six times that achieved with conventional single-mouse imaging was realized. This system will lower the barriers for DCE-MRI in preclinical research and enable more thorough sampling of disease pathologies that progress rapidly over time.Item Design of portable CMOS NMR system(2021-05-06) Hong, Sungjin (Ph. D. in electrical and computer engineering); Pan, David Z.; Sun, Nan; Soenen, Eric; Orshansky, Michael E; Gharpurey, RanjitNuclear magnetic resonance (NMR) is the physical phenomenon that illustrates the behavior of the atomic nucleus under resonance condition. It has been an important tool for chemical spectroscopy. Recently, NMR spectroscopy becomes more popular with its wide variety of applications. Accordingly, the demand on the NMR spectrometers increases. However, the size and cost limit the widespread of the NMR spectroscopy. The limitations are resolved by miniaturization of the NMR spectrometers with CMOS chips and permanent magnets. Along with miniaturization, there are several problems arising from CMOS circuits and the magnets. This work addresses the existing problems in the portable NMR systems and proposes the circuit solutions. First, the portable NMR systems exploit the zero-intermediate frequency (IF) architecture by having the single frequency for sample excitation and local oscillator. From the architecture, the tradeoff between the inaccurate excitation and the 1/f noise is inevitable. This can be avoided by employing the separate frequencies with the IF frequency of 50 kHz. However, the dual-clock architecture randomizes the NMR output phase. The output with random phase disables the direct signal averaging. To solve this problem, the phase detection method by capturing the phase alignment of two clocks is proposed. The phase detector circuit triggers the on-chip timer that controls the NMR operation. This way, the output phase can remain constant. Second, the slow settling of the receiver deteriorates the acquisition sensitivity. This problem is solved with the proposed dynamic high-pass filter cutoff frequency switching technique. By doing so, the DC recovery time is 40 times faster than that without the technique, thereby achieving 10 µs of dead time. Lastly, the frequency fluctuation arises from large temperature coefficient of the permanent magnets. To calibrate the frequency variation, the frequency calibration method based on the signal peak detection is proposed. The peak detector extracts the amplitude of the NMR spin echoes which can be translated into the frequency response. The method exploits the natural behavior of the NMR signal whose amplitude is maximized at the frequency of interest. These techniques are combined with the fully integrated CMOS NMR transceiver. The proposed system demonstrates the one-dimensional (1D) NMR relaxation experiments for measuring T₂ relaxation time constant. The proposed features of fast receiver settling and high IF frequency allow the system to acquire the NMR signal that has the decaying time constant of less than 100 µs. Furthermore, NMR relaxation experiments are performed with the short time spacing between the refocusing pulses of 0.2 ms. The programmability and the high integration level extend the usage of the portable NMR system. The system with many circuit blocks such as delay-locked loop (DLL), timing controller, analog-to-digital converter (ADC), and the gradient controller allow various NMR experiments. The programmable NMR pulse sequence supports the two-dimensional (2D) experiments that characterize the two different physical properties of the sample. The inversion recovery method is employed to find the T₁ relaxation behavior, thereby producing the T₁-T₂ correlation of the samples. The system also demonstrates diffusion NMR experiments with the pulsed-field gradient. This diffusion information can be acquired with the on-chip gradient pulse sequencer and the supporting components such as the gradient coil, gradient amplifier, and the 3D-printed NMR probe.Item In vivo Ultrasound and Photoacoustic Monitoring of Mesenchymal Stem Cells Labeled with Gold Nanotracers(Public Library of Science, 2012-05-16) Nam, Seung Yun; Ricles, Laura M.; Suggs, Laura J.; Emelianov, Stanislav Y.Longitudinal monitoring of cells is required in order to understand the role of delivered stem cells in therapeutic neovascularization. However, there is not an imaging technique that is capable of quantitative, longitudinal assessment of stem cell behaviors with high spatial resolution and sufficient penetration depth. In this study, in vivo and in vitro experiments were performed to demonstrate the efficacy of ultrasound-guided photoacoustic (US/PA) imaging to monitor mesenchymal stem cells (MSCs) labeled with gold nanotracers (Au NTs). The Au NT labeled MSCs, injected intramuscularly in the lower limb of the Lewis rat, were detected and spatially resolved. Furthermore, our quantitative in vitro cell studies indicate that US/PA imaging is capable of high detection sensitivity (1×104 cells/mL) of the Au NT labeled MSCs. Finally, Au NT labeled MSCs captured in the PEGylated fibrin gel system were imaged in vivo, as well as in vitro, over a one week time period, suggesting that longitudinal cell tracking using US/PA imaging is possible. Overall, Au NT labeling of MSCs and US/PA imaging can be an alternative approach in stem cell imaging capable of noninvasive, sensitive, quantitative, longitudinal assessment of stem cell behaviors with high spatial and temporal resolutions at sufficient depths.Item Magnetic structure in manganites as probed by magnetic force microscopy(2005) Israel, Emil Casey; Lozanne, Alex deThis dissertation describes the use of magnetic force microscopy to directly measure the magnetic structure of a sample on a microscopic level. Our magnetic force microscope has been operated at temperatures ranging from 293 to 4.3 K and fields ranging from 0 to 3 T, providing a method for imaging temperature and field–dependent magnetic phase transitions and domain structures on a local scale. On the instrumentation side, I present details of the design, construction, and operation of a magnetic force microscope with coarse three dimensional tip/sample positioning. On the sample side, I focus primarily on the results of our studies concerning magnetic phase transitions in the manganite La1−x−yPryCaxMnO3, which for some dopings is a colossal magnetoresistive material. I will briefly discuss two ongoing projects: the use of our magnetic force microscope to image field–dependent domain structure in patterned magnetic manganite films and its use as an electrostatic force microscope.Item Nuclear magnetic resonance force microscopy of ammonium dihydrogen phosphate and magnetism of cobalt nanocrystals(2005) Mirsaidov, Utkur; Markert, John T.A Nuclear Magnetic Resonance Force Microscopy (NMR-FM) technique utilizing a somewhat uncommon experimental geometry has been developed. Characterization of external field effects on soft permalloy micromagnets on double torsional oscillators was performed. We showed that at high enough fields (above 1 Tesla), the quality factor for each mode is comparable to the zero field value. The changes in resonance frequency fit well with our model, and permitted high-sensitivity magnetic moment and magnetic anisotropy measurement. Effects of laser power on cantilevers used for NMR-FM has been studied in detail. The origins of the observed self-sustained oscillations has been addressed by our model. NMR-FM detection has been shown in an ammonium dihydrogen phosphate sample. Imaging and spin manipulation techniques were used for the first time to detect the nuclear spins in a sample with short relaxation times. A magnetic study of epitaxially grown cobalt nanocrystals on a Si(111) substrate has been performed. Enhancement of the magnetic moment and anisotropy energy have been observed and data are consistent with single domain model. Experimental evidence indicates small inter-nanocrystal interactions. Finally, future directions in achieving the single-spin detection limit is addressed.Item Nuclear magnetic resonance force microscopy: adiabaticity, external field effects, and demonstration of magnet-on-oscillator detection with sub-micron resolution(2003) Miller, Casey William; Markert, John T.Investigations of the adiabatic condition governing nuclear magnetic resonance force microscopy (NMR-FM) have been performed. It has been determined that the adiabatic conditional factor for protons in ammonium sulfate must have a value of 1.5 or greater to optimize the NMR-FM signal. A theoretical formalism is presented that describes the data. The characteristics of CoPt-capped single-crystal-silicon micro-oscillators with a magnetic field applied perpendicular to the magnetic film have been determined. The resonance frequency of the oscillators show two distinct regimes, one of softening and one of stiffening of the oscillator. A model is developed to describe the previously unseen softening. This work suggests that using NMR-FM with a magnetic particle on the oscillator is experimentally feasible. Magnet-on-oscillator NMR-FM has been demonstrated for the first time with our NMR-FM microscope using resonance slice thicknesses as small as ∼150 nm. The sample investigated was a semi-infinite slab of ammonium sulfate. The resonance slice of the microscope was scanned from vacuum into the sample by changing the tuned carrier frequency of the AC magnetic field H1. The resulting signal-to-noise ratio of ∼ 4 is slightly better than what was expected from conservative calculations. Finally, feasibility calculations and an experimental plan are set forth for the future measurement of relaxation times of single crystals of the superconductor magnesium diboride.Item Rest-activity rhythms and white matter microstructure across the lifespan(2020-08-07) McMahon, Megan Catherine; Schnyer, David M.The purpose of this study was to examine how rest-activity (RA) rhythm stability may be associated with white matter microstructure across the lifespan in healthy adults free of significant cardiovascular risk. We analyzed multi-shell diffusion tensor images from 103 healthy young and older adults using tract-based spatial statistics (TBSS) to examine relationships between white matter microstructure and RA rhythm stability. RA measures were computed using both cosinor and non-parametric methods derived from seven days of actigraphy data. Fractional anisotropy (FA) and mean diffusivity (MD) were examined in this analysis. Because prior studies have suggested that the corpus callosum (CC) is sensitive to sleep physiology and RA rhythms, we also conducted a focused region of interest analysis on the CC. Results indicated that greater rest-activity rhythm stability was associated with greater FA across both young and older adults, primarily in the corpus callosum and anterior corona radiata. This effect was not moderated by age group. Further, while RA measures were associated with sleep metrics, RA rhythm measures uniquely accounted for the variance in white matter integrity. This study strengthens existing evidence for a relationship between brain white matter structure and RA rhythm stability in the absence of confounding health risk factors. While there are differences in RA stability between young and older adults, the relationship with brain white matter appears to be stable across the lifespan. RA rhythms may be a useful biomarker of brain health across adult developmentItem Strongly correlated systems: magnetic measurements of magnesium diboride and group IV magnetic semiconductor alloys(2007-12) Guchhait, Samaresh, 1976-; Markert, John T.Nuclear Magnetic Resonance Force Microscopy (NMRFM) is a unique quantum microscopy technique, which combines the three-dimensional imaging capabilities of magnetic resonance imaging (MRI) with the high sensitivity and resolution of atomic force microscopy (AFM). It has potential applications in many different fields. This novel scanning probe instrument holds potential for atomic-scale resolution. MgB2 is a classic example of two-band superconductor. However, the behavior of these two bands below the superconducting transition temperature is not well understood yet. Also, the anisotropic relaxation times of single crystal MgB2 have not been measured because it is not yet possible to grow large enough MgB2 single crystals for conventional NMR. Using our homemade NMRFM probe, we have set out to measure the relaxation times of micron size MgB2 single crystals to anix swer several questions relating to the anisotropy, multiband behavior, and coherence effects in this unusual superconductor. The goal of a second project is to study the effects of doping on the critical current of MgB2 superconducting wires. Ti-sheathed MgB2 wires doped with nanosize crystalline-SiC up to a concentration of 15 wt% SiC have been fabricated, and the effects of the SiC doping on the critical current density (Jc) and other superconducting properties studied. In contrast with the previously reported results, our measurements show that SiC doping decreases Jc over almost the whole field range from 0 to 7.3 tesla at all temperatures. Furthermore, it is found that the degradation of Jc becomes stronger at higher SiC doping levels. Our results indicate that these negative effects on Jc could be attributed to the absence of significant effective pinning centers (mainly Mg2Si) due to the high chemical stability of the crystalline-SiC particles. The principle goal of a third project, the study of magnetic semiconductors, is to investigate magnetic properties of Mn-implanted GeC thin films. 20 keV energy Mn ions were implanted in two samples: 1) bulk Ge (100) and 2) a 250 nm thick epitaxial GeC film, grown on a Si (100) wafer by UHV chemical vapor deposition using a mixture of germane (GeH4) and methylgermane (CH3GeH3) gases. A SQUID magnetometer study shows granular ferromagnetism in both samples. While the Curie temperature for both samples is about 180 K, the in-plane saturated magnetic moment per unit area for the first sample is about 2.2×10−5 emu/cm2 and that for the second sample is about 3.0 × 10−5 emu/cm2 . The external field necessary to saturate the magnetic moment is also larger for the second sample. These results show clear enhancement of magnetic properties of the Mn-implanted GeC thin film over the identically implanted Ge layer due to the presence of a small amount of non-magnetic element carbon.Item Targetable PLGA microparticles and nanoparticles for the magnetic resonance imaging of atherosclerosis(2008-12) Doiron, Amber Lynn; Peppas, Nicholas A., 1948-Atherosclerosis is a chronic disease characterized by the formation of plaque in hemodynamically unstable regions of arteries. The disease involves complicated molecular and cellular processes including inflammation, the immune system, low density lipoprotein, cytokines, and many other components. As such, the degree of disease is difficult to determine, and the clinical outcomes that stem from the disease are hard to predict. Current imaging techniques lack specificity for the plaques likely to cause clinical consequences such as heart attack or stroke. Consequently, a new and molecularly selective contrast agent formulation is necessary for accurate imaging of plaque and to aid in the determination of the correct patient-specific treatment. To that end, a stealth biodegradable particle was designed containing a high payload of contrast agent that is targetable to specific states of plaque development. The core material used in creation of the particle was the FDA-approved poly(lactide-co-glycolide) (PLGA), with carboxylic acid termini. The polymer was used in a modified water-in-oil-in-oil double emulsion method to form particles of sizes ranging from approximately 50 nm to 20 [mu]m, of near‐spherical shape, and with smooth surfaces. The PLGA particles were loaded with up to 30% Gd-DTPA, an FDA-approved contrast agent used with magnetic resonance imaging (MRI). As an adjunct, to enable visualization of individual particles in vitro, particles were alternatively loaded with rhodamine 6G, a fluorescent agent. The PLGA particles were surface functionalized with poly(ethylene glycol) (PEG) with a primary amine end group. The acid group of the PLGA and PEG-linked amine were coupled through an amide bond using carbodiimide chemistry. The presence of PEG on the surface of particles was confirmed using electron microscopy, 1H NMR, and zeta potential. The other end of the PEG chain terminated in a carboxylic acid that was subsequently used for coupling to a monoclonal antibody against the cell surface markers of inflammation and atherosclerosis, vascular cell adhesion molecule‐1 (VCAM‐1) and intercellular adhesion molecule-1 (ICAM-1). Particles with conjugated antibodies successfully attached to, entered, and distributed throughout cells in vitro.