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 An optimized statistical approach to magnetic resonance image segmentation(Texas Tech University, 2001-08) Venkatesan, VikramThe usage of image segmentation techniques for the purpose of analysis of medical imagery is an essential facet in medical diagnosis. These techniques provide a potential Computer-Assisted Diagnostic (CAD) tool for today's medical industry. The aim of this research project is to use the DA algorithm for segmenting three main tissue classes from the MRI brain images in order to enable the human interpreter to recognize any abnormalities (such as lesions,) which have been enhanced by this procedure. DA is based on the minimization of a cost function that includes Shannon's Entropy in addition to the expected distortion. The mass-constrained version of the algorithm, as implemented here, successfully eliminates code-vector repetition, thus enabling faster convergence of the cost. The results indicate that lesion isolation in the case of simulated images requires further steps of pre- and post-processing of the source imagery. These methods successfully isolate the lesion areas in a specific case with confirmed MS in an advanced stage and show abnormalities in brain tissues for a suspected case. The analysis of the segmentation results indicates potential usage of DA in the area of medical image segmentation and also points towards future research and further improvement. In conclusion, the feasibility of this methodology to recognize MS lesions has been tested in this thesis, using both simulated and clinical MRI data.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 Multi-disciplinary study of lanthanide chelates as multi-modal molecular imaging agents(Texas Tech University, 2004-05) Manning, Henry CharlesMolecular imaging is a powerful tool that has the ability to elucidate biochemical mechanisms and signal the early onset of disease. Lanthanide chelates represent a unique class of molecular imaging agents that can yield multi-modal signatures including long-lived fluorescence and magnetic resonance. The primary aim of this dissertation is to demonstrate the utility of Lanthanide chelate molecular imaging agents for contrast enhanced disease demarcation. Traditionally, Lanthanide chelate imaging agents have been non-targeted perfusion agents that distribute in-vivo based on charge and lipophilicity. It is shown here that the structural features of the chelate can be modified to facilitate tunable spectroscopic and biodistribution properties in-vivo. While our perfusion-based agents have demonstrated considerable utility, their principal limitation is specificity. For increased specificity, we synthesized a trifunctional Lanthanide chelate that possessed an antenna for metal sensitization, phosphonate acid pendant arms for chelation, and a carboxylate arm for conjugation to targeting moieties such as antibodies, peptides, or small molecule ligands. Recently, peripheral benzodiazepine receptor (PBR) overexpression has been reported in many types of disease. Small molecule ligands of the PBR, such as PK11195, have been shown to bind with high affinity and thus could be used as contrast agent targeting moieties. Therefore, we synthesized a structural analogue of PK11195 that facilitates C-terminal conjugation. This form was then coupled to the trifunctional Lanthanide chelate and complexed with Europium and Gadolinium (Ln-PK11195). With the Ln-PK11195 agent in hand, it was demonstrated that PBR overexpressing C6 glioma cells would actively uptake the agent and that Ln-PK11195 seemed to be localizing on the PBR. Additionally, multi-modal imaging (fluorescence and MR) was shown possible on a single group of cells incubated with a Eu-PKl 1195 and Gd- PK11195 cocktail. Next, we demonstrated PBR profiling on surgically resected human tissue samples using Eu-PKl 1195, indicating a possible use as a histopathology stain. Both cancerous and non-cancerous PBR expressing disease was labeled with the agent. Finally, we fully characterized the primary spectroscopic signatures of Ln- PK11195 (time-resolved fluorescence and MR) for sensitivity to pH. It was shown that Ln-PK11195 demonstrates adequate pH sensitivity to measure localized, intracellular pH in tissues.Item Nuclear magnetic resonance force microscopy of ammonium dihydrogen phosphate and magnetism of cobalt nanocrystals(2005) Mirsaidov, Utkur; Markert, John T.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.Item 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 Synthesis of lanthanide chelates for biomedical imaging(Texas Tech University, 2003-12) Goebel, Timothy Stephen O'GaraLanthanide chelates are a somewhat unique class of molecules that have proven to be useful in the biomedical field as contrast agents for disease detection. This is due to many factors including their extremely large Stokes' shift, generally around 300 nm, and millisecond fluorescent lifetimes. The ability of these molecules to produce fluorescence in the low or zero-background regime as well as low cytotoxicity makes this class of molecules excellent candidates for use as contrast agents for a wide variety of applications in biological settings. Here we present the simple preparation and spectroscopic characterization of a new Europium chelate contrast agent, based on the 1, 4, 7, 10-tctraazacyclododecane macrocycle (cyclen). Eu-QF(CTME) produces a bright pinkish red luminescence when excited with low photon fluxes of UV light, indicating its potential for use in the field of biomedical imaging as a fluorescent probe. To determine the efficacy of this molecule as a fluorescent probe for disease detection, both animal testing as well as testing in a human tissue culture system was preformed. The well documented DMBA-treated Golden Hamster Cheek pouch epithelial cancer model was employed with Eu-QF(CTME) used as a topical agent for the detection of diseased tissue. In this preliminary study, the agent was observed to associate with malignant lesions, as well as dysplastic tissue. This suggests that Eu-QF(CTME) could be used as a contrast agent to aid in identifying oral precancer and cancer lesions. The results from the cell uptake experiments demonstrates the potential of this molecule as a stain for cancer cells.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.