Browsing by Subject "Magnetic resonance imaging"

Now showing 1 - 6 of 6
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    Altered Brain Responses to Noxious Dentoalveolar Stimuli in High-Impact Temporomandibular Disorder Pain Patients
    (2022-01) Peck, Connor
    High-impact temporomandibular disorder (TMD) pain may involve brain mechanisms related to central sensitization. We investigated brain responses to stimulation of trigeminal sites not typically associated with TMD pain by applying noxious dentoalveolar pressure to high- and low-impact TMD pain cases and pain-free controls during functional magnetic resonance imaging (fMRI). Fifty female participants were recruited and assigned to one of three groups based on the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) and Graded Chronic Pain Scale: controls (n=17), low-impact (n=17) and high-impact TMD (n=16). Multimodal whole-brain MRI was acquired following the Human Connectome Project protocol, including stimulus-evoked fMRI scans during which painful dentoalveolar pressure was applied to the buccal gingiva of participants. Group analyses were performed using non-parametric permutation tests for parcellated cortical and subcortical neuroimaging data. There were no significant between-group differences for brain activations/deactivations evoked by the noxious dentoalveolar pressure. For individual group mean activations/deactivations, a gradient in the number of parcels surviving thresholding was found according to the TMD pain grade, with the highest number seen in the high-impact group. Among the brain regions activated in chronic TMD pain groups were those previously implicated in sensory-discriminative and motivational-affective pain processing. These results suggest that dentoalveolar pressure pain evokes abnormal brain responses to sensory processing of noxious stimuli in high-impact TMD pain participants, which supports the presence of maladaptive brain plasticity in chronic TMD pain.
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    Intervertebral disc degeneration, quantified by T2* MRI, biochemistry, and compressive mechanics, correlated to global functional mechanics of the lumbar spine
    (2013-05) Ellingson, Arin Michael
    Low back pain is one of the most prevalent health complaints in the US, with an estimated 70-85% of the population developing back pain at some point in their life, creating a significant financial burden. Although the causes of low back pain are poorly defined and indistinct, most often implicated as the origin of pain, is the intervertebral disc. The disc affords the spine its extensive multidirectional motion due to the complex interaction between two morphologically, biomechanically, and biochemically distinct tissues: the annulus fibrosus and the nucleus pulposus. With advancing age, injury, pathology or a combination of these, a degenerative cascade of biomechanical, biochemical, and nutritional alterations diminish the discs' ability to maintain its structure and function. Unfortunately, measurement of these properties in vivo is currently not a viable option due to the invasiveness of the procedures. Therefore, an indirect method is needed to evaluate the multifarious characteristics of a patient's disc health. Of critical interest is the relationship that functional spinal mechanics has with the morphologic, biochemical, and biomechanical properties of the intervertebral disc as they change with degeneration. Eighteen osteoligamentous cadaveric lumbar spines that spanned the degenerative spectrum were utilized in a correlation study design to evaluate the relationships between each factors of disc health: imaging, biochemical content, biomechanical competency, and functional mechanics. Each specimen was first imaged using quantitative T2* MRI techniques, where the site-specific relaxation times and features of the Pfirrmann grading system, including signal intensity and distinction between the nucleus pulposus and surrounding annulus fibrosus, were measured. Then their functional spinal mechanics were evaluated and range of motion, neutral zone ratio, bending stiffness and helical axis patterns were computed. Local biochemical content and compressive biomechanical properties were subsequently analyzed. Each outcome measure was then assessed with respect to the others using correlation statistical methods in an effort to understand the multifactorial relationships surrounding disc degeneration. The T2* relaxation times and newly defined variables, T2* Intensity Area and Transition Zone Slope, were significantly correlated to the standard Pfirrmann grading, showing the T2* MR imaging parameters are sensitive to the morphological changes associated with disc degeneration. Also, these features enable the quantitative grading of disc degeneration without subjectivity or bias but with clinically recognized features of distinction. Furthermore, T2* relaxation times were found to have a high sensitivity for detecting the proteoglycan content of the intervertebral disc, which may potentially have a profound impact on the early diagnosis of degeneration. The T2* relaxation times were also significantly correlated to the residual stress and excised strain of the disc. These multi-faceted changes that occur with degeneration impact the global mechanics of the spinal unit by increasing the neutral zone to range of motion ratio, or joint instability, and altering the bending stiffness and range of motion. Even stronger correlations were measured with alterations in the helical axis patterns of lateral bending. There was a marked increase of out-of-plane rotations and a larger migration of the instantaneous axis of rotation with worsening degeneration evaluated by MRI, local biochemistry, and local residual mechanics. Quantitative T2* MRI has the sensitivity to predict the local biochemical and biomechanical properties of the intervertebral disc. Complementary to MRI analysis, the measurement of the pathway of motion throughout the degenerative progress, using the helical axis approach, can enhance the disc assessment. Altogether, these clinically viable methods may immediately improve the characterization of the intervertebral disc for enhanced treatment and care.
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    Investigation of Metamaterial Transmission line resonators for Ultra-High Field Magnetic Resonance Imaging RF Coils
    (2018-10) Panda, Vijayaraghavan
    The objective is to develop a highly efficient RF head coil on a thin substrate for the Ultra-high magnetic field (7 T and above) MRI systems. The artificial Metamaterial resonator is investigated for this purpose. Simulation and experimental results are provided for an 8-channel Metamaterial based RF coil in comparison with a standard high performance 8-channel dipole based RF coil for the 10.5 T MRI system. Each element is 180 mm (approximately a quarter of a wavelength λ0) long, identical, evenly spaced along the circumference of the cylindrical phantom, loaded with dielectric material, and referred to as inverted Metamaterial Zeroth Order Resonator. The resonator elements are open circuited, matched, and tuned to 447.06 MHz with the phantom. An unloaded to loaded quality factor ratio of 2.97 is obtained from the scattering matrix of the proposed design. The length independent nature of the proposed design and the flexibility of the lumped elements have provided an optimized element with a substrate thickness of roughly 3 mm (λ0/200). With the proposed design, a RF magnetic field strength (B1+) to √SAR ratio of 1.38 (compared to 1.46 for dipole) is obtained. Optimization of the physical design parameters, especially the distance between the element and the phantom, is performed to improve the transmission efficiency of the metamaterial based RF coil element. The amount of radiated power reaching 45 mm inside the phantom is used for the comparison. The optimal design for a 16 cm long, 7 T metamaterial resonator shows an increase of 1.1 dB and 3.2 dB in transmit power when compared to a dipole and microstrip element of same length. Similarly, the optimal design for an 18 cm long, 10.5 T metamaterial resonator shows an increase of 1.6 dB in power when compared to a 12 cm long microstrip and a 0.2 dB decrease in power when compared to an 18 cm long dipole. An electron band-gap (EBG) periodic structure is designed as the ground plane for the proposed metamaterial resonator. The simulation results show increased B1+ field magnitude when compared with the metamaterial resonator with a solid ground plane. Similarly, a technique of improving the surface current density by creating slots along the line is implemented in the 7 T microstrip resonator. The experimental results show an improved coil efficiency after including of the slots. The extendibility of the coil conductor length with the Metamaterial resonators is also shown by designing a 48 cm long, 10.5 T metamaterial loop body element (longer than a wavelength). Simulations and experimental results confirm the functionality of the loop element and show the comparison with a traditional loop element.
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    The Power of Rust and Sand at the Nanoscale: Iron Oxide and Mesoporous Silica Nanoparticles for Biomedical Applications
    (2015-08) Hurley, Katherine
    Due to their high surface area and size-dependent properties, nanoparticles have seen use as biomedical devices in the past several decades. Magnetic nanoparticles are of particular interest as their properties allow for a variety of uses including separations, targeting, imaging, and therapy. The biological milieu is not a pristine environment, however. The complex medium presents many challenges for particle stability and reproducible performance. It even makes fundamental particle characterization more difficult. In this thesis, magnetic iron oxide nanoparticles are investigated as biomedical devices which provide diagnosis/imaging and therapy (theranostics). Innovative methods for characterizing these particles and observing their behavior over time in biologically relevant environments are also presented. Overall, this thesis aims to make the important point that magnetic nanoparticles are not stagnant objects but are in fact dynamic systems capable of vast changes upon exposure to in vitro or in vivo environments. Aggregation, oxidation, and dissolution all play a role in real-world nanoparticle performance. To mitigate and control some of these concerns, a functionalized mesoporous silica shell is employed as a protective layer around the iron oxide nanoparticle cores. This protective shell causes resistance to each of the above-mentioned factors, resulting in more stable and predictable performance appropriate for treatment planning and biological use. In chapter one, various methods for the characterization of magnetic nanoparticles in biological matrices are reviewed. Several case studies are presented to demonstrate the necessity for complementary techniques to obtain a complete picture of nanoparticle transformations. In chapter two, an early-phase iron oxide/mesoporous silica core/shell nanoparticle is presented, and the effects of synthetic parameters and long term storage conditions on particle performance are examined. In chapter three, a commercially-available iron oxide nanoparticle is studied in detail in various biological environments to understand how particle heating and imaging properties are related and how aggregation can affect them. In chapter four, a functionalized mesoporous silica shell is applied to the iron oxide core from chapter three. The new core/shell particle demonstrates a substantial reduction in aggregation and thus a stabilization of material properties in vitro and in vivo. Finally, chapter five details a variety of transmission electron microscopy (TEM) studies with a focus on visualizing the nano/bio interface in vitro. Dark field TEM is presented as a useful tool for locating and differentiating inorganic nanoparticles, including but not limited to iron oxide nanoparticles, from biological structures or stain artifacts.
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    Segmentation-free measurement of cortical thickness from MRI
    (University of Minnesota. Institute for Mathematics and Its Applications, 2007-11) Aganj, Iman; Sapiro, Guillermo; Parikshak, Neelroop; Madsen, Sarah K.; Thompson, Paul M.
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    Segmentation-free measurement of cortical thickness from MRI by minimum line integrals
    (University of Minnesota. Institute for Mathematics and Its Applications, 2008-04) Aganj, Iman; Sapiro, Guillermo; Parikshak, Neelroop; Madsen, Sarah K.; Thompson, Paul M.