Browsing by Subject "SWIFT"

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    Determining optimum imaging parameters for SWIFT: application to superparamagnetic iron oxides and magnetized objects.
    (2011-06) O’Connell, Robert Daniel
    A relatively new pulse sequence in MRI known as SWIFT, sweep imaging with Fourier transformation, has been shown to effectively image spins with both short and long transverse and longitudinal relaxation rates. It is desirable to have equations that accurately describe the signal of spins when excited by SWIFT; however the Bloch equations are not easily solvable for the SWIFT sequence for all relaxation rates and flip angles. The purpose of this work is to determine a set of optimization equations for the SWIFT sequence through comparison to the Ernst energy equations via a Bloch simulator. An innovative contrast technique is also developed. The optimization equations are then tested experimentally and applied to imaging of superparamagnetic iron oxides. Susceptibility artifacts distort images around metal objects. In SWIFT images the susceptibility artifacts manifest as signal voids surrounded by pileup artifacts. This work develops predictive equations for the pileup artifacts around metallic spheres. A technique called ROC, radial off-resonance correction, is developed to reconstruct distorted images by utilizing the pileup predictive equations in post-processing.
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    Mri Detection Of Vertical Root Fractures In Endodontically Treated Teeth
    (2020-08) Groenke, Beth
    INTRODUCTION: Vertical root fracture (VRF) is known to occur in root canal treated (RCT) teeth and results in tooth loss. VRFs are difficult to diagnose. Magnetic Resonance Imaging (MRI) has the potential to identify VRF due to beneficial partial volume averaging, without using ionizing radiation. This investigation aims to compare the sensitivity and specificity of MRI versus cone-beam computed tomography (CBCT) in detecting VRF, using micro-computed tomography (microCT) as the reference standard. It also will describe the limits of MRI for detecting VRF. METHODS: 115 extracted human tooth roots were RCT using common techniques. VRFs were induced in a proportion that resulted in 62 VRF samples and 53 non-fractured control samples. All samples were imaged in a phantom using MRI and CBCT. Axial images for MRI and CBCT were presented to three board-certified endodontists. Evaluators determined VRF status and a confidence assessment for that decision. 30% of images were resampled to calculate intra- and inter-rater reliability. For MRI, the most coronal slice with discernible VRF was measured on correlated microCT to determine the minimum VRF width (µm). RESULTS: Sensitivity for MRI and CBCT were 0.66 (95%CI:0.53-0.78) and 0.58 (95%CI:0.45-0.70). Specificity was 0.72 (95%CI:0.58-0.83) and 0.87 (95%CI:0.75-0.95). Intra-rater reliability ranged from k=0.29-0.48 for MRI and k=0.30-0.44 for CBCT. Inter-rater reliability for MRI was k=0.37 and CBCT k=0.49. Median VRF width detected using MRI was 39µm (first quartile:20µm, third quartile: 58µm). CONCLUSION: MRI demonstrated ability to repeatedly detect VRF as small as 20 µm. There was no significant difference between sensitivity nor specificity for MRI versus CBCT in detecting VRF, despite the early stage of MRI development.