Chastity D. Shaffer-Whitaker

My Story:

Thesis title:
Evaluation of Hahn, CPMG, and combined spin echo analysis at 8 Tesla MRI

Abstract:
Magnetic Resonance Imaging is a non-invasive technique that has been developed for its excellent depiction of soft tissue contrasts. Instruments capable of ultra-high field strengths, 7 Tesla, were recently engineered and have resulted in higher signal-to-noise and higher resolution images. Total iron content within the brain is not homogenous. Age and a number of neurological conditions (such as Alzheimers, Parkinsons, Multiple Sclerosis, etc.) may influence the distribution. The ability to non-invasively detect the distribution of iron may be useful for diagnosis and for assessment of the effectiveness of treatments. Iron is also capable of indirectly influencing the signal in an MRI study by dephasing spins. This may then lead to an increase in relaxation rates. However, the standard transverse relaxation rate is not the most sensitive measure of iron content and other methods, such as gradient echo, are plagued with artifacts (example: air-tissue susceptibility signal loss and distortion). To increase the sensitivity of high field spin echo analysis to the distribution of iron content, we have analyzed Hahn and CPMG spin echoes with the Carr and Purcell spin echo signal equation. This resulted in an intrinsic T2 that describes the relaxation of the tissues and a susceptibility and diffusion dependent term (GD) that may be correlated with paramagnetic content. Experimentation includes the accuracy of Hahn, CPMG, and Combined Spin echo calculations in an inhomogeneous B1 field and the influence of macromolecular content on T2 and GD. We also examined Alzheimers disease using in vitro, in situ, and in vivo subjects with these techniques. Independent correlation to iron content is accomplished with ICP-Mass Spectroscopy. We found that reliable relaxation measurements are found within image regions of +/-20 degrees of a nominal 90 degrees flip angle. The paramagnetic content is linear with intrinsic T2 values quadratic with GD. Gradient and diffusion effects are not independent and a static regime model may be appropriate for describing GD. In vitro imaging of brain material results in similar relaxation rates to in situ imaging if the tissue is imaged immediately following autopsy. Magnetic Resonance Imaging is a non-invasive technique that has been developed for its excellent depiction of soft tissue contrasts. Instruments capable of ultra-high field strengths, 7 Tesla, were recently engineered and have resulted in higher signal-to-noise and higher resolution images. Total iron content within the brain is not homogenous. Age and a number of neurological conditions (such as Alzheimers, Parkinsons, Multiple Sclerosis, etc.) may influence the distribution. The ability to non-invasively detect the distribution of iron may be useful for diagnosis and for assessment of the effectiveness of treatments. Iron is also capable of indirectly influencing the signal in an MRI study by dephasing spins. This may then lead to an increase in relaxation rates. However, the standard transverse relaxation rate is not the most sensitive measure of iron content and other methods, such as gradient echo, are plagued with artifacts (example: air-tissue susceptibility signal loss and distortion). To increase the sensitivity of high field spin echo analysis to the distribution of iron content, we have analyzed Hahn and CPMG spin echoes with the Carr and Purcell spin echo signal equation. This resulted in an intrinsic T2 that describes the relaxation of the tissues and a susceptibility and diffusion dependent term (GD) that may be correlated with paramagnetic content. Experimentation includes the accuracy of Hahn, CPMG, and Combined Spin echo calculations in an inhomogeneous B1 field and the influence of macromolecular content on T2 and GD. We also examined Alzheimers disease using in vitro, in situ, and in vivo subjects with these techniques. Independent correlation to iron content is accomplished with ICP-Mass Spectroscopy. We found that reliable relaxation measurements are found within image regions of +/-20 degrees of a nominal 90 degrees flip angle. The paramagnetic content is linear with intrinsic T2 values quadratic with GD. Gradient and diffusion effects are not independent and a static regime model may be appropriate for describing GD. In vitro imaging of brain material results in similar relaxation rates to in situ imaging if the tissue is imaged immediately following autopsy.