Saryu Singh

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


In recent years, several techniques of volume-selective excitation for extracting signals from a chosen region in a large sample have appeared for various applications in magnetic resonance (MR). Most of these techniques suffer from, at least, the T{dollar}\sb2{dollar}-decay problem, which rules out their application for short T{dollar}\sb2{dollar} species. The remaining methods, while not suffering from the above limitation, are generally sensitive to errors in the radio frequency (rf) tip-angle and imperfections in rf profile, which cause inaccurate localization.;To overcome these problems, I have devised a new method for multi-dimensional spatial localization by accurate outer volume suppression. The method uses a series of selective rf pulses and a rotating gradient to saturate only the region outside the region(s) of interest (ROI), whose magnetization remains ideally unaffected during the localization. The magnetization within the ROI(s) is then interrogated with a readout pulse to acquire data. Suppression of the outer volume signal as well as signal loss from the ROI caused by rf imperfections are approximately estimated theoretically and compared against the measured values. The method virtually eliminates the tip-angle errors, greatly reduces the imperfections in rf profile, and thus increases the accuracy of localization.;Analytical methods are presented to design the rf pulses to localize one or more ROIs, whose shape and size can be tailored to match in vivo targets at arbitrary positions. Experimental results from a phantom and animal study using an MR imager demonstrate that ROIs of various shape and size (e.g. single or multiple cylindrical ROIs of circular, square, elliptical, etc., cross-section) at arbitrary positions within a 3D volume can be localized by suppressing ({dollar}>{dollar}99.9%) the magnetization of unwanted regions in 30-60 ms. Also shown are the efficacy of the method in suppressing flow and aliasing artifacts in MRI, and in acquiring spectral/relaxometric data from a ROI.;The technique is suitable for short T{dollar}\sb2{dollar} species, as it does not suffer from the T{dollar}\sb2{dollar}-decay problem. Most importantly, it can be implemented on any existing commercial MR scanner, as it does not require any special hardware. Because the method is accurate and versatile, it has many applications in MR.



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