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Theses Doctoral

Sequence Development and Expansion of Zero J-Modulation Echo-Planar Chemical Shift Imaging in Three Dimensions (3D ZJ-EPSI)

Mojahed, Hamed

580,350 (35%) of 1,660,290 cancer patients are estimated to die in the US in 2013. Routine monitoring by X-Rays and CT scans are hazardous and evaluating this disease is time consuming. Magnetic Resonance Spectroscopy (MRS) has changed this mal-routine significantly in the past few years. MRS can help with better understanding of tumor pathology, study of tumor vascularization and progress, and having a predicting value for the treatment response and disease-free survival of the patients even before they start their treatment. Unfortunately, MRS is still not a common practice among the medical community because of three main reasons: First and far most is the fact that MRS acquisition is usually very time consuming. For a classic 1H 3D MRS with a spatial matrix of 20x18x10 with TR = 1000 ms, the scan time is about 1 hour which is "practically" impossible to acquire on a patient. Second, MR time is extremely expensive. Depending on the site, specific procedure, and strength of the magnet a simple MR study can cost somewhere between 1000 to 3500 US dollars. Finally, non-standardized MRS acquisitions and analysis protocols could create havoc in interpretation and usefulness of the technique. MRS scan parameters such as spatial resolution and echo times have been used non-uniformly in variety of different combinations in research and clinical studies. These parameters must be chosen with utmost care as they have direct impact on signal to noise ratio, quantification of the metabolites, and an overall interpretation of the results.
For the reasons said, having a method that could shorten the length of an MRS scan, reduce the cost, and potentially become a sensible routine in clinical practice is of a huge value. 3D Zero J-modulation Echo Planar Chemical Shift Imaging (3D ZJ-EPSI) is a fast MRS technique that can not only achieve all that was mentioned above, it can also provide additional detailed anatomical/pathological information due to its 3D nature. 3D ZJ-EPSI technique acquires proton magnetic resonance spectroscopy with time to acquisition (TE') of less than 1.7 ms and zero J-modulation effects. 3D ZJ-EPSI consisted of a slab excitation, followed by two phase encoding gradients and an echo planar switching readout gradient. The Free induction decay (FID) acquisition occurred during the plateaus of the switching gradient. The lipid suppression was achieved via ten Regional Saturation Technique (REST) pulses placed prior to the main slab excitation RF. The water suppression technique was a chemical shift selective (CHESS) pulse with RF-80º-80º-160º that was placed prior to lipid suppression pulses. The sequence was tested on a brain metabolite phantom with spatial resolution of 15×15×6 mm3 in 4:04 min, yielding spectra with comparable quality to the spectra obtained using conventional chemical shift imaging (CSI) technique taking 56:34 min. The sequence was also tested on human subjects with spatial resolution of 15×15×6 mm3 and 7.5×7.5×6 mm3 and the metabolic ratios were calculated and compared to literature values. Signals of coupled resonances were improved due to near zero TE' and zero J-modulation effects, while the macromolecules were more pronounced in the spectra. With non-water suppressed sequence, variations of waterline shape of different tissues in three spatial dimensions could be studied. The 3D ZJ-EPSI technique addresses the need for a fast MRS method that allows for a better quantification capability by acquiring proton spectra with zero J-modulation. The short acquisition time and near zero TE' make this methodology suitable for uniform quantification of metabolites in clinical studies.

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More About This Work

Academic Units
Biomedical Engineering
Thesis Advisors
Laine, Andrew F.
Degree
Ph.D., Columbia University
Published Here
June 4, 2013
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