Akshay Madan

Graduation Semester and Year

2013

Language

English

Document Type

Thesis

Degree Name

Master of Science in Biomedical Engineering

Department

Bioengineering

First Advisor

Changho Choi

Abstract

Proton (¹H) magnetic resonance spectroscopy (MRS) provides a non-invasive means of assessing metabolite concentration for a range of biologically important cerebral compounds in vivo. To extract quantitative information, additional data regarding proton spin relaxation phenomena is critical. Transverse relaxation times (T₂) of cellular metabolites depend on the local molecular environment in which they reside. Several neurological diseases alter the molecular environment, which may be reflected in the changes of the T₂ relaxation times. Therefore alterations in T₂ in tumors may provide important information about the local environment and a potential non-invasive diagnostic tool. Thirty-seven adult patients with gliomas and 11 healthy volunteers were enrolled in the study. The tumors comprised 22 low grade (grade II) and 15 high grade (grade III and grade IV) gliomas. Proton T₂ relaxation times of the MRS signals of total NAA (tNAA) (2.01 ppm), total creatine (tCr) (3.03 ppm), and total choline (tCho) (3.2 ppm), were measured in vivo at 3T. The T₂ relaxation time of lactate (at 1.3 ppm) was measured in the 7 glioma patients in which the signal was well detectable. Single voxel localized point resolved spectroscopy data were acquired at 8 echo times (TE's = 58, 88, 118, 148, 178, Proton (¹H) magnetic resonance spectroscopy (MRS) provides a non-invasive means of assessing metabolite concentration for a range of biologically important cerebral compounds in vivo. To extract quantitative information, additional data regarding proton spin relaxation phenomena is critical. Transverse relaxation times (T₂) of cellular metabolites depend on the local molecular environment in which they reside. Several neurological diseases alter the molecular environment, which may be reflected in the changes of the T₂ relaxation times. Therefore alterations in T₂ in tumors may provide important information about the local environment and a potential non-invasive diagnostic tool. Thirty-seven adult patients with gliomas and 11 healthy volunteers were enrolled in the study. The tumors comprised 22 low grade (grade II) and 15 high grade (grade III and grade IV) gliomas. Proton T₂ relaxation times of the MRS signals of total NAA (tNAA) (2.01 ppm), total creatine (tCr) (3.03 ppm), and total choline (tCho) (3.2 ppm), were measured in vivo at 3T. The T₂ relaxation time of lactate (at 1.3 ppm) was measured in the 7 glioma patients in which the signal was well detectable. Single voxel localized point resolved spectroscopy data were acquired at 8 echo times (TE's = 58, 88, 118, 148, 178, 208, 238, and 268 ms). T₂ was obtained with monoexponential fitting of metabolite signal estimates vs. TE's.The measured T₂ relaxation times of tCr and tCho were significantly different between tumor (171 ms and 297 ms respectively) and contra-lateral normal brain regions (152 ms and 244 ms respectively) but for tNAA (295 ms in tumors and 294 ms in contra-lateral normal brain) no significant difference was observed. For normal brain, low grade and high grade tumors, the mean tCr T₂ values were estimated to be 149 ± 8 ms, 165 ± 22 ms and 180 ± 32 ms, and the mean tCho T2 values were measured as 255 ± 29 ms, 291 ± 32 ms and 305 ± 58 ms respectively. The tCr and tCho T₂ values in low grade (p < 0.002 and p < 0.001 respectively) and high grade tumors (p < 0.0001 and p < 0.001 respectively) were significantly different than in normal brain, but the difference between low and high grades was not significant (p > 0.05). For tNAA the mean T₂ was estimated to be 286 ± 41 ms, 276 ± 33 ms and 247 ± 28 ms in normal brain, low grade and high grade tumors respectively. The tNAA T₂ was significantly different between high grade tumors and normal brain (p < 0.04) as well as between low grade and high grade tumors (p < 0.02). This study reports the T₂ of lactate in tumors for the first time, which was measured to be 256 ± 22 ms. Absolute quantification of lactate as well as tCr, tCho and tNAA was performed using the measured T₂ relaxation times.

Disciplines

Biomedical Engineering and Bioengineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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