MAGNETIC RESONANCE IN MEDICINE 23,96-108
(1992)
Spatially Localized in Vivo 'H Magnetic Resonance Spectroscopy of an Intracerebral Rat Glioma' BRIAND. Ross,*HELLMUT MERKLE,KRISTY HENDRICH, R. SCOTT STAEWEN. AND MICHAELGARWOOD Department of Radiology, University of Minnesota, Minneapolis, Minnesota 55455 Received April 25, 1990; revised September 24, 1990 Surface coil MRI combined with spatially localized spectroscopy was used to noninvasively detect 'H signals from metabolites within an intracerebral malignant glioma in rats. The MRS pulse sequence was based upon two-dimensional ISIS, which restricted 'H signals to a column-shaped volume, combined with onedimensional spectroscopic imaging, which further resolved the signals into 8 or 16 slices along the major axis of the column. All experiments were executed with adiabatic pulses which induced uniform spin excitation despite the inhomogeneous radiofrequency field distribution produced by the surface coil transmitter. Surface coil MRI and MRS experiments were performed on phantom samples, normal rat brains, and rat brains harboring malignant gliomas. Spatially resolved in vivo 'H spectra of intracerebral gliomas revealed significantly decreased concentrations of Nacetyl-aspartate and creatine and increased lactic acid (or lipids) as compared to the contralateral hemisphere. These results demonstrate that metabolic abnormalities in intracerebral rat gliomas can be spatially resolved in a noninvasive manner using localized in vivo 'H MRS. 0 1992 Academic Press, Inc. INTRODUCTION
Magnetic resonance spectroscopy ( MRS ) provides a powerful means to noninvasively detect metabolites in living tissues. The application of MRS to the study of tumor metabolism is currently an active area of research due to its potential utility in diagnosis and in the evaluation of treatment protocols (e.g., see Ref. ( I , 2 ) ) .Recently, interest in 'H MRS of brain tumors has increased since preliminary measurements of brain tumors have revealed significant differences in metabolite levels between histologically different tumors (e.g., benign vs malignant gliomas), as well as between different subsets of the same tumors (3-5). It can be argued that metabolic abnormalities and efficacy of therapies can best be studied using animal models since it is possible to control many of the variables affecting tumor initiation and progression. Although subcutaneous tumors in rodents are the most common tumor models used for in vivo MRS studies ( 6 ) ,a limited number of intracerebral brain tumors in rats have been investigated using MRS ( 7-12). In some of these latter studies (7-10), crude spatial localization of tumor metabolites was
'
Presented in part at the Eighth Annual Meeting of the Society of Magnetic Resonance in Medicine, Amsterdam, The Netherlands, August 12- 18, 1989. Present address: University of Michigan, Department of Radiology, Ann Arbor, Mf 48 109-0553. 0740-3194/92 $3.00 Copyright 0 1992 by Academic Press,Inc. All rights of reproduction in any form rwrved.
96
'H MRS OF AN INTRACEREBRAL RAT GLIOMA
97
achieved by exploiting the limited sensitive volume of a small surface coil transmitter / receiver placed directly over the tumor; consequently, only tumors located superficially within the brain parenchyma could be investigated. Because most brain tumor models are those implanted in rodents (13-1 7), it is advantageous to employ a sensitive MRS method which can reproducibly localize spectra to small volumes (e.g.,
(1992)
Spatially Localized in Vivo 'H Magnetic Resonance Spectroscopy of an Intracerebral Rat Glioma' BRIAND. Ross,*HELLMUT MERKLE,KRISTY HENDRICH, R. SCOTT STAEWEN. AND MICHAELGARWOOD Department of Radiology, University of Minnesota, Minneapolis, Minnesota 55455 Received April 25, 1990; revised September 24, 1990 Surface coil MRI combined with spatially localized spectroscopy was used to noninvasively detect 'H signals from metabolites within an intracerebral malignant glioma in rats. The MRS pulse sequence was based upon two-dimensional ISIS, which restricted 'H signals to a column-shaped volume, combined with onedimensional spectroscopic imaging, which further resolved the signals into 8 or 16 slices along the major axis of the column. All experiments were executed with adiabatic pulses which induced uniform spin excitation despite the inhomogeneous radiofrequency field distribution produced by the surface coil transmitter. Surface coil MRI and MRS experiments were performed on phantom samples, normal rat brains, and rat brains harboring malignant gliomas. Spatially resolved in vivo 'H spectra of intracerebral gliomas revealed significantly decreased concentrations of Nacetyl-aspartate and creatine and increased lactic acid (or lipids) as compared to the contralateral hemisphere. These results demonstrate that metabolic abnormalities in intracerebral rat gliomas can be spatially resolved in a noninvasive manner using localized in vivo 'H MRS. 0 1992 Academic Press, Inc. INTRODUCTION
Magnetic resonance spectroscopy ( MRS ) provides a powerful means to noninvasively detect metabolites in living tissues. The application of MRS to the study of tumor metabolism is currently an active area of research due to its potential utility in diagnosis and in the evaluation of treatment protocols (e.g., see Ref. ( I , 2 ) ) .Recently, interest in 'H MRS of brain tumors has increased since preliminary measurements of brain tumors have revealed significant differences in metabolite levels between histologically different tumors (e.g., benign vs malignant gliomas), as well as between different subsets of the same tumors (3-5). It can be argued that metabolic abnormalities and efficacy of therapies can best be studied using animal models since it is possible to control many of the variables affecting tumor initiation and progression. Although subcutaneous tumors in rodents are the most common tumor models used for in vivo MRS studies ( 6 ) ,a limited number of intracerebral brain tumors in rats have been investigated using MRS ( 7-12). In some of these latter studies (7-10), crude spatial localization of tumor metabolites was
'
Presented in part at the Eighth Annual Meeting of the Society of Magnetic Resonance in Medicine, Amsterdam, The Netherlands, August 12- 18, 1989. Present address: University of Michigan, Department of Radiology, Ann Arbor, Mf 48 109-0553. 0740-3194/92 $3.00 Copyright 0 1992 by Academic Press,Inc. All rights of reproduction in any form rwrved.
96
'H MRS OF AN INTRACEREBRAL RAT GLIOMA
97
achieved by exploiting the limited sensitive volume of a small surface coil transmitter / receiver placed directly over the tumor; consequently, only tumors located superficially within the brain parenchyma could be investigated. Because most brain tumor models are those implanted in rodents (13-1 7), it is advantageous to employ a sensitive MRS method which can reproducibly localize spectra to small volumes (e.g.,
