Characteristic slow growing brain gliomas were induced in rats by a single subcutaneous injection of N-ethyl-N-nitrosourea (ENU) within 24 h of birth. A parallel control group of rats was injected with saline. Seven treated rats developed gliomas within 2 years. Periodic nuclear magnetic resonance imaging (MRI) of the brain in 3-mm slices at 1.5 Tesla and monthly plasma sampling for proton magnetic resonance spectroscopy (MRS) at 360 MHz were started 6 months after the injection of ENU. In the MRS experiments, the Fossel index, average of the line widths of the methylene and methyl peaks at 360 MHz, was determined from half-line widths of methyl and methylene peaks at 0.8 ppm and 1.3 ppm. In five of the ENU injected animals that developed histologically verified brain tumors, these were also observed by MRI without contrast agents. There was no consistent correlation between the imaged tumors and the Fossel index obtained through MRS during the course of the study where repeated observations were performed on individual animals, nor was there any consistent statistical difference in the Fossel index between ENU-treated and control animals. The results of this study demonstrate that slowly developing carcinogen-induced brain tumors in rats can be successfully and reliably monitored non-invasively by MRI but not by MRS of plasma.
Bibliographical noteFunding Information:
Correspondence to: Sigmund E. Lasker, Department of Medicine, New York Medical College, Valhalla, New York 10595, USA. Abbreviations: MRI, nuclear magnetic resonance imaging; MRS. nuclear magnetic resonance spectroscopy; VLDL, very-low density lipoprotein; LDL, low-density lipoprotein; HDL, high-density lipoprotein; FID, free induction decay. ‘Supported in part by a grant from the G. Harold and Leila Y. Mathers’ Charitable Foundation and by grant No. CA-46535 from the National Cancer Institute.
- brain tumors
- magnetic resonance spectroscopy
- nuclear magnetic resonance imaging