The distribution of relaxation rates of water in "normal" (autopsy) samples of canine and human brain shows considerable overlap with that for brain tumor samples. The following ranges of values for the spin-spin relaxation rates were observed: for normal brain gray matter, 8.6 to 11.3 sec-1 (mean, 9.5 sec-1); for normal brain white matter, 13.3 to 15.7 sec-1 (mean, 15.5 sec-1); for six types of malignant tumor, 4.8 to 13.4 sec-1 (mean, 9.3 sec-1); for five types of benign tumor, 7.1 to 16.4 sec-1 (mean, 11.5 sec -1). Spin-lattice relaxation rates showed a similar pattern. At least two nonexchanging water components with different relaxation rates were indicated by the analysis of the spin-spin relaxation measurements for the white matter samples.
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