EFFECT OF MELANIN ON PHOSPHORUS T1S IN HUMAN-MELANOMA XENOGRAFTS STUDIED BY P-31 MRS

P-31 MRS resonance ratios of tumors depend on the T(1)s of the phospho rus compounds. The objective of the P-31 MRS study reported here was t o investigate whether the phosphorus T(1)s of melanomas are influenced by the presence of melanin. One amelanotic (COX-t) and one melanotic (ROX-t) human melanoma xenograft line were studied at two different tu mor volumes: 200 and 1000 mm(3). P-31 MRS was performed in nonanaesthe tized mice at 4.7 T. The T(1)s were measured by using the superfast in version recovery technique. Fraction of necrotic tissue in the tumors was determined by histological examination. The ROX-t tumors showed sh orter T(1)s than the COX-t tumors at a volume of 200 mm(3), where the fraction of necrotic tissue in the tumors was insignificant. The diffe rence was similar in magnitude for all resonances. The T(1)s were not significantly different for COX-t and ROX-t at a volume of 1000 mm(3), where the tumors of both lines had developed significant necrosis. Th e phosphorus T(1)s of melanomas without necrosis can be shortened sign ificantly by the presence of melanin. The magnitude of the T-1 shorten ing is similar for all major compounds. P-31 MRS resonance ratios of m elanomas are not altered significantly by correcting for effects of pa rtial saturation.