SPIN-LATTICE RELAXATION-TIME OF INORGANIC-PHOSPHATE IN HUMAN TUMOR XENOGRAFTS MEASURED IN-VIVO BY P-31-MAGNETIC RESONANCE SPECTROSCOPY - INFLUENCE OF OXYGEN-TENSION

Previous P-31-magnetic resonance spectroscopy (P-31-MRS) studies have suggested that the spin-lattice relaxation time (T-1) of the inorganic phosphate (P-i) resonance is shorter in well-oxygenated than in poorl y oxygenated tumors. Amelanotic human melanoma xenografts were therefo re subjected to P-31-MRS to investigate whether the T-1 of the P-i res onance might be a useful parameter for assessment of tumor oxygenation status. It was searched for possible correlations between the T-1 of the P-i resonance and oxygen tension or parameters closely related to oxygen tension, including P-31-MRS tumor energy status and blood suppl y per viable tumor cell. Oxygen tension, tumor energy status, and bloo d supply per viable tumor cell decreased with increasing tumor volume. In contrast to previous suggestions, the T-1 of the P-i resonance dec reased with increasing tumor volume and decreasing oxygen tension, tum or energy status, and blood supply per viable tumor cell, possibly bec ause the tumors developed necrotic regions concomitantly with the decr ease in oxygenation status, resulting in increased concentrations of f reely dissolved para-magnetic ions in the tissue. Consequently, the T- 1 of the P-i resonance can probably not be utilized to estimate the ox ygenation status of tumors, at least not in tumors with necrotic regio ns.