31P-nuclear magnetic resonance spectroscopy in vivo of four human melanoma xenograft lines: spin-lattice relaxation times

Abstract

Phosphorus spin-lattice relaxation times ( T 1s) were measured in vivo by 31P-nuclear magnetic resonance spectroscopy in tumors from four amelanotic human melanoma xenograft lines grown subcutaneously in BALB/c- nu/ nu mice. The T 1s were analyzed in relation to tumor volume, fractional tumor water content, and fraction of necrotic tumor tissue. The following resonances were studied: phosphomonoesters (PME), inorganic phosphate (P i), phosphodiesters (PDE), phosphocreatine (PCr), and nucleoside triphosphates γ, α, and β (NTPγ, α, and β). Two different techniques were used to measure the T 1s: superfast inversion recovery (SUFIR) and conventional inversion recovery (IR). The SUFIR and IR methods gave similar results. Tumors in the volume range 100–3000 mm 3 were studied. The PME, P i, PDE, and PCr resonances showed significantly longer T 1s than the NTPγ, α, and β resonances at small tumor volumes. The T 1s at small tumor volumes also differed significantly between the tumor lines. The T 1s either decreased or remained unchanged with increasing tumor volume; the volume-dependence of the T 1s differed significantly between the tumor lines but not between the resonances. Calculations based on the T 1s measured here indicated that the errors in PCr/P i and NTPβ/P i resonance ratios due to partial saturation can vary with tumor volume but are usually <20% at a repetition time of 2.0 s and <15% at a repetition time of 3.0 s. There was no correlation between the T 1s and fractional tumor water content. On the other hand, the T,s showed significant correlations to fraction of necrotic tumor tissue across the tumor lines; the T 1s of all resonances with the exception of the PDE resonance decreased with increasing fraction of necrotic tumor tissue.