In vivo measurements of NMR relaxation times

Abstract

A series of solenoidal NMR probes were built to measure T₁ and T₂ relaxation times in vivo in the mouse, over the frequency range of 5 to 60 MHz, using inversionrecovery and spin‐echo pulse sequences. KHT tumors growing in the legs of C₃H mice were studied and compared with normal mouse legs. The tumor relaxation times were studied at 10 MHz during the course of tumor growth and as a function of frequency when the course of tumor growth and as a function of frequency when the tumor had a mass of approximately 0.9 g. Mouse legs with tumors have higher T₁ and T₂ values than those without tumors over the frequency range of 5 to 60 MHz. Significant changes in both relaxation times were detected before a palpable mass could be detected. T₁ contrast between normal and tumor‐bearing legs decreased with increasing frequency, while T₂ contrast remained nearly constant. A comparison between in vivo and in vitro measurements was done using four different types of sample preparation: live mouse, dead mouse, excised whole mouse leg, and tissue sample. These studies showed small but significant differences between the relaxation times measured in vivo and those measured in vitro.