Rabbit liver was loaded with ferrimagnetic particles of gamma -Fe-2 O-3 (designed for magnetic hyperthermia treatment of liver tumors) by injecting various doses of a suspension of the particles into the hepatic artery in vivo. Proton transverse relaxation rate (R-2) images of the livers in vivo, excised, and dissected were generated from a series of single spin-echo images. Mean R, values for samples of ferrimagnetic-particle-loaded liver dissected into approximate 1 cm cubes were found to linearly correlate with tissue iron concentration over the range from approximately 0.1 to at least 2.7 mg Fe/g dry tissue when measured at room temperature. Changing the temperature of ferrimagnetic-particle-loaded samples of liver from VC to 37degreesC had no observable effect on tissue R-2 values. However, a small but significant decrease in R-2 was found for control samples containing no ferrimagnetic material on raising the temperature from 1degreesC to 37degreesC. Both chemically measured iron concentrations and mean R-2 values for rabbit livers with implanted tumors tended to be higher than those measured for tumor-free liver. This study indicates that tissue R-2 measurement and imaging by nuclear magnetic resonance may have a useful role in magnetic hyperthermia therapy protocols for the treatment of liver cancer. (C) 2003 Elsevier Inc. All rights reserved.