A magnetic resonance imaging based method for measurement of tissue iron concentration in liver arterially embolized with ferrimagnetic particles designed for magnetic hyperthermia treatment of tumors

Rabbit liver was loaded with ferrimagnetic particles of γ -Fe2 O3 (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 (R2) images of the livers in vivo, excised, and dissected were generated from a series of single spin-echo images. Mean R2 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 1°C to 37°C had no observable effect on tissue R2 values. However, a small but significant decrease in R2 was found for control samples containing no ferrimagnetic material on raising the temperature from 1°C to 37°C. Both chemically measured iron concentrations and mean R2 values for rabbit livers with implanted tumors tended to be higher than those measured for tumor-free liver. This study indicates that tissue R2 measurement and imaging by nuclear magnetic resonance may have a useful role in magnetic hyperthermia therapy protocols for the treatment of liver cancer.