Quantitative magnetization transfer studies of apoptotic cell death.

Magnetization transfer measurements were performed on samples of acute myeloid leukemia cells at early (36 h postcisplatin treatment) and late (48 h posttreatment) stages of apoptosis. Magnetization transfer ratio was calculated and a two-pool model was fitted to data at two powers and 16 offset frequencies of saturation pulse. No parameters changed significantly at early stages of apoptosis. At late stages, changes in magnetization transfer ratio were not significant, but quantitative model parameters showed a decrease in macromolecular proton fraction, M(0B), and an increase in the T(2) relaxation time of free water. Analysis also indicated an increase in the ratio R × M(0B)/R(1A), where R is the exchange rate between free water and macromolecular protons and R(1A) is the T(1) relaxation rate of free water. Changes in the magnetization transfer spectrum were largely attributable to differences in the free water pool and did not occur any earlier than changes in the average T(1) relaxation time, T(1obs).