Magnetic resonance imaging: a noninvasive tool for fetal and placental physiology.

Nuclear magnetic resonance imaging (MRI), a technique that utilizes biochemical information reflected in nuclear magnetic moments, can be used to image the uterus, fetus, and placenta of the human and nonhuman primate. MRI studies during pregnancy in the human and nonhuman primate provide soft-tissue structural information of considerable detail. MRI also offers the opportunity for noninvasive pharmacokinetic and toxicokinetic studies during pregnancy. Paramagnetic ions (Cu, Ni, Gd, Fe, Mn) after spin-lattice (T1) and spin-spin (T2) relaxation times in reproductive tissues. Changes in T1 and T2 alter the MRI image, reflecting uptake of paramagnetic ions by the uterus, placenta, or fetus. MRI provides a noninvasive method of monitoring body burden of selected xenobiotics during gestation. The use of paramagnetic labels on endogenous substances may also allow noninvasive determination of physiological parameters such as intervillous blood flow, placental metabolism, and placental transport during gestation.