Early identification of sites of embryo implantation in rats by means of gadolinium-enhanced MR imaging

To determine if magnetic resonance (MR) imaging techniques can be used to examine sites of embryo implantation in intact rats, pregnant animals were imaged with gadopentetate dimeglumine-enhanced MR imaging approximately 10 hours after initiation of implantation on day 5 of pregnancy. T1-weighted, three-dimensional SPGR (spoiled gradient-recalled acquisition in the steady state) sequences were used to image the volume of abdomen containing the uterine horns before and after injection of gadopentetate dimeglumine into a femoral venous catheter. While unenhanced images provided little detail in uterine tissue, analysis of the gadolinium-enhanced abdominal images with interactive vascular imaging allowed easy identification of sites of embryo implantation along both uterine horns in four of four pregnant rats. These punctate patterns of enhancement match those of macroscopic bluing after injection of Evans blue dye. Similar gadolinium-enhanced MR imaging of nonpregnant rats produced only a slight, generalized enhancement of entire uterine horns. The authors conclude that local increases in extracellular fluid volume, vascular permeability, and blood flow in the uterus may all contribute to the gadolinium enhancement of the implantation sites. They propose that this approach can be used in experimental settings to provide information regarding embryo implantation unaccessible with traditional approaches. In clinical settings, gadolinium-enhanced MR imaging may be used to examine potential causes of infertility, including luteal phase defects.