Thrombolytic therapy with rtPA increases the risk of hemorrhagic transformation (HT) after cerebral ischemia. We employed contrast enhancement MRI with Gd-DTPA to detect HT in a rat model of embolic stroke treated with rtPA and a glycoprotein IIb/IIIa receptor antagonist, 7E3 F(ab')2, at 4 h after embolic stroke. Male Wistar rats were subjected to embolic stroke and treated with the combination of rtPA and 7E3 F(ab')2 (n=12) or with saline (n=10) at 4 h after onset of stroke. MRI studies were performed immediately and at 24 h after embolization using a 7-T system. Histological measurements were obtained at 48 h. With Gd-DTPA, T1WI images and permeability related MRI parameters (the blood-to-brain transfer constant, Ki, and the distribution volume of mobile protons, Vp) of 15 out of 18 animals showed hyperintensity regions in gross or microscopic HT areas at 24 h, confirmed histologically at 48 h post stroke. Contrast enhancement MRI detected six of seven (86%) animals with gross HT and nine of eleven (82%) animals with microscopic HT at 24 h after ischemia. Two of eighteen animals with HT, had MRI indices of hemorrhage at 3 h post stroke. However, compared to HT data measured histologically at 48 h in embolic stroke rats, the enhanced areas by Gd-DTPA at 24 h were larger, and the patterns (time, intensity and region) did not directly correlate to the subtypes of HT, i.e., gross or microscopic hemorrhage. Contrast enhancement MRI using Gd-DTPA provides a method to detect gross and microscopic HT after stroke in rats.