[en] Objective: To investigate the value of macrophage activity imaging (MAI) in the diagnosis of brain and spinal cord lesions in rat model of multiple sclerosis (MS). Methods: Twenty LEW rats were divided into 15 model rats and 5 control rats. MS animal model, experimental autoimmune encephalomyelitis (EAE) was induced by the injection of peptide 35-55 of myelin oligodendrocyte glycoprotein (MOG_35-55), MRI was performed on the third day of the acute stage of disease. The brain and spinal cord of' rats were scanned by 3.0 T MR scanner (Siemens Trio Tim) with quadrature wrist joint coil. The T₂W and T₁W images, Gadolinium enhanced T₁W images in 3D volume were obtained respectively. The MAI were obtained at 24 hours after intravenous injection of ultra small superparamagnetic iron oxide (USPIO) as contrast medium on T₂WI. The workstation with special software was used for the reconstruction images of brain and spinal cord of rat in multiple orientations. Results: Fifteen MOG35₅5-EAE rats model of' MS were successfully induced. The great majority lesions of central nervous system in acute stage were located in the brain (58/63) and less in the spinal cord (5/63). The main manifestation of EAE lesions presented was hyperintensity on T₂WI and hypointensity on T₁WI, and some lesions had enhancement after Gd-DTPA injection. The EAE lesions presented as hypointensity on MAI images, but some of them were found to be isointensity on T₂WI. The enhancement pattern was discrepant between USPIO and Gd-DTPA. The sensitivity of depicting lesions of MOG_35-55-EAE rat at acute stage were higher on T₂WI (14/15) and MAI (13/15), and the detection rate was 100% (15/15) if they were combined. Gd-DTPA enhanced T₁WI had a lower sensitivity (7/15). All the MAI findings were negative in the control rats. Conclusions: MAI can complement the drawback of conventional MRI techniques by continuously monitoring the inflammatory activity of EAE lesions, and it could raise the detection rate of EAE lesions by combining with T₂WI. Gd-DTPA enhanced T₁WI monitors the breakdown of the blood brain barrier. MAI and Gd-DTPA enhanced MR imaging are complementary in the diagnosis and monitoring of EAE lesions. (authors)