BACKGROUND: An effective method to enhance the accuracy and sensitivity of magnetic resonance imaging (MRI) is to select a targeted contrast agent. OBJECTIVE: To prepare gadopentetic acid -polybutylcyanoacrylate nanoparticle (Gd-PBCA-NP) and to investigate its liver-targeted values in animal experiments.DESIGN, TIME AND SETTING: A comparative observation was performed at the Laboratory of Department of RadiologicelCenter, Nanfang Hospital between September 2004 and January 2005. MATERIALS: Gd-PBCA-NPs were prepared by anionic emulsion polymerization. METHODS: A total of 18 Wistar rats were randomly divided into 3 groups, with 6 rats per group: Gd-DTPA, PBCA-NP, and Gd-PBCA-NP. Following caudal venepuncture (catheter remained), rats received 0.1 mmol/kg Gd-DTPA, 10 mL/kg PBCA-NP, or 10 mL/kg Gd-PBCA-NP. MRI scans (coronal and transverse) were performed prior to and after different enhancement protocols using a head coil for transmission and reception of the signal. Immediately after contrast medium injection, dynamic data of each group were acquired at 5, 15, 30, 60, and 120 minutes using imaging parameters the same as for the pre-contrast images. MAIN OUTCOME MEASURES: The morphology of Gd-PBCA-NPs was observed using transmission electron microscope. The size and the index of size distribution were measured through the use of laser granulometer (Malvern-3000HS). The Gd ion concentration in the dialysate was determined by inductively coupled plasma atomic emission spectroscopy for calculation ofencapsulation efficiency and loading capacity of Gd-PBCA-NP. The enhanced rate of the liver at each time point was calculated. RESULTS: The morphology of Gd-PBCA-NPs was spherical shape with core-shell structure and without adherence between particles. The average size of Gd-PBCA-NPs was 65.7 nm, and the index of size distribution was 0.09 measured by dynamic light scattering. The average encapsulation efficiency and loading capacity of Gd-PBCA-NPs were 81.97% and 51.23%, respectively. After intravenous injection of Gd-DTPA, the enhanced rate of the liver was 35.2% and 48.6% at 5 and 15 minutes respectively and the kidney was obviously enhanced; at 30 minutes, the enhancement of the liver recovered to normal level. After intravenous injection of Gd-PBCA-NPs, the average enhanced rate of the liver was 3.4%, 22.7%, 36.1%, 56.4%, and 24.8% at 5, 15, 30, 60, and 120 minutes accordingly. After intravenous injection of PBCA-NP, the enhancement of the liver was not found. CONCLUSION: Gd-PBCA-NPs can be taken as liver-targeted MRI contrast agents and have potential application value in MRI.