We developed a robot system that can be used for image-guided experimental procedures on small animals, where the goal is to perform physical actions at specific positions identified on a preoperative image The animal is first placed in a fixture that is compatible with all imaging systems of interest, including PET, SPECT, CT, MRI After imaging, the fixture is attached, registered to the robot system, where the image-guided intervention is performed This system has been applied to perform pO(2) measurements with physical probes based on tumor hypoxia images obtained in an animal PET scanner This paper focuses on the design, validation of the robot system The validation is performed using a phantom, includes a new method for estimating the Fiducial Localization Error (FLE) that is based on the measured Fiducial Distance Error (FDE) The results indicate that the robot system can position the measurement probe at a defined target with a mean error that is less than 0 4 mm