Abstract. This paper introduces a new patient-mounted CT and MRI guided interventional radiology robot for percutaneous needle interventions. The 5 DOF robot uses ultrasonic motors and pneumatics to position the needle and then insert it progressively. The needle position and inclination can be registered in the images using two strategically placed fiducials visible in both imaging modalities. A first prototype is presented and described in terms of its sterilization, CT and MRI compatibility, and precision. Tests showed that 1) it is entirely sterilizable with hydrogen peroxide gas, 2) no image artifacts or deformations are noticeable in the CT and MRI images, 3) does not affect the SNR of MR images, and 4) its mechanical error is less than 5mm.

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