To improve the tool (guide wire and catheter) guidance in interventional radiology, a new approach is to project 3D X-ray Angiography (3DXA) information in real time onto a fluoroscopy image ("\emph{3D Augmented Fluoroscopy"} - 3D AF). Recovering the acquisition geometry is a crucial step for such augmented reality application. As 3DXA and fluoroscopy images are acquired on the same vascular C-arm, a machine-based 3D-2D registration is possible. The feasibility of such an approach was proved and demonstrated in \cite{gorges05}. As a result, a complete Augmented Reality (AR) system, which enables to superimpose the 3DXA onto real time fluoroscopy images is going to be developed and installed in one of the vascular room of our institution. The system promises to help the radiologist to guide the tool to the pathology to be treated without the need to inject contrast medium. The X-ray dose, injected volume of contrast agent, procedure time and patient discomfort are expected to be reduced. This paper extends our previous work \cite{gorges05} in two ways. First, the study to assess the precision of the machine-based registration is completed, including various C-arm orientations and different focal lengths. A mean 2D error of 1 mm was observed. Secondly, a preliminary clinical evaluation of the AR system is reported and clinical evaluation grid is proposed as a ground to an objective and perceptual evaluation of such an AR application implying many observers and patient cases. This study demonstrates the potential of the 3D AF to improve navigation in interventional radiology.