During an Intravascular Ultrasound (IVUS) intervention, a catheter with an ultrasound transducer is introduced in the body through a blood vessel and then pulled back to image a sequence of vessel cross-sections. Unfortunately, there is no 3D information about the position and orientation of these cross-section planes. To position the IVUS images in space, some researchers have proposed complex stereoscopic procedures relying on biplane angiography to get two X-ray image sequences of the IVUS transducer trajectory along the catheter. We have elaborated a much simpler algorithm to recover the transducer 3D trajectory with only a single view X-ray image sequence. The known pullback distance of the transducer during the IVUS intervention is used as an a priori to perform this task. Considering that biplane system are difficult to operate and rather expensive and uncommon in hospitals; this simple pose estimation algorithm could lead to an affordable and useful tool to better assess the 3D shape of vessels investigated with IVUS.