Even with a TASC type C/D lesion, acceptable results of EVT have been reported in patients with aortoiliac disease (Yamauchi et al. 2019; Leville et al. 2006). Even for a very long total occlusion, once the guidewire is passed, a good result can be obtained by stent or stent graft implantation; the passage of the guidewire is very important. Additionally, because a fatal outcome due to vascular perforation or injury is possible in patients with aortoiliac lesions, the guidewire should be passed through the most optimal route possible. Various methods for passing the guidewire to a CTO lesion have been reported, including IVUS guidance, echo-Doppler (duplex) guidance, intravenous ultrasound guidance, bidirectional wiring, and subintimal angioplasty (Kawasaki et al. 2008; Schmidt et al. 2012; Kawarada et al. 2010; Hishikari et al. 2015). However, no gold standard method has been established because each method has its weaknesses.
The CTf3D-RM method does not require a special technique or device to perform the CTO intervention. This method involves highly objective guidewire manipulation that is secured by advancing the guidewire according to the virtual occluded vessel displayed on the angiographic image. The CTf3D-RM can follow changes in the flat panel inch size, panning, tube angle, and magnification. Thus, there is no need to create a new roadmap each time, and the procedure can be continued using the previously created roadmap. This method may contribute to shortening the procedure time, decreasing the number of guidewires needed, and reducing the amount of contrast medium used. Although the lesion in the present case was very complex, the time required to pass the guidewire was as short as 9 min, and the procedure could be completed without using an extra guidewire. In addition, the whole image of the vessel can be obtained, which is very helpful when choosing the puncture site of the femoral artery or when placing a stent.
Several reports have described the feasibility of image fusion of preoperative multidetector CT, cone-beam CT, or magnetic resonance angiography with intraprocedural fluoroscopy for creation of a roadmap during EVT and neurointervention (Jones et al. 2018; Sailer et al. 2015; Ierardi et al. 2016; Schwein et al. 2017). These reports suggested that it is easy to obtain the whole image of the vessel of interest, which can contribute to safety by reducing contrast agent use and radiation exposure (Schwein et al. 2017). Certainly, contrast-induced nephropathy is problematic for patients with chronic kidney disease, and although several effective methods have been reported, it seems that the CTf3D-RM technique can serve as another such method (Fujihara et al. 2015; Hayakawa et al. 2019; Mariani Jr et al. 2014). A major limitation of this fusion roadmap technique seems to be patient movement and image artifact. Other problems include different patient positions during preoperative CT or magnetic resonance angiography and interventional procedures. According to one study, a mismatch of several millimeters may not be clinically significant in aortoiliac lesions (Ierardi et al. 2016). Additionally, in previous reports, roadmaps were characterized by drawing opened vessels. These reports were mainly intended to create roadmaps for opened vessels to place wires and devices without using contrast agents. However, the most important point of our method is to visualize the details of the occluded vessel, mainly using the creation of a 3D roadmap as a support tool in precise wiring for the CTO lesion. Therefore, our method emphasizes the construction of a virtual vessel based on an accurate tracing of the central line of the occluded vessel and accurate reconstruction of the posture during the preoperative CT imaging. The difference between our method and those described in previous reports is that our method is not mainly intended to treat opened vessels, but rather to assist the passage of guidewires within the CTO by accurately depicting the occluded vessel and creating virtual occluded vessel. In the present case, as confirmed by IVUS after crossing through the guidewire, all of the guidewire passed through the intraplaque route. Although the posture and vessel course may change and the roadmap may shift because of the prolonged procedure time, it is relatively easy to readjust the roadmap using bone and artery calcification. The iliac artery is located within the pelvis and is relatively unaffected by changes in position; however, it is convenient to use a fixation device for long-term position fixation. The procedure can be performed without using the fixation device; in such cases, however, it may be necessary to correct the deviation between the fusion image and the angiography image more frequently. We believe that accuracy of the CTf3D-RM technique depends on postural fixation of the patient during the procedure and constant correction of image shifts using the location of vessel calcifications and bones. Even if this method is used, the image may shift, in which case it is desirable to refer to another modality such as IVUS.