In the presented case and protocol, we described the feasibility and efficacy of combining Fiber Optic RealShape, or FORS technology, and intravascular ultrasound, or IVUS, to reduce operator exposure during the endovascular treatment of peripheral artery disease or PAD. The past decades, there has been a major shift from open to endovascular treatment for PAD. During endovascular treatment, image guidance and navigation is conventionally provided by two-dimensional fluoroscopy, and digital subtraction angiography or DSA.
Fluoroscopy has some important limitations. The acquired images are reproduced in two dimensions instead of 3D, and in gray scales, and it requires long-term radiation exposure with the risk of health problems. Furthermore, to assess the result of an endovascular revascularization, for example, after plain old balloon angioplasty, one or two DSAs are made with nephrotoxic contrast to estimate the dynamic improvement of blood flow.
With this, eyeballing is needed to assess the increase of blood flow, and this technique also has the limitations regarding assessment of vessel lumen diameter, plaque morphology, and the presence of flow-limiting dissection after endovascular revascularization. To overcome these problems, new imaging technologies have been developed to improve device navigation, hemodynamics after treatment, and reduce radiation exposure, and use of contrast material. FORS combines image fusion with specially designed endovascular devices with embedded optical fibers that use laser light instead of fluoroscopy for a three-dimensional visualization of guidewires and catheters.
By sending laser light and analyzing changes in the returning light spectrum caused by twisting and bending of the optical fibers, the system can create a 3D reconstruction of the device over the full length of the embedded optical fibers. IVUS has the capacity for an optimal assessment of vessel dimensions. We stepwise present method of combining FORS and IVUS to show the potential of merging of both techniques in view of reduction of radiation exposure, improvement of navigation tasks, and treatment success during endovascular procedures for the treatment of peripheral artery disease.
In this case, we present a 65-year-old male with a history of hypertension, hypercholesterolemia, and coronary artery disease. In the past, the patient was treated for an abdominal aortic aneurysm and a right common iliac artery aneurysm by endovascular aneurysm repair in combination with the right-sided iliac branched device. Years later, acute ischemia of the lower extremity caused by occlusion of the left iliac EVAR limb was treated by embolectomy and the endo graft was extended in the external iliac artery on the left side to eliminate an aneurysm of the common iliac artery.
During follow-up, routine duplex ultrasound showed a significance stenosis in the left iliac limb, which was also confirmed by a CTA. To prevent recurrence of limb occlusion, a percutaneous transluminal angioplasty, or a PTA, was planned. You can see the CT scan and intercranial cardle order the transfers planes showing the corporate lesion and the stenosis over 50%in the left iliac limb.
The protocol and procedure is divided in several steps, first vessel segmentation. Secondly, volume registration followed by FORS shape registration. Thereafter, endovascular navigation to the aorta.
Then, pre-PTA IVUS diameter measurements, followed by the actual treatment, a PTA of the stenosis. Afterwards, IVUS diameter measurements after the PTA, and lastly, pressure measurements. For vessels segmentation, the CTA has to be uploaded into the FORS segmentation software to create a roadmap for navigation by segmenting the aorta and both iliac arteries.
This can be done by moving the cursor over the arterial structures. The arteries will point out in a blue highlighted color and can be selected by clicking on them. Ensure only the arterial structures of interest are selected in this step.
In this case, we select the abdominal aorta, and both common iliac arteries in combination with the left external iliac artery. Afterwards, segmented structures can be inspected visually by rotating the segmented vessels. Then volume registration has to be done.
In this case, we use a so-called 2D, 3D volume registration to align the preoperative and intraoperative position of the patient. To do so, two intraoperative fluoroscopy images need to be captured focusing on the field of interest which are the previous implanted endo graft and iliac limp, in this case. The C-arm needs to be positioned in two different positions, one with 45 left anterior oblique angle, and one with 45 right anterior oblique angle are captured and copied to the software.
The visible preexisting stent graft in the fluoroscopic images is used to align the segmented vessel volume into the real time imaging. First, the volume is translated towards the right location, overlaying the contours of the stent on the fluoroscopic images. Determine the correct windowing, so only the high house field values of the preoperative CTA are included to only visualize the stent graft.
Afterwards, the center of rotation is translated towards the center of the stent graft to enable rotation of the stent graft around its center. Now the stent graft is rotated to align the preoperative and intraoperative contours of the stent graft to complete volume registration. This is confirmed by adjusting the windowing to orientate body structures.
Now, FORS shape registration has to be done. The FORS devices are registered inside the operation theater to enable the usage without fluoroscopy. The FORS devices are positioned in the intervention area and subsequently two fluoroscopic images with a difference in angle of at least 30 degrees are acquired.
Select the captured angles in the FORS software and rotate a c-arm towards the required position. Copy the image by clicking on the symbol or icon presenting two documents. Now, the FORS technology automatically projects the guidewire in yellow, and the catheter in blue over the acquired thoracopic images and FORS technology can be used autonomously.
During the next step, the FORS technology is used for passing the lesion. The registered CTA segmentation is used as a roadmap during navigation. The black background indicates there is no fluoroscopic image captured so the only orientation is generated by the registered overlay.
You can see the iliac stenosis creates a resistant to the guidewire. Afterwards, the force guidewire is navigated past the stenotic lesion up to the abdominal aorta. Then the catheter is introduced past the stenotic lesion to remain access to the aorta.
No fluoroscopy is used during navigation. The force guidewire is exchanged for a 0.014 workhorse guide wire. As this workhorse guidewire is not supported by the FORS system, fluoroscopy is used to obtain the wires position.
Afterwards, the FORS enabled catheter is removed and exchanged for the IVUS catheter. The IVUS catheter is introduced towards the aortic bifurcation. Over here, you can see the IVUS images acquired during a pullback of the IVUS catheter from the aortic bifurcation towards the common iliac artery.
Lumen diameters and cross-sectional areas are measured at the level of the culprit lesion. Subsequently, the guidewire is exchanged for a standard guidewire to guide a PTA balloon. To treat a complete lesion, an eight millimeter PTA balloon is positioned at a stenotic lesion and fluoroscopy guided balloon inflation is performed.
Afterwards, the position is adjusted and the balloon is inflated for the second time. Each inflation is performed for two minutes. The inflation process is visible by contrast enhancement of the balloon.
The intraluminal diameters after PTA are quantified by pulling back the IVUS catheter from the aortic bifurcation towards the common iliac artery. To validate the increase of lumen diameter, post PTA pressure measurements can be performed. After quantification, the IVUS catheter is switched to the FORS catheter again, and the FORS catheter is positioned proximal to the treated stenotic lesion.
Pressure can be measured, and the catheter can be pulled back distally to the stenotic lesion, and again, blood pressure can be measured. Instead of making a 2D digital subtraction angiogram or DSA using contrast, the effect of PTA in this case is quantified by using IVUS. Lumen diameter, increased from 4.8 millimeter pre PTA to 7.0 millimeter post PTA.
And cross-sectional luminaria area increased from approximately 28 square millimeter pre PTA to 44 square meter post BTA. No significant drop in blood pressure cranial according to the stenotic lesion after treatment suggests that PTA successful. During this procedure, total fluoroscopy time was one minute and 53 seconds with a total air Kerma of approximately 28 mGy, and a dose area product of approximately eight grade per square centimeter.
Over here, the differences in radiation exposure on the different steps of the protocol are placed side by side to enhance the differences. The vessel segmentation performed in the presented therapy to create a roadmap, does not require extra radiation and this step is not present within the conventional therapy. The volume registration and force shape registration does both require two single exposure shots, which are extra, as these steps are not presented in conventional therapy.
The intervascular navigation phase does not require any radiation with FORS, as the segmented vessel structures are used as a road map for navigation. This phase normally requires continuous fluoroscopy exposure, and the radiation exposure will increase rapidly in case navigation or recanalization is hard to succeed. Furthermore, the exchange of guidewires requires fluoroscopy as only the FORS guidewire can be visualized without radiation.
The quantification of the stenotic lesion in the presented therapy is performed with IVUS which doesn't require any radiation or nephrotoxic contrast material. In contrast to conventional DSA requires both radiation and nephrotoxic contrast. And finally, the pressure measurements with the FORS catheter don't require any radiation but with the conventional catheter fluoroscopy is required.
In this case, we describe successful treatment of a stenotic lesion in peripheral artery disease in which the combination of image fusion, FORS, and IVUS technology led to a minimal radiation exposure and no contrast medium use. In an era of increasing number of endovascular procedures and the correlated increased cumulative radiation exposure for both patients and treatment teams, the culmination of these technologies shows a safe turn towards the possibility of minimizing or even eliminating radiation exposure and contrast usage during these procedures. In addition, the use of IVUS to quantify stenotic lesions and the direct treatment effect provides a more objective outcome measure compared to the surgeon's assessment of contrast flow during a DSA.
Future research must include more patients with more complex lesions to demonstrate the effect on radiation exposure and confess use and to show whether merging of both techniques in one device has potential.
