2.1

Project description/methodology

In order to achieve the purpose of this project, suitable and reliable alternatives to fluoroscopy for visual acquisition and real time intravascular navigation guidance as well as contrast for luminography had to be identified.

For visual acquisition of the target vessels, ultrasound imaging was selected as a suitable, readily-accessible, radiation-free modality. Given the limitations of current technology and devices, medium to large-sized vessels (i.e. iliac and femoral arteries) were identified as appropriate targets. The vessel of interest is imaged using both two-dimensional (2-D) and three-dimensional (3-D) ultrasound imaging, which is then co-registered with anatomic landmarks to help formulate a detailed virtual vessel map that obviates the need for fluoroscopy and contrast ( Fig. 1 ).

Vessel map via coregistration of two-dimensional (2-D) and three-dimensional (3-D) ultrasound imaging.

To help acquire these images in motion-independent fashion, device-based sensors are applied to the patient emitting a low-powered electromagnetic field, enabling for vessel navigation in 3-D. The operator will be able to navigate within the vessel using real-time 3-D imaging that has been co-registered with previously obtained ultrasound images. This will allow for crossing of the lesion with a guidewire and subsequent use of intravascular imaging devices, angioplasty balloons, and stents to allow for a complete intervention. The accuracy of this system is within 1 mm and 1 degree , automatically adjusting for changes in heart rate, respiratory motion and patient movement ( Figs. 2 and 3 ).

Conceptual example of the “fusion screen” combining ultrasound rendering, IVUS and 3-D volume rendering without (left) and with (right) the guidewire.

The fusion map with coregistration with ultrasound background (A) and 3-D volume rendering (B).

For acquisition of key elements of the lesion’s characteristics such as location, length, severity of stenosis, histologic composition as well as post intervention verification of procedural success, the true vessel characterization (TVC) system provided both near infrared spectroscopy (NIRS) and intravascular ultrasound (IVUS) without the use of fluoroscopy or contrast. It has an IVUS axial resolution of 40–45 μm and a linear registration of IVUS to NIRS of − 0.7 ± 0.2 mm; all diameter and area measurements are accurate within a variance of 5% .

The proposed final sequence of events starts with ultrasound imaging of the leg using the LogiqE9 ultrasound with LEA Mapping and VNAV™ technology from General Electric (GE Healthcare, Wauwatosa, WI). It allows for coregistration, which creates a roadmap of the vessel and identifies the lesion of interest ( Fig. 1 ). MediGuide™ technology from St Jude Medical (St. Jude Medical, Inc., St. Paul, MN) allows for wiring of the vessel ( Figs. 2 and 3 ). It is followed by the use of the TVC Imaging System™ from Infraredx (Infraredx, Inc., Burlington, MA) to characterize the lesion dimensions and composition ( Fig. 4 A ). After completion of the diagnostic phase of the process, the interventional portion with deployment of an angioplasty balloon and/or stent is performed using the MediGuide™ technology ( Fig. 4 B). Post procedural assessment of success is then confirmed using the TVC Imaging System™ ( Fig. 4 C), the ultrasound platform ( Fig. 4 D) as well as the 3-D volume rendering ( Fig. 5 ). A complete diagnostic and interventional endovascular procedure without the use of fluoroscopy and contrast, making lead garments obsolete will be a reality.

The sequence of events (A) pre-procedure TVC Imaging, (B) angioplasty, (C) post procedure TVC imaging, and (D) post procedure Doppler imaging.

Pre (A) and post (B) procedure 3-D volume rendering.

2.2

Feasibility/Limitations

The ultrasound platform is already commercially available and has been used previously to construct a roadmap of the vessel of interest. It has also been demonstrated to have the diagnostic power to detect intraluminal navigation of guidewires and potential vessel dissection. The plan is to compare the diagnostic findings to those of conventional angiography in both normal and diseased subjects and assess the intermodality agreement.

The TVC Imaging System™ from Infraredx is already commercially available and has been validated in coronary procedures. It is also undergoing first-in-man uses for carotid and peripheral arteries . To be fully functional within the parameters of the proposed innovation it requires “MediGuide™ enabling” i.e. addition of the sensor on the catheter in order to enable detection and tracking by the MediGuide™ technology.

The MediGuide™ technology is already commercially available, and navigation in weak electromagnetic fields has been validated in electrophysiology procedures . At present a 0.014” guidewire but no guide catheters, angioplasty balloons or stents are “enabled”. In addition the MediGuide™ volume rendering software requires adaptation to become compatible with the input from the ultrasound and TVC Imaging systems. As previous work has been done with coregistration and integration of ultrasound and IVUS input into the MediGuide™ output, this step is expected to be achieved in a reasonably timely manner.

The potential limitations of this innovation are to be accounted for. NIRS has not been validated for lipid-rich plaque (LRP) detection in such large vessels. In particular, the diameter of the iliac arteries may be too large for successful NIRS detection of LRP imaging using the current catheter. However the work in first-in-man uses for carotid and peripheral arteries is a good start and should be built upon. The ability to detect vessel perforation, no-reflow, or distal embolization is an important challenge to the axial and temporal resolutions of both ultrasound technology and MediGuide™ volume rendering. Published reports describing early attempts at ultrasound-guided peripheral procedures lend credence to the capacity of this imaging modality to allow the operator to detect such occurrences. The initiation of the “proof of concept” stage should allow us to address further questions such as inter-operator reproducibility, impact of patient body habitus, procedural variables including duration and cost effectiveness.

2.3

Benefits/Anticipated outcomes

Previous efforts in the field of interventions have only achieved some reduction in contrast use and fluoroscopy time at the expense of ergonomics and procedure duration , likely deterrents to the adoption of these methods by the community at large. This project demonstrates the real potential of performing endovascular peripheral intervention without fluoroscopy or contrast in a practical, user-friendly way with the currently available technology.

The prospects in renal function preservation and radiation avoidance for both patients and operators are extremely attractive. For example, at our institution, more than a 1,000 peripheral angiograms are performed annually, including 400 interventions. The average yearly contrast use is around 49,000 cc. The fluoroscopy time amounts to more than 15,000 minutes. By achieving the proposed innovation and bringing it into daily practice, the goal is to work towards a completely contrast-less and fluoroscopy-less diagnostic and interventional approach for proximal lower extremity atherosclerotic peripheral artery disease (PAD). This would, in turn, obviate the need for radiation protection using lead garments, and therefore reduce the associated morbidity.

Another prospect of this novel procedure is a better understanding of the role of NIRS imaging for lesion measurements, stent length/diameter selection, and evaluating the stent results. This has not been properly explored to date, especially in peripheral procedures. The implications for future extended use of this technology are extremely attractive.

The prospect of extrapolating this concept to other procedures such as distal PAD, coronary and carotid interventions is another anticipated benefit of successful achievement of the current innovation. This is limited by the ultrasound technology’s capabilities, namely penetration and resolution (both temporal and axial). However as this project shows that there is room for novel use of existing technology.

We anticipate that the outlined approach offers an innovative and potentially practice-changing concept in the field of minimally-invasive catheter-based interventions, with an enormous projected impact on both patients and health care workers.