The Future of Imaging for Endovascular and Open Surgery

Background

Vascular surgery has pioneered the development of various novel, minimally invasive catheter-based endovascular procedures within the confines of the open surgical operating room (OR). Portable image intensifier-based C-arm systems were the original imaging platforms on which catheter-based therapies have evolved in the hands of vascular surgeons. Thus far, the portable C-arm imaging system has been the signature imaging tool in the OR that heralded the entry of open vascular surgeons into the endovascular interventional space. With the advent and rapid evolution of imaging technologies in the OR, vascular surgeons are now required to have an increased understanding of both basic and advanced imaging techniques.

As the reach and complexity of endovascular therapies have evolved with advancements in endovascular devices such as steerable catheters, novel conformable stents, and stent grafts with custom-made branches or fenestrations, imaging technologies have also evolved in parallel. Image intensifiers in the portable C-arm imaging systems have been replaced with flat panel-based digital image detector systems and provide better image quality, signal-to-noise ratio, and dynamic range with little to no geometric distortions. However, the portable nature of these C-arm systems is still a limitation for having a more powerful X-ray tube with better cooling capabilities. Because of the advanced imaging demands for longer and more complex vascular procedures, fixed angiography imaging suites, traditionally the province of interventional cardiologists and interventional radiologists, have become commonplace within the OR environment. Often referred to as hybrid rooms, they allow for both “open” surgical procedures and catheter-based endovascular interventions to be optimally performed in the same operating suite. Although expensive, hybrid ORs, for the very first time, have paved the way for intraoperative cone-beam CT imaging and preoperative 3D image fusion guidance in the hybrid OR. This has been followed by technologies such as flexible endovascular robotics and the integration of multiple imaging modalities including transesophageal echocardiographic imaging (TEE), intravascular ultrasound (IVUS), intracardiac echocardiography (ICE), preoperative computed tomography (CT), and magnetic resonance imaging (MRI) within the hybrid OR.

Indeed, the rapid evolution of imaging and endovascular devices is symbiotic and synergistic. Despite the evolution of intraoperative advanced imaging capabilities, there has been an increasing concern about the long-term effects of occupational radiation exposure to the surgical team and ergonomics of radiation protection gear. Consequently, newer methods are evolving for real-time monitoring of radiation exposure and minimizing the amount of radiation employed during these procedures.

The goal of this chapter is to impart a broad overview of the recent evolution of advanced X-ray and multimodal imaging techniques for vascular surgery interventions and to provide a glimpse into potential future imaging and catheter navigation technologies that could improve the safety and efficacy of endovascular procedures while minimizing the amount of radiation exposure to the patient and healthcare team in the hybrid OR.

X-Ray Imaging and Hybrid Operating Rooms

Although alternate radiation-free imaging modalities such as ultrasound and MRI are available and less invasive, diagnostic imaging for endovascular interventional and surgical procedures has primarily been superseded by multi-slice conventional CT imaging, invasive 2D X-ray fluoroscopy and angiography. Despite being a 2D projection imaging technique, the primary advantage of 2D X-ray angiography is considered better with spatial resolution of around 0.2 mm in imaging smaller vessels with temporal resolution of ∼20 ms after injecting a bolus of an iodinated contrast agent into the vessel of interest.

Portable C-Arm Imaging Systems

Although the portable image intensifier–based C-arm imaging system has been the staple imaging modality for vascular surgery for many years, it has continued to evolve with technological advancements. For example, the image intensifier-based X-ray detector system has been replaced by the flat panel-based digital detectors; these have better sensitivity and lower noise levels, potentially offering better distortion-free image quality at a lower radiation dose. In addition, newer X-ray tubes in mobile C-arms with higher power generators – in the order of 25 kW – and better cooling capabilities enable higher penetration power even in obese patients. Moreover, these allow uninterrupted imaging for longer endovascular procedures than was possible with fixed C-arm angiographic imaging systems. ^, Radiation exposure to both patients and the surgery team needs to be carefully considered during the usage of mobile C-arm imaging systems in the OR. ^, Perhaps the most revolutionary development is 3D imaging in upcoming mobile C-arm imaging systems. Although there has been some preliminary work using this 3D imaging technique during bronchoscopic and orthopedic procedures, ^{, ,} routine clinical use of this technology for vascular imaging is still evolving.

Recent advancements in mobile C-arm imaging systems, including image fusion and overlay capabilities, are very relevant. In most vascular surgery practices, the portable low-end mobile C-arm imaging system continues to be the primary imaging modality or a backup imaging option to the fixed hybrid OR. Moreover, portable C-arm imaging–based interventional suites have been increasingly used to set up office-based vascular practices ( Fig. 33.1 ). With the technological gap between portable and fixed C-arm imaging systems narrowing, mobile C-arms could represent a very practical and economical option for an outpatient interventional or endovascular suite, permitting both the technical and professional revenues to be captured in an office-based vascular surgery practice.