Overcoming the design challenges of image-guided surgery systems

Today’s operating rooms are vastly different from those of the past. Physicians are using live, high-resolution video of patients from intraoperative systems to enhance the precision of procedures like implant positioning, tumor removal, and angioplasty. The state-of-the-art sensors in image-guided surgery systems—essentially technological eyes—are allowing even highly complex surgeries to be minimally invasive for the patient.

The exceptional advantages of image-guided surgery systems warrant an examination of current system challenges and how they might be overcome with help from equipment based on GigE Vision®, an open standard for transporting video and control data over Ethernet networks.

Point-to-point connections
Behind the crisp, high-definition preoperative and intraoperative images used in image-guided surgery are millions of pixels of high-speed data, which must be transported, processed, displayed, and stored instantaneously with ultra-high reliability.

In today’s systems, most of the real-time functionality is achieved using point-to-point connections between a vision sensor in the modality and an image capture board in a PC. The images often need to be viewed on more than one display in the operating room, or by staff in a control room, observation room, or training area. This is accomplished by configuring additional point-to-point connections using PCs, graphic extension boards, display controllers, and other pieces of specialized hardware.

These point-to-point connections are very costly. They are also complex, difficult to manage, and expensive to scale. Moreover, as sensors continue to evolve to higher resolutions and faster frame rates, it is becoming increasingly difficult for these links to deliver the bandwidth needed for real-time image delivery.

Real-time image networking
One of the most significant improvements that can be made to drive down costs and improve clinical workflows is to deploy a networked video connectivity system that brings together all the image sensors, PCs, processing units, and displays into a common and seamless framework. Such a network would complement and interface with picture archiving and communication systems (PACS) based on the Digital Imaging and Communications in Medicine (DICOM) standard.

By having all the elements connected to a network and speaking the same language, multiple streams of video from different types of image sensors can be transmitted easily to any combination of PCs, processing units, and displays. This approach simplifies the implementation of advanced multi-stream applications, and substantially reduces the need for costly specialized equipment and custom cabling.The possibilities of a networked system are limitless.

For example, it is possible to combine images obtained during surgery with high-resolution 3D scans of a patient acquired before surgery. Or the sensor feeds from multiple modalities, such as intraoperative MRI and CT scans, can be fused to provide surgeons with in-depth, real-time views of a region of interest. Networked topologies also scale seamlessly to accommodate increasing bandwidth requirements and the addition of new modalities, processing nodes, and viewing stations, without sacrificing existing equipment.

In addition to networking, a modern medical video connectivity solution must also offer robust, reliable transport that can deliver imaging data in real time with virtually no delay between what the sensor sees and what is projected on displays. In image-guided surgery, where a patient’s life may be on the line, achieving minimum delay is of critical importance. And finally, to ensure interoperability and cost-effectiveness, the system must be based on mature, widely adopted standards.

Ethernet
Only one technology meets every one of these requirements: Ethernet—the world’s lowest cost, most ubiquitous transport platform. As a time-honored standard that is deployed in most of the world’s networks, including those for demanding real-time military and industrial applications, Ethernet is supported by a well-understood infrastructure based on mass-produced, low-cost chip sets, switches, and cabling.

Other connection standards meet some of the above requirements, but fall short in specific areas and do not offer networking capability. Camera Link®, for example, transports imaging data at high rates—up to 6.8 gigabits per second (Gb/s) over two copper cables—but streaming is done over point-to-point links of 10 meters or less, tethering cameras to PCs and image capture boards and restricting system design options.

Ethernet, on the other hand, offers exceptional networking flexibility, supporting almost every conceivable connectivity configuration, including point-to-point, point-to-multipoint, multipoint-to-multipoint, and multichannel aggregation. It also delivers high bandwidth. Gigabit Ethernet (GigE), the widely available third generation of the standard, delivers 1 Gb/s. The fourth generation, 10 GigE, now ramping into mainstream markets, delivers 10 Gb/s. Of additional note is that 10 Mb/s, 100 Mb/s, 1 Gb/s and 10 Gb/s can be mixed on the same switch and the equipment will automatically adapt, which ensures backward compatibility and permits system upgrades without sacrificing the equipment already in place. 

Ethernet offers long reach, allowing spans of up to 100 meters between network nodes over standard, low-cost Cat 5/6 copper cabling, and much greater distances with switches or fiber. And finally, Ethernet offers superior scalability, supporting meshed network configurations that easily accommodate different data rates and the addition of new processing nodes, displays, and switches.

GigE Vision
The benefits of Ethernet for high-performance imaging were first recognized in the industrial imaging sector about 10 years ago, when GigE was starting to be deployed widely in mainstream networks. The popularity of GigE for industrial vision applications led to the introduction by the Automated Imaging Association in 2006 of GigE Vision, a global open standard for distributing video and control data over Ethernet networks.

Figure 1 demonstrates how real-time imaging can be feasibly brought into today’s operating rooms.  

Figure 1: How real-time imaging can be brought into today’s operating rooms
(Click on image to enlarge)

A small-footprint, GigE Vision-compliant IP Engine in the C-arm converts x-ray images to IP packets for reliable, real-time transport over a standard GigE network. A GigE network switch multicasts the imaging data to a PC for control and storage; to a software-based video processing PC for error correction; and to a display in the control room. The processing PC sends the corrected image stream back through the network to the display in the control room for multi-window viewing, as well as to the three displays in the operating room – all in real time with low, consistent latency.

All three displays are equipped with vDisplay IP Engines, which are compact video receiver boards that convert the GigE Vision imaging stream to HDMI/DVI signals for viewing on high-definition monitors.

Today, dozens of leading hardware and software vendors offer GigE Vision compliant products, and the standard is used widely in real-time imaging and video systems for medical, military, traffic control, and manufacturing applications.

Version 1.2 of GigE Vision, ratified in January 2010, includes updates to meet growing demand for application architectures that make better use of Ethernet’s powerful networking capabilities. Past versions of the standard supported products like cameras, video converter devices, video driver software, and software development kits. Version 1.2 extends support to a rich variety of new video network elements. These include video receivers that display GigE Vision video and imaging data directly on standard displays, without the need for PCs or display controllers, as well as video servers, video processing units, management entities, and network-controlled devices.

GigE Vision allows all these network elements to interoperate seamlessly over the low-cost Ethernet platform, simplifying the design, deployment, and maintenance of imaging and video applications.

All GigE Vision compliant products must follow the connectivity framework laid out in the standard. However, many performance-related characteristics—such as reliability and latency—are subject to the quality of the implementation. To achieve the performance required for image-guided surgery systems, it is important to select products carefully.

Breaking ground
Manufacturers of x-ray equipment, MRIs, flat panel detectors, and other medical imaging systems have been embedding GigE Vision compliant video networking products into their systems for several years. These products, such as small-footprint video transmitters and receivers, stream imaging data from sensors and flat panel detectors to PCs in real time for processing and display. The implementations reduce system costs by replacing expensive image capture boards with performance-oriented, GigE Vision compliant driver software.

The software runs on the GigE network interface chips/cards (NICs) built into most PCs. Economies are also found in the affordable Cat 5/6 cabling or, where regulatory requirements call for electrical isolation, in cost-effective GigE fiber connections.The GigE Vision compliant equipment already in place in health care facilities represents an important first step in the rollout of advanced network solutions for image-guided surgery systems.

Video and imaging data from one modality can be multicast—sent simultaneously to multiple locations—through a switch, for example, to a processor for image correction, to a PC for storage, and to multiple video receivers for display, all in real time, with minimal amounts of specialized hardware. The long-distance reach of Ethernet allows each network element to be located where it makes sense, giving hospitals and other health care facilities more flexibility in system design than they have today.

As they evolve, real-time imaging and video networks will serve as important technology platforms for the medical community as it pushes forward into new frontiers of image-guided surgery. By leveraging the mainstream Ethernet networking platform and the GigE Vision standard, hospitals and health care facilities will be positioned to find new efficiencies in the way these advanced procedures are delivered, and broaden access for all.

About the author
John Phillips is a Senior Product Manager at Pleora Technologies, where his work focuses on delivering Pleora’s technical roadmap and on establishing a world-class application engineering and support program. Prior to joining Pleora, he spent 10 years with March Networks in software development, sales, and, most recently, product line management, where he guided development of advanced video solutions for the security market and played a key role in the company becoming a recognized market leader in that vertical segment. Before that, Mr. Phillips worked with Elcombe Systems and IBM. He holds a BSc in Computer Science from the University of Ottawa.