Advances and Evolution of Medical Visualization Techniques – 3D endoscopy
Historically, surgical technology has been characterized as relatively conservative with low levels of innovation. With a number of ground-breaking developments, no longer is this the case. One particularly interesting area that has advanced recently is the field of 3D endoscopy, where visualization technology is transforming the tools available to surgeons and the effectiveness of their procedures. This, together with some of the other visualization technologies being developed, puts us on the brink of a technology revolution within the surgical device arena.
An overview of medical visualization technologies and endoscopy:
Over the past few decades, we have seen some significant advances in medical visualization technologies with the emergence and widespread use of sophisticated techniques such as magnetic resonant imaging (MRI) and X-ray computed tomography (CT scanning). These methods enable the surgeon to non-invasively visualize the internal structure of the human body in high resolution 3D, enabling a range of disease identification, screening and general medical applications.
In addition to these advanced visualization approaches, conventional optical visualization methods have also been advancing. One of the most interesting examples of this is surgical endoscopy. The benefits of minimally invasive surgery are well documented with less tissue injury and scarring, quicker recovery time and shorter hospitals stays, the end result is a more successful surgery. The classical 2D endoscope is a key tool in this process, enabling the surgeon to visualize the surgical site through an optical scope, rather than direct viewing through an open wound.
Rather surprisingly, the first use of optical endoscopes for internal visualization of the human body was reported almost 200 years ago, although it wasn’t until the development of miniature electric light bulbs in the early 20th century that endoscopes started to receive more widespread use. More recently, the development of digital imaging and display technologies have driven much of the development of modern endoscope instruments.
Many of these advancements have been driven by activities in the consumer electronics and gaming worlds and we see this trend continuing. Consumer applications have developed exponentially in response to the demand for increasingly sophisticated lighting, graphics, and visual effects all for a lower price point. As a result, the exotic semiconductor and imaging technologies just emerging from research labs 5-10 years ago are now widely available for use within the surgical arena. Some notable examples include:
- The development of the pill cam – a small fully encapsulated camera which passes through the digestive track,
- Chip-on-tip devices – where the optical image is encoded into an electrical video signal directly at the distal end of the endoscope inside the patient,
- LED surgical lighting using solid state illumination, and
- 3D endoscope products
The 3D Endoscope:
The original development of 3D video endoscopy can be traced back a couple of decades. This began with the emergence of high resolution, high quality video imaging chips enabling 3D visualization to be achieved by viewing the endoscope image not directly, but via two independent displays. These displays were viewed by the users’ left and right eye either through head up displays or other custom designed 3D viewers. At the time, several academic and industrial research groups demonstrated the principle of the technique without much commercial success. The increased cost of these displays, in addition to the dual channel imaging devices and optics, outweighed the benefit of the 3D visualization. Recently; however, 3D display technology has become widespread with the launch of 3D HD TV, the result being a range of new 3D endoscope products entering the market.
Today, 3D endoscopic visualization is seen as one of the key enabling technologies for surgical robotic systems, such as the DaVinci robot from Intuitive Surgical. In robotic surgery the surgeon is usually sitting at a workstation remote from the surgical site, manipulating the robotic tools through a computer controlled user-interface. While robotic surgery presents a number of advantages in terms of the precision of control of the surgical instruments and the ability to perform intricate surgery with minimal tissue damage, the electromechanical manipulation of the surgical tool means that the surgeon no longer has a direct physical sensory link between his hand and the surgical tool. This lack of direct sensory feedback is compensated to some extent by introducing 3D visualization using a specially modified endoscope. The restoration of 3D visualization in this example enables the surgeon to perform intricate surgical tasks which would prove difficult using a conventional 2D instrument.
How does a 3D endoscope work?
In reality, much in the same way as the human visual system. In the case of the endoscope, rather than using a single optical channel as in a classical 2D system, a pair of parallel optical channels are used to generate two images of the surgical site from two slightly different perspectives. These images can be relayed to an appropriate 3D display – either a pair of conventional 2D displays viewed separately by each of the surgeon’s eyes – or a single 3D display viewed by the user through a viewer or pair of 3D glasses. The optical technology used in most 2D and 3D endoscopes is based on a breakthrough developed by the British Physicist, Harold Hopkins, in the 1950’s. Hopkins invented the rod lens relay system that allows high quality optical images to be transferred from the main imaging lens at the tip of the endoscope, inside the body of the patient, back to an eyepiece at the proximal end of the endoscope so that it can be viewed comfortably by the surgeon. This imaging system superseded the coherent fiber bundle imaging systems that suffer from poor resolution. The breakthrough Hopkins made was in his use of a series of glass rod relay lenses to transfer the image from the distal to the proximal end of the scope. Using rod lenses, rather than conventional miniature lenses enabled the optical relay to be made from (easy-to-assemble) glass rods which are naturally easier to align and assemble, significantly simplifying manufacture and production. This solution proved so successful that it is still the basis of high quality optical scopes today. Manufacturing stereoscopic pairs of these systems is relatively straightforward and indeed stereo endoscopes for direct visualization have been on the market for a number of years and are used in microsurgical applications such as transanal endoscopic microsurgery. However, it has been the technological advances in digital imaging and high resolution display technologies, driven by the consumer electronics market, which has seen the recent upsurge in interest in 3D visualization.
Where to now?
Over the next few years it is likely that more enhanced visualization techniques will be developed in the fields of endoscopy, surgical microscopy, and general surgery. Some key areas with major potential include:
LED surgical lighting: There have been considerable advancements in general surgical lighting as a result of the introduction of solid state illumination and LEDs. The benefits of these new light sources extend beyond high efficiency lighting. Surgical lights developed from these sources can have a number of features built-in, which would simply not have been possible with conventional tungsten or xenon lighting. For example, the spectral characteristics of the light can be tuned by mixing different colors together enabling synthesized white light to be produced with specific wavelengths enhanced (i.e., blue or red light). This is just starting to be used successfully in surgical applications to highlight and enhance the contrast of specific tumor types. In the future, these digital light sources might also be used for fluorescent marker applications. This concept is actively being researched in fluorescence imaging for the detection of early stage bladder, cervical, and colon cancers.
Optical coherence tomography (OCT): OCT enables high resolution 3D imaging through tissue. With near infra-red wavelengths, tissue can be penetrated to several millimeters making the technique useful for visualizing a wide range of tissue structures including the retina, arteries, and skin. The ability to visualize sub-surface structures in high resolution helps make early detection of diseases possible (e.g., glaucoma). Soon, the potential to combine data from OCT with conventional visual images will open a range of possibilities allowing for more powerful diagnostic methods.
Fluorescence tagging and imaging: Fluorescent markers have been developed to accumulate or attach to diseased tissue. By exciting and detecting these markers, through the use of narrow band illumination and imaging techniques, high resolution and high sensitivity diagnostic techniques are being developed. The enhanced signal to noise that can be achieved with these methods can significantly improve the detection of cancers allowing for diagnosis at an earlier stage and better treatment success rates.
Smaller visualization systems: Driven by robotic and minimally invasive techniques, we expect to see interesting developments in visualization technologies aimed at inspecting and treating increasingly smaller structures. These will have applications for example in orthopedics, ENT, neurosurgery, and urology.
We believe 3D endoscopy, together with the above advancements in surgical technologies, is driving surgical technology into a new and exciting frontier. These developments enable not only enhanced direct visualization of the surgical site, but also provide better early stage diagnostic opportunities, resulting a larger range of tools at the surgeon’s disposal and, in turn, an overall improvement in diagnosing and treating a disease.
Dr. Euan Morrison  is the Senior Consultant at Sagentia Ltd.