If you are procuring an image and video technology system for 3D integration in the operating room and beyond, there are several relevant questions that you should be asking before deciding on the best option. In this buyer’s guide to medical 3D integration, we try to explain how 3D image and video technology work and what you need to consider when evaluating needs, benefits and costs.
What you should be asking
How does 3D technology work?
What does 3D compatibility mean?
Why do I want to integrate 3D features?
What motivates recording in 3D?
What are the most important 3D features for my hospital?
Which 3D features can we actually integrate?
How do I know if my 3D source is truly vendor neutral?
What is required to make it suitable for medical professionals and to give the added benefit of extra image information?
How much are we prepared to pay for it all?
Medical 3D use is still evolving
Even though 3D has been seen in the consumer market for some time now, it is still evolving. So far, the main use for medical 3D video is within endoscopic surgery, such as laparoscopy. Doubtless, more medical applications will be developed, but keep in mind that there are significant differences with regards to requirements for medical 3D applications compared to consumer use – requirements that we hope to explain on a basic level in this guide.
What it takes to see in 3D
Interestingly, not all human beings are able to view the world in three dimensions. Around 5% of the human population cannot see in 3D. There are some online tests that do not require any additional equipment. For example, follow this link.
For humans to perceive 3D, two separate images must be registered, one by each eye. The two separate images are interpreted by the human brain. If both eyes saw both images, they would not be perceived as 3D (hence the reason you need to wear 3D glasses – the lenses work as filters, allowing each eye to see one image only).
If you happen to have some of those red/green glasses lying around, there is an even more accurate test to see if you actually have 3D vision here.
A word of warning: this type of tests is not meant to substitute a medical diagnosis made by a healthcare professional, such as your ophthalmologist.
To summarize: since not all humans are able to experience 3D vision, even with perfect viewing conditions, not everyone will be able to perceive 3D. The use of 3D for depth perception is however a very powerful tool for the clinician in the procedure.
Capturing 3D
To capture an image in 3D you need two image sensors (cameras) that are placed a certain known distance apart. That distance is used in post processing to render a 3D image. There are many articles debating the subject of precision in this field. For more information, please refer to your endoscopy vendor.
Connections and signal paths
For any 3D video source to be truly vendor neutral, the 3D video format needs to be transmitted using current standards. The following is a list of 3D compatible connections:
• SDI-3G
• SDI-6G
• SDI-12G
• DVI-D
• HDMI 1.4 or greater (HDMI 2.0 recommended)
• DisplayPort 1.1 or greater
Which format you actually need, depends on the resolution of the 3D video. To ensure the best value for money and to avoid getting caught out by technical constraints, avoid proprietary formats.
3D viewing station challenges
When using a 3D viewing station, the viewer needs to be aware of their head position for accurate 3D view and wear special 3D glasses.
The secret to 3D viewing is that the viewing station presents a different image to each eye. This can be achieved in several different ways, but it appears that each of these methods come with certain limitations – whether the position of the viewer, correct signal levels or cumbersome equipment.
The main method currently in use for display technology within the medical field is circularly polarized light. With this display technology, the viewer can tilt their head and still maintain the left/right separation needed to see the images in 3D format (although head movement means that stereoscopic image fusion will be lost due to the mismatch between the eye plane and the original camera plane).
Depending on the method being used, a display in 3D mode may give slightly different resolution and grey levels of the image compared to the original.
Integration of 3D features
When an integration provider tells you that their system is 3D compatible, that does not mean all features support 3D — and this is for good reason. Unfortunately, it is not enough to ask whether the integration system is 3D compliant, as this can have different interpretations and answers depending on who you ask.
Routing 3D images and video in the OR
Routing the live signal from the OR is the feature that is most commonly supported by integrated systems. This feature is relatively uncomplicated and generally does not entail many complications other than the fact that you must route the signal to a display that has 3D support.
Routing to a conference room
Next, if you are routing the signal to a nearby conference room, the same considerations apply as for routing within the OR, as long as the signal is carried by fibre. However, the signal path is more expensive in terms of cables and signal amplifiers. The conference room must have a 3D display, or the image is converted back to 2D by a converter before being routed to the conference room. Everyone who is looking at the monitor must be able to experience 3D vision and wear 3D glasses.
Recording 3D images and video
Another feature that is often requested is to be able to record 3D images and video. To do this, the capture card needs to support recording the full 3D signal.
Be aware that capturing a 3D signal will take up significantly more space in terms of size compared to 2D. To make sure that the file size does not become too large, an encoder with 3D support has to be incorporated in the recording and viewing station. The encoder will likely use the file format MVC (Multiview Video Coding) which is an amendment to the H.264 video compression standard. Still, the file size will be significant, meaning recording is potentially costly.
Even PACS administrators for systems that support the DICOM format used by 3D video are unlikely to accept the file size of a 3D video. The most common alternative is to store them on a local NAS server. Carefully consider your reasons for recording in 3D and who benefits from viewing the recorded material — is depth information an added benefit when replaying the procedure? To get depth information, you can only use a special 3D monitor, but without it, you can use any monitor in the hospital.
Broadcasting 3D images and video
When integrating 3D features broadcasting functionality is sometimes mentioned as a desirable feature. However, limiting bandwidth factors, the type of encoding used and the type and quality of monitor used by viewers makes this feature unlikely to be supported by any current integration system or provider known to Medical Imaging Technologies today. Remember that all viewers must be able to see in 3D, wear 3D glasses and use a monitor with 3D support — whether you are broadcasting over satellite or the internet.
Summary
To accomplish complete 3D integration, certain requirements need to be fulfilled. If recording and broadcasting features are included in your integration plans, there are even more factors to be considered.
The reality of 3D integration means that you have to fulfil the requirements of the entire chain: all the way from capture through routing to viewing. If not, you will not in fact achieve 3D.
In light of the costs and pitfalls involved in recording and replaying imaging material in 3D, it is legitimate to ask who benefits from what feature and in what way. The obvious gain in medical 3D technology integration lies in routing the live source within the operating room, when the surgeon is operating on a patient. To use 3D features beyond this, continues to be a trade-off with today’s technology.
Requirements for 3D
two different images are captured
compatible connections are used
viewer is able to experience 3D vision
viewer is wearing 3D glasses
the display has 3D support
ability to store large files
sufficient bandwidth
capture card capability
