Combined Fluorescence and White Light Laparoscopy

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If we wanted to build a fluorescence imaging system for minimally invasive surgery then there are a few things we would need to consider. We would want it to be simple to implement, reasonably lightweight and, most importantly, compatible with existing laparoscopes. We’d also like to be able to obtain a conventional white light view at the same time as the fluorescence. Researchers at GE have developed a device which meets all of these requirements, and recently published the details in the open access journal Biomedical Optics Express. Their suggested application is to help identify nerves during surgery, but the technique could easily be used for a range of purposes.

The new imaging device1 has two main components: an illumination source and a camera, both of which can be coupled onto a standard laparoscope. The illumination device is actually two light sources, a laser at 405 nm and a white LED. The LED is filtered to remove components below 450 nm, preventing interference with the laser wavelength. The output beams from both sources are combined using a dichroic filter and then coupled into a fibre light guide for delivery to the laparoscope.

The camera is a standard colour CCD camera with no particularly exciting features other than an external trigger line. The main change from normal operation is that a notch filter is placed in front of the camera to reject 405 nm laser light. So when the LED is turned off (and the laser is on) the camera only sees the fluorescence excited by the 405 nm laser. If the laser is turned off, and the white LED turned on, then the camera sees normal, white light, laparoscopic images.

To acquire near-simultaneous white light and fluorescence images the authors designed a control scheme to rapidly switch between LED and laser illumination. Alternate camera frames are acquired using the two imaging modes and custom software then separates the two channels and displays them side-by-side. The resolution of this combined imaging system is between 70 and 100 microns (depending on the imaging distance), which is similar to a normal laparoscope.

The device was tested using GE3082, a fluorescent contrast agent which increases its emission when it binds with myelin basic protein, a constituent of myelinated nerves. It was injected into the tails of a group of rats, which were then imaged four hours later during a simulated surgical procedure. The test was successful – the nerves are clearly highlighted in the fluorescence images, although in this case they are also easily identifiable under white light.

Although only one wavelength and one fluorescence stain were used for these experiments, the technique could be extended to work with multiple fluorescent agents. In fact a whole multi-spectral imaging system could be built if a further reduction in frame rate (or the purchase of a faster camera) could be tolerated. The technique isn’t revolutionary, but because it involves only a simple modification to existing laparoscope it should be relatively easy to translate into the clinic.

References

  1. Gray, D. et al., Dual-mode laparoscopic fluorescence image guided surgery using a single camera, Biomedical Optics Express, 2012, 3 p. 1880-90

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  1. Graeme Mutton says:

    FYI

    http://www.gastrojournal.org/article/PIIS001650851201308X/fulltext

    Nerve visualisation using Confocal laser endomicroscopy. Optiscan rigid endomicroscope would seem to fit with laporoscopic surgery.

    Worth exploring the link

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