Researchers from the University of Arizona and Washington University, USA, have developed a dual mode imaging device that will help surgeons determine exactly where cancerous cells lie before excising a tumour. The new device is a cheaper, smaller, and more lightweight alternative to existing systems that typically require two camera types working in parallel.
In order to view a tumour, dies that fluoresce under NIR light are injected into the patient. This allows the entire tumour to be observed and indicates the precise location of the tumour. To ensure a clear image, the NIR camera requires a wide aperture to collect as much light as possible.
However, the surgeon also needs a visible light camera to see the tissue. These sensors need low apertures and high depth of field.
System developers must create systems that observe both NIR and visible light, which due to the differing requirements of both sensor types, typically means running two cameras next to each other. This leads to cumbersome equipment that is difficult to use.
‘Dual modality is the path forward because it has significant advantages over single modality,’ said author Rongguang Liang, associate professor of optical sciences at the University of Arizona.
The new system, developed by Liang and his colleagues, relies on a simple aperture filter that consists of a disk-shaped region in the middle and a ring-shaped area on the outside. The middle area lets in visible and near-infrared light but the outer ring only permits near-infrared light. When you place the filter in the imaging system, the aperture is wide enough to let in plenty of near-infrared light. But since visible light can't penetrate the outer ring, the visible-sensitive part of the filter has a small enough aperture that the depth of field is large.
Liang’s team is now adapting its filter design for use in lightweight goggle-like devices that a surgeon can wear while operating. They are also developing a similar hand-held instrument.
