LIFE SCIENCES


researchers being able to buy fully formed instruments for cellular imaging. Te image sensors that go into these super


resolution microscopes have undergone their own gradual advance, the biggest change being the shiſt from CCD to CMOS. Tis is the case throughout life science imaging, not just for super resolution microscopy. ‘Te newer microscopes of Leica, Nikon or Zeiss will only use scientific CMOS,’ commented Dr Gerhard Holst, head of science and research at camera maker PCO. Sensitivity is particularly important when


imaging live cells, as the signals returning from fluorescent molecules can be extremely faint. Te disadvantage with early super resolution techniques like STED and PALM is that they use an intense laser to excite fluorescent molecules in the cell to get the signal, which


I think in the future, in


my opinion – and it might change – there will be only CMOS


kills the cells. A lot of the new super resolution techniques, however, like lattice light-sheet microscopy, can image live tissue over time without bleaching the cells. ‘While it’s important to see the cells clearly,


there’s a definite trade-off in terms of cell longevity and being able to track processes inside cells over time. Tat’s where sensitivity becomes important, because the more sensitive the camera, the less laser illumination power is needed,’ explained Rachit Mohindra, product manager at Photometrics, which supplies cameras for life sciences. Sensitivity is one critical characteristic for image sensors used in life science imaging,


but also low noise and speed, according to Holst. ‘Many of the new microscopy methods that improve resolution or give detailed information about living organisms, they need speed,’ he said. ‘Tey need to record a number of images to reconstruct the image the researcher is interested in.’


Rise of CMOS Life science imaging has traditionally been based on CCD image sensors because the image quality used to be better than the CMOS alternative. Now, however, CMOS, and particularly scientific CMOS (sCMOS), has


STUDYING CORAL REEFS


reached a point where its performance equals or betters CCDs in the majority of cases. ‘A lot of [life science] investigations still


use CCD cameras, but mainly for historical reasons,’ observed Holst. In January 2015, PCO were informed that Sony had decided to stop making CCDs. ‘Tat was another major push towards CMOS,’ Holst commented. He added: ‘I think in the future, in my opinion – and it might change – there will be only CMOS.’ Electron multiplying CCDs (EMCCDs)


are one option for imaging in low light applications. ‘EMCCDs are very sensitive, but complex and not easy to control – there have


Photometrics’ Prime-BSI camera has a backside- illuminated sCMOS sensor


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The Bay of Biscay’s cold water coral habitats have become important biodiversity hotspots and home to many species. Research has recently been published by the French Research Institute for Exploitation of the Sea (IFREMER) to investigate the health of these ecosystems, and assess the damage being done by human activity. The IFREMER team used adapted vision systems to survey 24 of the Bay’s canyons plus three locations between adjacent canyons. The images enabled them to identify 11 coral habitats, formed of 62 coral species, at depths between 50 and 1,000 metres. Two methods to capture images were used: from a


towed stills camera moving at 0.9m/s, and from a remotely operated vehicle (ROV) running a Sony FCB-H11 colour block camera, which delivers up to full HD images. ‘Light deteriorates quickly


underwater, and while cameras such as the FCB-H11 can capture down to 1lx, there is little significant light found below 200m, and no sunlight beyond the twilight zone (200m to 1,000m),’ said Sony Image Sensing Solutions’ Marco Boldrini.


‘Lighting also needs to be carefully controlled, however, as at depth the presence of particles such as silt cause an effect similar to high-beam headlights in heavy rain,’ he continued. The research team highlighted that several


images were discarded because of sediment clouds obscuring them.


According to Boldrini, this


makes it very difficult to automate lighting control, and even in a more controlled system such as the ROV, an operator would ideally have the ability to calibrate lighting and exposure times to maximise images. ‘Water also has a


particularly interesting effect on light,’ said Boldrini. ‘With a refractive index of 1.333, it shrinks the field of view by 25 per cent, and any camera chosen needs to take this into consideration.’ The Sony FCB-H11 colour block camera has a 50 degree horizontal viewing angle, making it suitable for this application.


December 2017/January 2018 • Imaging and Machine Vision Europe 19


Photometrics


Rusya007/Shutterstock.com


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