Abstract
Conventional two-photon microscopes use photomultiplier tubes, which enable high sensitivity but can detect relatively few photons per second, forcing longer pixel integration times and limiting maximum imaging rates. We introduce novel detection electronics using silicon photomultipliers that greatly extend dynamic range, enabling more than an order of magnitude increased photon detection rate as compared to state-of-the-art photomultiplier tubes. We demonstrate that this capability can dramatically improve both imaging rates and signal-to-noise ratio (SNR) in two-photon microscopy using human surgical specimens. Finally, to enable wider use of more advanced detection technology, we have formed the OpenSiPM project, which aims to provide open source detector designs for high-speed two-photon and confocal microscopy.
Highlights
Conventional two-photon microscopes use photomultiplier tubes, which enable high sensitivity but can detect relatively few photons per second, forcing longer pixel integration times and limiting maximum imaging rates
The maximum shot noise limited signal-to-noise ratio (SNR) of Photomultiplier tubes (PMTs) is fundamentally restricted because a finite photon detection rate imposes a maximum number of photons per pixel that cannot be exceeded without pushing the detector into saturation or damaging it
The actual SNR will be lower because the electron multiplication process in a PMT results in additional electronic shot noise, called excess noise, which reduces the shot-noise limited SNR below the level predicted from the photon shot noise alone[4]
Summary
Conventional two-photon microscopes use photomultiplier tubes, which enable high sensitivity but can detect relatively few photons per second, forcing longer pixel integration times and limiting maximum imaging rates. We introduce novel detection electronics using silicon photomultipliers that greatly extend dynamic range, enabling more than an order of magnitude increased photon detection rate as compared to state-of-the-art photomultiplier tubes We demonstrate that this capability can dramatically improve both imaging rates and signal-to-noise ratio (SNR) in two-photon microscopy using human surgical specimens. Photon counting is insensitive to variations in electron multiplication and so eliminates excess noise[5], but the need to sequentially detect photons further reduces dynamic range, resulting in even lower maximum imaging speed for a given SNR. Current detector technologies force a tradeoff between resolution and resilience against scattering on one hand, and imaging throughput and SNR on the other
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