A team of researchers at Boston University have developed a novel ultrafast single-shot 3D imaging technique by the name of EventLFM that integrates an event camera into a Fourier LFM system to enable volumetric imaging at kHz speeds. The study was published in Light Science & Application.
a, Schematics of the setup. b, Recorded space-time event spike stream. c, Frames are generated from the raw event stream using the time surface algorithm. d, Each time-surface frame is reconstructed using a light-field refocusing algorithm. e, Depth color-coded 3D light field reconstruction of the object. f, An optional convolutional neural network refines the refocused volume, enhancing the 3D resolution and suppressing the noise artifacts. g, Time color-coded 3D motion trajectory reconstructed over a 45 ms time span. h, Illustrative experiment results on rapidly blinking neurons in a 75 µm thick brain section. Image Credit: Ruipeng Guo, Qianwan Yang, Andrew S. Chang, Guorong Hu, Joseph Greene, Christopher V. Gabel, Sixian You, and Lei Tian
Rapid volumetric imaging is essential for studying dynamic biological processes. Traditional scanning-based 3D imaging methods, such as light-sheet microscopy, confocal microscopy, and two-photon microscopy, offer high spatial resolution. However, these methods require beam scanning, which limits data acquisition speeds. Consequently, there is a trade-off between temporal resolution and the space-bandwidth product (SBP), which is defined as the 3D field-of-view (FOV) divided by the spatial resolution.
Fourier light field microscopy (LFM) consistently achieves high spatial resolution throughout the recovered volume by capturing light field information in the Fourier domain. However, conventional CMOS cameras' synchronous readout limitations create a bottleneck, restricting current single-shot 3D wide-field methods to less than 100 Hz at full-frame resolution.
This limitation hinders the recording of ultrafast dynamic biological processes that can exceed kilohertz speeds, such as blood flow dynamics, muscle tissue contraction, and voltage signals in mammalian brains, creating a significant technological gap.
In this study, the team demonstrated that EventLFM could reconstruct intricate dynamics of rapidly moving 3D objects with a temporal resolution of 1 kHz. The technique showed its capability to image high-frequency 3D blinking objects with pulse widths as short as 1 ms through controlled illumination experiments.
By imaging realistic neuronal activities in a mouse brain section simulated by a series of DMD patterns to create distinct spatiotemporal footprints at kilohertz rates, EventLFM successfully captured fast dynamic signals within scattering tissues. The team also demonstrated successful tracking and imaging of GFP-expressing neurons in C. elegans moving freely in a 3D environment, achieving a 500 Hz frame rate. Additionally, integrating EventLFM with a deep learning reconstruction network significantly enhanced 3D resolution and image quality.
Researchers now have a new tool to watch 3D dynamic biological processes at kilohertz speeds using this published study. The following is how these scientists sum up the workings of their system:
We designed EventLFM to integrate an event camera with a Fourier LFM system, enabling the imaging of complex, rapid biological processes at kilohertz rates with high 3D resolution.
They added, “It should be noted that the kilohertz frame rate demonstrated in our experimental results is determined by the accumulation time, which can be adjusted in the post-processing step without affecting the data capture speed. By reducing the accumulation time further, we can enhance the system's capability to capture dynamic processes beyond kilohertz rates.”
We highlight EventLFM's capability to image blinking neuronal signals in scattering mouse brain tissues and to track GFP-labeled neurons in freely moving C. elegans. Given its simplicity, ultrafast 3D imaging capability, and robustness in scattering environments, EventLFM has the potential to be a valuable tool in various biomedical applications for visualizing complex, dynamic 3D biological phenomena.
Journal Reference:
Guo, R., et al. (2024) EventLFM: event camera integrated Fourier light field microscopy for ultrafast 3D imaging. Light: Science & Applications. doi.org/10.1038/s41377-024-01502-5