Abstract
Here we demonstrate widefield (field diameter = 200 μm) fluorescence microscopy and video imaging inside the rodent brain at a depth of 2 mm using a simple surgical glass needle (cannula) of diameter 0.22 mm as the primary optical element. The cannula guides excitation light into the brain and the fluorescence signal out of the brain. Concomitant image-processing algorithms are utilized to convert the spatially scrambled images into fluorescent images and video. The small size of the cannula enables minimally invasive imaging, while the long length (>2 mm) allow for deep-brain imaging with no additional complexity in the optical system. Since no scanning is involved, widefield fluorescence video at the native frame rate of the camera can be achieved.
Highlights
Imaging deep inside biological tissue such as the brain is vital for many applications
Resolution below ~3 μm is challenging due to cross-talk between adjacent cores[5,6]. Another approach for microendoscopy uses a miniaturized microscope with gradient index (GRIN) microlenses[9,10,11]
The GRIN microlenses need to be used in conjunction with a regular microscope[9,10], or a miniaturized microscope[11], both of which significantly increase the complexity of the system
Summary
Imaging deep inside biological tissue such as the brain is vital for many applications. Various other designs have been proposed or demonstrated as summarized in several review articles[15,16] None of these approaches provide the combination of deep penetration, small size and low cost for widespread use in fluorescence imaging of the deep brain. Due to its small size and large effective imaging area, the cannula is able to achieve the comparable field of view as that obtained via much larger GRIN-lens probes but with significantly less tissue damage. We demonstrated this technique, which we call computational-cannula microscopy (CCM) for high-resolution, wide-field fluorescence microscopy of samples in air[17,18]. It takes less than 0.2 s to compute each frame on a desktop computer (Dell XPS 8700, Intel Core i7-4790 3.6 GHz, 32GB RAM)
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