Quantitative phase imaging (QPI) is an effective and label-free method for cell and tissue imaging in biomedicine, enabling nanoscale three-dimensional reconstructions of biological samples in a non-invasive manner. Meanwhile, quantitative biophysical parameters such as refractive index, dry mass, matter density, and skewness can be extracted from the quantitative phase shift, providing both morphological and quantitative biophysical information for digital pathology. Recent research combining quantitative phase imaging with deep learning has been exploited towards virtual staining and dynamic blood cell examination, which was reported as a high throughput approach to detecting the SARS-CoV-2 virus. Nevertheless, current QPI methods are mostly based on bulky and complex microscope platforms with limited penetration depth, which means invasive sampling or sectioning of diseased tissues is usually required for pathological diagnosis. Such invasive approaches limit the in vivo application of QPI in clinical diagnosis, which can be crucial for early diagnosis of cancer.
In a new paper published in Light Science & Application, a team of scientists from TU Dresden, Tsinghua University, and Max Planck Institute for the Science of Light realized quantitative phase imaging (QPI) with an ultra-thin lensless fiber endoscope.
They developed a new algorithm named far-field amplitude-only speckle transfer (FAST) method to reconstruct the incident light field from the far-field speckles detected on the other side of the fiber endoscope. Digital refocusing can be realized from single-shot measurements without any mechanical movement, which significantly increases the depth of field of the microendoscope to several millimeters and gives more degrees of freedom in sample examinations. Unlike conventional fiber endoscopic imaging modalities, this new endoscopic imaging technology enables three-dimensional quantitative phase imaging with nanoscale axial sensitivity and lateral resolution in the micron range via direct recovery of the incident complex light field. These scientists summarize the performance of their lensless ultra-thin endoscope:
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“Almost all the current endoscopic imaging techniques rely on intensity imaging modalities. Due to the phase distortion in the optical fibers, quantitative phase imaging through a fiber endoscope is still challenging. We developed a new computational approach to decode the incident light field from far-field speckles. This advanced technology enables digital refocusing and three-dimensional reconstruction of cancer cells.”
“The miniature lensless microendoscope is so far the tiniest quantitative phase imaging probe with micron-scale lateral and nanoscale axial resolution, paving the road for in vivo label-free characterization of cells and tissue with minimal invasiveness” they added.
“Both morphological and quantitative biophysical information can be measured from our computational lensless fiber microendoscope, which is also a cost-effective laser system. This paves the road for wide clinical applications of the fiber endoscope, especially in the early diagnosis of cancer and tumors.” the scientists forecast.