Wide-field computational imaging of pathology slides using lens-free on-chip microscopy

Lens-free holographic microscopy provides wide-field images with 3D focus adjustment of pathology slides for high-throughput and cost-effective human disease diagnostics. Widescreen Pathology Imaging whole human tissues with a conventional light microscope can be cumbersome, requiring the user to stitch together 500+ individual small images to get a full view of the entire tissue. This microscopy and digitization process is largely confined to advanced laboratories in developing countries. Greenbaum et al. have developed a lens-free microscope based on low-cost holographic technology, which allows imaging of large fields of view—about 100 times greater than high-resolution conventional microscopes. The lens-free imaging uses a small chip, allows for 3D focusing through thick tissue samples, and can colorize the resulting images. With this device, the authors successfully imaged invasive human cancer cells, abnormal cells in Pap smears, and “sickled” cells in whole-blood smears, with spatial resolution and contrast sufficient for clinical diagnosis. In one demonstration, a pathologist was able to distinguish cancerous from benign human tissue using images from the lens-free microscope; the assessment matched conventional light microscopy in 74 of 75 images. With its wide field of view, high resolution, and speedy readout, this lens-free platform could benefit pathology laboratories in both developed and developing countries. Optical examination of microscale features in pathology slides is one of the gold standards to diagnose disease. However, the use of conventional light microscopes is partially limited owing to their relatively high cost, bulkiness of lens-based optics, small field of view (FOV), and requirements for lateral scanning and three-dimensional (3D) focus adjustment. We illustrate the performance of a computational lens-free, holographic on-chip microscope that uses the transport-of-intensity equation, multi-height iterative phase retrieval, and rotational field transformations to perform wide-FOV imaging of pathology samples with comparable image quality to a traditional transmission lens-based microscope. The holographically reconstructed image can be digitally focused at any depth within the object FOV (after image capture) without the need for mechanical focus adjustment and is also digitally corrected for artifacts arising from uncontrolled tilting and height variations between the sample and sensor planes. Using this lens-free on-chip microscope, we successfully imaged invasive carcinoma cells within human breast sections, Papanicolaou smears revealing a high-grade squamous intraepithelial lesion, and sickle cell anemia blood smears over a FOV of 20.5 mm2. The resulting wide-field lens-free images had sufficient image resolution and contrast for clinical evaluation, as demonstrated by a pathologist’s blinded diagnosis of breast cancer tissue samples, achieving an overall accuracy of ~99%. By providing high-resolution images of large-area pathology samples with 3D digital focus adjustment, lens-free on-chip microscopy can be useful in resource-limited and point-of-care settings.