Currently there is no reliable way to determine, during tumor-removal surgery, whether the excised tissue is completely cancer-free at its margins — the proof that doctors need to be confident that they removed all of the tumor. It can take several days for pathologists using conventional methods to process and analyze the tissue.
A new microscope can rapidly and non-destructively image the margins of large, fresh tissue specimens with the same level of detail as traditional pathology, in no more than 30 minutes. The new lightsheet microscope offers other advantages over existing processes and microscope technologies. It conserves valuable tissue for genetic testing and diagnosis, quickly and accurately images the irregular surfaces of large clinical specimens, and allows pathologists to zoom in and “see” biopsy samples in three dimensions.
Current pathology techniques involve processing and staining tissue samples, embedding them in wax blocks, slicing them thinly, mounting them on slides, staining them, and then viewing these two-dimensional tissue sections with traditional microscopes — a process that can take days to yield results.
Another technique to provide realtime information during surgeries involves freezing and slicing the tissue for quick viewing. But the quality of those images is inconsistent, and certain fatty tissues — such as those from the breast — do not freeze well enough to reliably use the technique.
By contrast, the open-top light-sheet microscope uses a sheet of light to optically “slice” through and image a tissue sample without destroying any of it. All the tissue is conserved for potential downstream molecular testing, which can yield additional valuable information about the nature of the cancer, and lead to more effective treatment decisions.
Slide-based pathology is still an analog technique, much like radiology was several decades ago when X-rays were obtained on film. The new system images tissues in 3D without having to mount thin tissue sections on glass slides. The intact tissues are digitally imaged, so the need to prepare slides is bypassed. Valuable tissue can be used for purposes that are becoming ever more important for treating patients, such as sequencing the tumor cells and finding genetic abnormalities that can be targeted with specific drugs and other precision medicine techniques.
The light-sheet microscope also offers advantages over other nondestructive optical sectioning microscopes that process images slowly and have difficulty maintaining the optimal focus when dealing with clinical specimens, which always have microscopic surface irregularities.
The new microscope can both image large tissue surfaces at high resolution, and stitch together thousands of two-dimensional images per second to quickly create a 3D image of a surgical or biopsy specimen. That additional data could one day allow pathologists to more accurately and consistently diagnose and grade tumors.
The researchers configured various optical technologies in new ways, and optimized them for clinical use. The open-top arrangement, which places all the optics underneath a glass plate, allows imaging of larger tissues than other microscopes. The team is currently working on speeding up the optical-clearing process that allows light to penetrate biopsy samples more easily. Future areas of research include optimizing the 3D immunostaining processes, as well as working with machine learning experts to develop algorithms that can process the vast amounts of 3D pathology data the system generates, with the ultimate goal of helping pathologists zero in on suspicious areas of tissue.