After surgically removing a tumor from a cancer patient, doctors like to send off some of the tissue for evaluation by a pathologist to get a better idea of whether the margins are cancer free and to guide further treatment decisions. But for technical reasons, completing the pathology report can take days, much to the frustration of patients and their families. Sometimes the results even require an additional surgical procedure.
Now, NIH-funded researchers have developed a groundbreaking new microscope to help perform the pathology in minutes, not days. How’s that possible? The device works like a scanner for tissues, using a thin sheet of light to capture a series of thin cross sections within a tumor specimen without having to section it with a knife, as is done with conventional pathology. The rapidly acquired 2D “optical sections” are processed by a computer that assembles them into a high-resolution 3D image for immediate analysis.
The microscope was developed in the engineering lab of Jonathan Liu at University of Washington, Seattle. Liu got the idea after receiving an email from Nicholas Reder, a medical resident in the university’s pathology department. Reder noted that when pathologists examine a tumor specimen under a conventional analog microscope, they must first prepare the sample. That involves the laborious process of taking a thick piece of tissue, slicing it into smaller pieces for embedding in wax before cutting them again into a few paper-thin sections suitable for mounting on traditional glass slides.
Reder thought there had to be a better way. He asked Liu if it was possible to build a scanner that offered “a sneak peek” at the surface of a fresh tissue sample. That would help doctors identify the tissue specimens containing tumor that would need a closer look with traditional, gold-standard pathology tests.
Liu’s team began brainstorming, taking into consideration cost, speed, spatial resolution, imaging depth, and sample size. Their choice was light-sheet microscopy. While the original concept of a light-sheet microscope was described nearly a hundred years ago, the availability of extremely fast and sensitive digital detector arrays in recent years has allowed light-sheet microscopes to become much more efficient for optical sectioning. Liu realized their ability to produce high-quality 3D images much more quickly than other microscopy methods could be a game changer for applications in clinical pathology.
There was a hitch: the primary users of light-sheet microscopes have been laboratory researchers who study small specimens and model organisms. The microscopes have evolved without clinicians and larger human tissue specimens in mind. Liu’s team set about to design a new version of a light-sheet microscope, inspired by Reder’s initial idea for a rapid tissue scanner.
As described recently in Nature Biomedical Engineering, their new microscope has an open-top design with all of the optical components positioned beneath a flat glass plate . This allows the surgical team to dip a tissue specimen of essentially any size and shape into a fluorescent staining solution and simply place it on the glass plate for rapid scanning. A camera attached to the microscope rapidly images the fluorescence generated from the scanning sheet of light and relays the digital data to a computer for 3D reconstruction.
The new microscope has many potential applications. The researchers have already shown the device produces high-resolution images of surgically removed prostate tissue, with its highly irregular, tough-to-image surfaces, in less than 10 minutes. The microscope visualizes the surface of breast tissue, which sits flatter on the glass, even faster. For example, a small area of breast tissue could be imaged in less than a minute, allowing pathologists to zoom in and out on a computer to examine the tumor margins and see important features, including areas of invasive cancer and benign growths.
The impressive speed suggests that the microscope might one day be used right in the operating room or in an adjacent pathology lab, helping surgeons to remove a breast tumor in its entirety while minimizing the removal of healthy tissue. That’s good news, given that many women undergoing lumpectomies today find themselves in the operating room a second or even third time when a conventional pathology report, obtained several days after the surgery is completed, reveals that some of their cancer might have been missed.
The researchers have also shown that the new microscope can be used to produce images of a biopsy specimen with the same level of detail as traditional pathology, with the added advantage of offering valuable structural information in three dimensions rather than two. Another bonus of the new microscope is that it allows doctors to image a tumor sample or biopsy without destroying it. As a result, the tissue can still be sent on for additional genetic or molecular tests, which are becoming increasingly essential as we make strides toward greater precision in cancer care.
The researchers say they’re now building an even better version of their new microscope, capable of capturing ever-smaller details that are of diagnostic importance and imaging specimens more deeply. The next step is to test the ability of this technology to perform in clinical studies.
In recent years, researchers have made major advances in understanding and treating cancer. But the tools used in diagnosing and staging cancer have changed little in the last 100 years. The hope is that this advance—and others to come—can usher the field of pathology into the digital age, alleviating frustration for patients and their families and, most importantly, translating to improved, potentially life-saving care.
 Light-sheet microscopy for slide-free non-destructive pathology of large clinical specimens. Glaser AK, et al. Nature Biomedical Engineering. [Epub ahead of print]
Jonathan Liu (University of Washington, Seattle)
NIH Support: National Cancer Institute