New way to enlarge tissues gives pathologists a closer look at cells

The cellular features used to diagnose certain diseases are often too small to be seen through a standard light microscope. While scanning electron microscopes (SEM) can magnify objects up to 10 million times -- revealing even subatomic particles in fine detail -- magnification power in the millions comes with a price tag in the millions, too, making diagnosis by SEM extremely costly.

"We can use expansion pathology to push conventional light microscopes beyond their current limits, which could have important applications in diagnostic pathology," said the study's co-lead author, Octavian Bucur, MD, PhD, of the Department of Pathology and Cancer Research Institute at BIDMC, who is also a Ludwig Cancer Center Research Investigator. "We're trying to replace the electron microscope -- an expensive technology that requires specialized training -- in the diagnosis of diseases."

"We can apply this method to any type of clinical sample and all types of human tissues, including normal and cancerous tissues," said co-lead author Yongxin Zhao, PhD, of MIT's Media Lab.

In 2015, MIT researchers -- led by the study's co-senior author Edward Boyden, PhD, an associate professor of biological engineering and brain and cognitive sciences at MIT -- developed a means of expanding cells and mouse brain tissue so that cells' internal features could be viewed under the conventional light microscope found in most labs. The team infused the biological materials with a polymer that swells up evenly when mixed with water, similar to the absorptive material inside baby diapers.

"If you can expand a tissue by one-hundred-fold in volume, all other things being equal, you're getting 100 times the information," said Boyden, who is also a member of MIT's Media Lab and McGovern Institute for Brain Research. "Now you can make diagnoses without needing an electron microscope. You can do it with a few chemicals and a light microscope."

In the current paper, Bucur, Zhao and colleagues -- including senior author Andrew Beck, MD, PhD, formerly of both BIDMC and Ludwig Cancer Research -- optimized the technique for human clinical specimens and diagnostic purposes. In addition to testing the technique on normal and cancerous breast, prostate, lung, colon, pancreas, kidney, liver and ovarian tissues, the team created a mathematical model based on morphological features of cells' nuclei to better discriminate between early, pre-cancerous lesions with high a probability of progressing to cancer and those with less probably of progressing to disease.

"ExPath improved the computational pathology diagnosis of these notoriously hard-to-differentiate lesions" said BIDMC researcher and study co-author Humayun Irshad, PhD.

"We showed that expansion can help us better computationally classify these early breast lesions," said Bucur. "Helping physicians discriminate between lesions at high-and low- risk for cancerous transformation could mean fewer unnecessary procedures for low-risk patients and earlier interventions for those at high risk."

In another experiment, the researchers demonstrated that ExPath could be used to reliably diagnose kidney minimal-change disease (MCD) without the use of an electron microscope. MCD is diagnosed based on the characteristic podocyte, elongations of the cell normally too tiny to be seen through a light microscope. But once the researchers expanded the sample tissues using the new technique, they could see the tell-tale sign of disease with the inexpensive, conventional microscope.