Improved optical tissue compensation method for better cancer diagnosis

When it comes to cancer, clarity is key. The ability to visualize cancerous tumors and metastatic tissue in three dimensions (3D) can help clinicians diagnose the precise type and stage of cancer, while also informing the best methods of treatment. To obtain even clearer tissue for imaging, a Japanese-based research team tested the effectiveness of specialized hydrogels. Acting as a 3D molecular network, these hydrogels allow rapid elimination of fat from tissues, a factor of tissue opacification, without losing their structure. The material is used in several biomedical devices, including contact lenses.

They published their results online on June 21 in Macromolecular biosciences with the print edition published on September 16.

Since 1981, the leading cause of death in Japan has been cancer, ”said first author Chie Kojima, associate professor in the Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University. “We need new treatment methods and diagnostic techniques. 3D fluorescence imaging is one such approach that could prove indispensable for understanding multicellular systems at organ scale, as it can give us more information than traditional 2D imaging. This could be useful for personalized medicine in diagnosis, as well as to elucidate biological phenomena.

This type of imaging involves labeling certain molecular machines, such as proteins, to fluoresce with different colors depending on what they are. Light signals can be visualized in a variety of samples, from whole organisms down to the cellular level. However, most tissues are opaque, blocking the ability to see these signals. In 2D imaging, samples are sliced ​​thin, making the signals easy to see but removing the ability to view the entire system in 3D.

Previously, researchers used an approach known as CLARITY, in which tissues are embedded into polyacrylamide hydrogels. Fats are removed from the tissues and the refractive index of the medium is adjusted. The marked light signals can be viewed in 3D, but it takes a month for the cancerous tissue to clear up -; far too long for a patient waiting for a diagnosis, according to Kojima. During this time, the tumor would probably have spread.

The duration of the optical compensation process in the CLARITY method must be shortened for practical applications. “

Chie Kojima, first author

To reduce this time, the researchers used zwitterionic hydrogels, which are balanced in their charged molecules and maintain the structure of the tissue samples. Among several combinations of zwitterionic hydrogels, the team found that polymer hydrogels that mimic fat molecules on tissue appear to optically clear tumor tissue the fastest. According to Kojima, hydrogels are highly osmotic, which can help extract other fatty acids from tissue.

Blood vascular networks in murine brain tissue, as well as metastatic tumor tissue could be visualized in 3D using our system, ”said Kojima.

And they could visualize tumor tissue faster than in their previous attempts: what previously took a month could be achieved in a week with the enhanced approach.

Researchers continue to explore the technique and how to apply it to diagnose cancer in humans.

We are trying to apply our system for pathological diagnosis, ”Kojima said. “We expect it will be possible to diagnose an entire biopsy sample -; instead of thin slices -; which could prevent surveillance of small cancers.

Source:

Osaka Prefecture University

Journal reference:

Kojima, C., et al. (2021) Application of zwitterionic polymer hydrogels to optical tissue compensation for 3D fluorescence imaging. Macromolecular biosciences. doi.org/10.1002/mabi.202100170.

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