Photoacoustic tomography

A method of rapid visualization of tumor tissue

Sergey Syrov, XX2 century

Breast cancer is the most common type of cancer in women. Every year in the world they get sick 1 250 000 – 1 300 000 a man is dying 400 000 – 500 000 . If cancer is diagnosed at an early stage and the tumor is small, it is possible to perform a lumpectomy – an organ-preserving operation in which the breast is not completely removed, but only the affected tissues are cut out.

However, currently there is no reliable way to monitor whether all cancerous tissues have been successfully removed right during the operation. The best methods of analysis take a considerable time – several days, too long for the surgeon conducting the operation to take their results into account. As a result, about a quarter of women who have undergone lumpectomy surgery go to the operating table for the second time, because part of the tumor remained in place.

Researchers from the Washington University School of Medicine in St. Louis and the California Institute of Technology (California Institute of Technology) report the beginning of the development of a technology for scanning and imaging a tumor sample suitable for checking in real time whether the tumor has been completely removed. An article about the development was published on May 17 in the journal Science Advances.

Now the new technology, called photoacoustic tomography, is faster than standard analysis methods, but still not fast enough to use it during surgery.

"This is a proof of concept that we can use a photoacoustic way to visualize breast tissue and get images that look similar to those that we get using traditional staining methods, but without any tissue processing," says Deborah Novack, co-author of the invention.

The work is not finished, the scientific team is working on improving the technology to reduce the time required to scan the sample to 10 minutes. Then the method can be used during operations. The modern generally accepted method of tissue analysis was developed in the middle of the XX century. It is based on staining tissue samples, which helps to recognize diseased and healthy cells.

There are other methods. When removing large tumors, doctors use intraoperative histological express examination - after the tumor is extracted, it is frozen, the sample is fixed in a gel–like substance (polyethylene glycol and polyvinyl ethanol). The tumor sample becomes strong and can be cut. The resulting sections are transferred to glass and stained for pathohistological analysis. The preparatory procedure takes about 10 minutes. In most cases, 5-7 minutes is enough to analyze the drug. Thus, during surgery, the surgeon can get a preliminary conclusion about the histological structure of the removed sample within 12-16 minutes.

But this method does not work well with adipose tissue, and there is a lot of it in the mammary gland, so the surgeon finishes the lumpectomy without knowing for sure how successful the operation was.

"Right now we don't have a good method for evaluating the success of breast cancer operations," says study co–author, Professor of Surgery Rebecca Aft.

Currently, a tumor removed from the breast is examined under a microscope, and the results get to the surgeon only after a few days.

How does the new method work? The development uses a phenomenon known as the photoacoustic effect. When a short pulse of light hits the material, the latter heats up and expands slightly, which produces sound waves that can be detected and used to build an image.

"All molecules absorb light at a certain wavelength," says another co–author of the work, Professor Lihong Wang. – This is what makes photoacoustic visualization such a powerful method. In fact, you can see any molecule if you have the ability to produce light of the desired wavelength. None of the other imaging technologies is capable of this, neither ultrasound nor X-ray. Light is the only tool that allows you to get complete biochemical information."

The researchers tested the technology's performance by scanning sections of tumors obtained from three patients. For control, the samples were also studied by traditional methods.

An image obtained by photoacoustic method is similar to a colored sample in all key parameters. The architecture of the tissue and subcellular details, such as the size of the nuclei, are clearly visible.

The image on the left was obtained by the traditional method of coloring,
on the right – using photoacoustic tomography.

Thus, if the technology comes into practice, doctors will not need to change the approach to analyzing the images obtained. It remains to achieve a reduction in scanning time.

"We expect that the process will be accelerated," says Wang. "In this study, we had only one channel for emitting light. If you have multiple channels, you can scan in parallel, this will reduce the visualization time. Another way to speed it up is to shoot the laser faster. Each laser pulse gives one data point. Faster ripple means faster data collection."

"One day we will be able to take a tissue sample directly from a patient, put it in a machine in the operating room and understand in minutes whether we have removed the entire tumor or not," Aft concludes.

Portal "Eternal youth" http://vechnayamolodost.ru  22.05.2017