What are some uses of sound waves

Hear what it looks like in the body - New method uses sound waves to generate medical images

The photoacoustic process is non-invasive and does not generate any radiation exposure. A glimpse into an operating room of the future: the patient on the operating table is still under anesthesia. A tumor has just been removed from his lungs. The operation went well - the tumor was completely removed. But before the chief doctor declares the operation over, she scans the operated area with a hand scanner. An image of a lymph node appears on the computer screen in front of her. She looks for metastases of the tumor. These migrate preferentially into the surrounding lymph nodes. Controlling the lymph nodes that are near the removed tumor is therefore particularly important to improve the patient's chances of recovery. If they are infected with cancer cells, they would have to be removed. The surgeon is relieved that there are no signs of metastases in the patient's lymph nodes. The team can end the operation.

Sound carries information from inside the body

What is currently fiction could soon become a reality. It is not yet possible to visualize metastases so easily in routine operation. But in the foreseeable future, such a technology could be available to medical professionals. It bears the somewhat bulky name “multispectral optoacoustic tomography”. The procedure was developed in Germany by two experts in medical imaging: Professor Dr. Vasilis Ntziachristos and Professor Dr. Daniel Razansky from the Helmholtz Center Munich. The two researchers made use of a very old principle of medical diagnosis, as Razansky explains: “The doctor places two fingers on the stomach or back, knocks and listens attentively to the noises that are made. This traditional examination method is known as percussion. ”However, it is rarely used in modern medicine. "Instead, the patient often goes straight into the 'tube'." Images are often the means of choice in modern diagnostics.

“But sound also transmits important information from inside the human body,” emphasizes Razansky. “We have therefore adapted the traditional method of percussion with technologically highly sensitive devices such as laser beams and ultrasonic sensors. The informative value of the investigation is thereby expanded. "

Pictures without side effects

Ultrasound is a painless and quick way to examine organs and tissues. In contrast to multispectral optoacoustic tomography, however, it cannot display individual cells. Photoacoustics is the physical principle behind the new process. Here, too, images are generated, but the image information is provided by the sound. The sound waves are triggered by our body itself when laser impulses hit it and the light energy is converted into heat. The heating leads to a minimal expansion of the tissue. This generates signals - more precisely pressure waves - in the ultrasonic range. The acoustic signals generated in this way from the body are detected and converted into an image by a computer. Ntziachristos already sees great progress here for the patients: “Most imaging processes put a strain on the human body, for example with radiation or with administered contrast media. This is completely eliminated with photoacoustics. The laser impulses do not damage or stress human tissue. ”But the new process also has a lot to offer technically: Each tissue reacts differently to the laser impulses, depending on its light absorption. This creates individual and characteristic signal patterns that are typical for the respective tissue or for certain cells. “Even individual cells can be detected in this way, for example cancer cells. This is the big difference to ultrasound, which does not allow such a differentiation, ”describes Ntziachristos. Multispectral optoacoustic tomography currently works best with the very aggressive cancer cells of black skin cancer. But other cell types can also be differentiated on the basis of the sound pattern. “Surgeons will soon be able to check during a tumor operation whether they have actually been able to remove all cancer cells. It would, without a doubt, be another milestone in medical imaging. We have already achieved this in animal experiments. Initial human examinations also look very promising, ”emphasizes Ntziachristos.

Make the body's biochemistry visible

According to Ntziachristos, the development of the new process was by no means a sure-fire success: “The funding from the Federal Ministry of Education and Research helped us a lot,” says the researcher. “For many private investors, the risks were too high at the time.” In the meantime, the two scientists, together with other partners, have founded iThera Medical. "Our new process shows that health research can not only improve medical treatment, but also strengthen Germany as a location for innovation," explains Ntziachristos. The technology is also being further developed under the new roof, because there is no shortage of goals: “We want to go down to the level of molecules. What really interests us are the biochemical reactions of the cells, ”emphasizes Razansky. The team hopes to be able to detect diseases earlier and better track them. Future therapies could thus be better tailored to the respective person. This could improve the chances of recovery and, in the end, even lower health costs.

Multispectral Optoacoustic Tomography (MSOT)
The new process uses laser pulses to first generate sounds and then images of human tissue. The laser generates short flashes of light that penetrate the body. There the light is absorbed by the tissue. This happens to different degrees depending on the type of tissue and the wavelength of the laser pulses. The tissue expands due to the absorption of light and the associated minimal increase in temperature. These minimal movements generate acoustic signals. Each tissue generates characteristic and unique signals. For example, a blood cell produces a different signal than a skin cell. The different signals can be detected by ultrasound detectors on the skin surface. A computer then computes an image from the acoustic signals. The device should be ready for clinical use next year.

Contact Person:
Prof. Dr. Vasilis Ntziachristos
Technical University of Munich
Department of Biological Imaging
Ismaninger Strasse 22
81675 Munich
Tel .: 089 3187-3852
Fax: 089 3187-3008
Email: [email protected]