See starving tissues
Zones of acute hypoxia (oxygen starvation) are formed in diseases such as fast-growing tumors, complete or partial blockage of blood vessels (stroke or peripheral artery disease). A group of scientists from the University of Illinois, led by Jefferson Chan, has developed a non-invasive method for identifying hypoxia sites in real time.
For this purpose, oxygen-sensitive molecules were used, which emit ultrasonic signals when exposed to light during hypoxia. The method based on the work of photoacoustic molecules was called optical-acoustic tomography.
In a study on mice, scientists demonstrated the possibility of optical-acoustic tomography to visualize areas of hypoxia in tumors and arterial occlusion. The advantages of this method are its non–invasiveness and relative cheapness in comparison with the currently approved positron emission tomography (PET).
The developed method can in real time give a three-dimensional image of areas of organs experiencing hypoxia, so that the doctor can coordinate actions during surgery or adjust the prescribed treatment.
Existing methods for detecting hypoxia in tissues are able to detect only a chronic process, they are not able to help doctors identify acute hypoxia (for example, stroke) or aggressive rapidly growing tumor – those conditions that require immediate intervention. The use of radioactive drugs in combination with PET is currently the only way to detect acute hypoxia, but this method is not accurate enough. In addition, the introduction of radioactive drugs into the body carries a known risk of complications.
Conducting optical-acoustic tomography does not require intervention in the human body, that is, the method is not invasive. The molecular probes of the Chan group are activated only under hypoxia conditions. The method is based on the phenomenon of photoacoustics, in which light falling on molecules causes their excitation and triggers a chain of reactions, as a result of which the light wave is transformed into a sound wave. Capturing the latter allows you to build a three-dimensional image.
The estimated cost of the procedure will be much lower than PET: as the authors write, it is enough to simply equip the existing ultrasound diagnostic device with a light source – LED lamps. The introduction of photoacoustic molecules can be performed both into the general bloodstream by intravenous injection, and directly into the tumor area.
Photoacoustic molecules required for optical-acoustic tomography will be inexpensive and can be stored for a long time: they can remain stable for several years. For comparison, radioactive preparations should be used immediately after manufacture and only after special preparation.
The system was tested on mouse models of breast cancer and occlusion of the arteries of the lower extremities.
The method of optical-acoustic tomography is able to detect ischemia already a few minutes after the violation of blood flow. This opens up impressive prospects for the diagnosis of stroke or acute thrombosis of another localization. In mice with breast cancer, the described method gave a detailed three-dimensional ultrasound image of the tumor.
In cancer research, attention is often focused on the development of treatment methods based on whether or not hypoxia is present in the tumor. Opto-acoustic tomography will replenish the arsenal of researchers with a non-invasive method for detecting hypoxic tumors.
The authors of the study continue to study photoacoustic molecules. Of particular interest are those that can be oncospecific and indicate the depth of germination and localization of tumor spread.
Article by Hailey J. Knox et al. A bioreducible N-oxide-based probe for photoacoustic imaging of hypoxia is published in the journal Nature Communications.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of the Illinois News Bureau: Molecular beacon signals low oxygen with ultrasound.