Contact-free photoacustic imaging of tissue for endoscopic applications by speckle vibration analysis

• Applicant: Dr.-Ing. Florian Klämpfl
• Subject Area: Measurement Systems ; Joining and Separation Technology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 397972545

When surgical scalpels are used, perforation and injury to important tissue structures can occur in addition to severe bleeding and inflammation in the treatment area. A surgical instrument that does not have these inherent dangers would be desirable to minimize risk. The use of a laser is a conceivable alternative here. To date, however, this minimally invasive laser application has one main disadvantage compared to a classic scalpel: the lack of depth information during the procedure. Damage to essential tissue structures (blood vessels, nerves, muscle tissue) through the use of the laser cannot be ruled out. Therefore, a feedback system is needed that provides structural depth information and thus enables the treating physician to improve orientation during laser interventions. Photoacoustic tomography (PAT) is introduced in this project application as the optimal modality to fulfill these requirements. Specifically, the proposal focuses on non-contact photoacoustic speckle vibration analysis. This technique has been successfully researched at the Institute of Photonic Technologies for a long time. In the planned research project, the work of the previous project is to be continued and, on the one hand, the points mentioned in the outlook of the predecessor project and, on the other hand, newly arising research questions are to be addressed. So far it could be shown that it is in principle possible to realize a non-contact photoacoustic depth feedback system by means of speckle vibration analysis. The aim of the present project is now to show that it is possible to achieve clinically relevant resolutions in the range of a few µm by using non-contact photoacoustic speckle vibration analysis. It is also important to miniaturize the system. The aim is to scan a field of 4x4 surface points through a fiber bundle with a frequency of 10 MHz, whereby the MZB values (max. permissible irradiation) for tissue should not be exceeded. Based on this, the absorber structure should be reconstructed as best as possible. To achieve these goals, new approaches to increase spatial and temporal resolution as well as reconstruction are necessary. A fundamental challenge to be solved is the trade-off between spatial and temporal resolution, as well as the sensitivity of the imaging system in capturing the speckle pattern. The vision of the research project continues to be the development of an automated and safe laser scalpel to build a foundation for the use of the laser as a surgical tool during endoscopic procedures. In addition, it is conceivable in the long term to implement a non-contact photoacoustic-based mammography procedure that does not require any ionizing radiation.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Michael Schmidt