Development and experimental validation of methods for quantitative photoacoustic tomography of blood oxygen saturation in vivo

• Applicants: Professor Jan Laufer, Ph.D.; Dr. Steffen Prohaska
• Subject Area: Medical Physics, Biomedical Technology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268705117

Photoacoustic (PA) tomography is an emerging biomedical imaging modality in which the absorption of short optical pulses by tissue chromophores is used to generate broadband ultrasonic waves. These waves propagate to the skin where time-resolved PA signals are detected by transducer arrays. From these signals, high resolution (tens of microns) 3-D images are then obtained using image reconstruction algorithms. Since the main tissue absorber in the visible and near-infrared wavelength region is haemoglobin, these images typically represent the vasculature. PA imaging combines a number of powerful attributes, such as multiscale imaging capabilities and strong contrast in vascularised soft tissues due to the absorption by haemoglobin where other modalities, such as MRI, x-ray CT, and ultrasound lack sensitivity. Its most powerful attribute is the potential for making spatially resolved measurements of absolute chromophore concentrations and derived parameters, such as blood oxygen saturation, which is essential for physiological and molecular imaging applications. However, this potential has yet to be harnessed. Deep tissue 3-D quantitative PA tomography in particular remains highly challenging due to the scale of the inverse problem, and has not been demonstrated in vivo to date. To translate PA tomography to a broad range of applications in the life sciences, the development of accurate and reliable methods for the solution of the inverse problem of qPAT is required. The aim of this project is the development and experimental validation of practicable methods for determining the absolute blood oxygen saturation from in vivo multiwavelength 3-D PA tomography images. The challenges that will be addressed are 1) the development of an efficient 3-D PA forward model, 2) the development of computational and experimental methods for a tractable model-based inversion, 3) the experimental validation of practicable methods for the measurement of blood oxygenation in tissue phantoms, and 4) experimental validation in vivo in a small animal model of tissue regeneration. This project will deliver the first experimentally validated methodology for the non-invasive measurement of absolute blood oxygenation in deep tissue, a major step towards the application of quantitative PA tomography in the life sciences. In addition, the knowledge gained during this project is expected to contribute substantially to the long-term development of quantitative methods for molecular PA tomography.

• DFG Programme: Research Grants
• Major Instrumentation: OPO laser system
• Instrumentation Group: 5700 Festkörper-Laser