Frequency Domian Optoacoustic Imaging

Two frequency domain optoacoustic imaging systems (frequency domain optoacoustic tomography system and frequency domain optoacoustic microscopy system) and three imaging modalities (traditional frequency domain optoacoustic imaging modality dependent on Chirp and other two newly developed imaging modalities named consecutive frequency mode and simultaneous frequency mode) based on these two imaging systems are introduced in this thesis. As a newly developed biomedical imaging method, optoacoustic or photoacoustic imaging has obtained a lot of attention during the past two decades, especially time-domain optoacoustic imaging. A brief introduction to the time domain optoacoustic imaging including tomography and microscopy is given. Comparing to time domain optoacoustic imaging, frequency domain optoacoustic imaging is quite young and has not been fully investigated. The most obvious difference between these two modalities is the energy source, for time domain optoacoustic imaging, a pulse laser is normally used and for frequency domain, a CW laser is applied which makes frequency imaging more economic and portable.The traditional frequency domain optoacoustic imaging modality which applies chirp to modulate the CW laser is a time-domain and frequency-domain mixed method, because it measures signals and frequencies as a function of time, and the reconstruction based on back-projection is done in time domain. Then consecutive frequency stimulation modality——a pure frequency domain method is proposed to compress the excitation time and a frequency domain model based algorithm is correspondingly developed.After demonstrating the feasibility of consecutive frequency stimulation modality, another new modality named simultaneous frequency stimulation modality is further proposed. As all the frequencies components are summed up and sent to the laser at the same time, the excitation time can be decreased. Due to the power limitation of our CW laser, the demonstration of this modality has been applied to microscopy.Analysis on the experimental results related to these three imaging modalities have are shown and it shows the simultaneous stimulation modality is a cost-efficient way to do frequency domain imaging.