서강대학교

초록/요약

Photoacoustic (PA) imaging based on PA effect is a hybrid functional imaging modality that combines strong optical contrast with high ultrasonic spatial resolution. It showed great potentials in diagnosis of cancer due to its high extrinsic optical contrast such as hemoglobin and melanin. In PA imaging, non-ionizing laser energy is delivered in biological tissue and acoustic waves (i.e., PA signals) are generated only inside a target that absorbs the incident laser pulses due to thermo-elastic expansion. The PA signals are detected by an ultrasound (US) transducer and then an image of initial pressure distribution is reconstructed. Among various PA imaging system configurations, the cross-sectional PA imaging can provide real-time imaging and be used in clinical applications with minimal modification of a current ultrasound (US) scanner. However, a suitable image reconstruction method for the cross-sectional PA imaging was not investigated and a reconstruction method used in US imaging was employed. Thus, to fully take advantages of PA imaging and widely accepted in clinical practice, an adequate reconstruction method for the cross-sectional PA imaging should be explored In this thesis, we have developed new beamforming methods for enhancing image quality of PA imaging based on a commercial one-dimensional (1D) array transducer. First, for precise calculation of time-of-flight, a method for estimating optimal sound speed was developed. Since the method could minimizes the phase distortion stemming from disparity between a true sound speed and assumed one in beamformation, the best beamforming performance was achieved, leading to improvement of the lateral resolution and signal-to-noise ratio (SNR). In addition, adequate image reconstruction method for PA imaging, i.e., display pixel based focusing (DPBF), was proposed with viable computational complexity. The method was further extended to three-dimensional (3D) imaging, i.e., display voxel based focusing (DVBF). In the method, poor elevational resolution poor elevation resolution due to the fixed focusing by an acoustic lens was retrieved by using synthetic aperture technique. For this, mathematical analysis was performed and appropriate synthetic focusing delay was proposed. The developed methods were evaluated through simulation, in vitro, and ex vivo experiments with microcalcification contained breast specimens. From the results, it was learned that the proposed method can enhance the image quality of PA imaging based on a 1D array transducer and may useful for the clinical use.