4 March 2013 Simultaneous multispectral coded excitation using periodic and unipolar M-sequences for photoacoustic imaging
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Abstract
Photoacoustics (PA) enables optical-absorption imaging such as functional imaging with depth information by combining ultrasonics and optics. The issue with PA is to increase the signal-to-noise ratio (SNR) because excitation light is attenuated with depth. Repeating irradiation degrades the frame rate, and it will be worse to acquire multispectral information. In previous research, we proposed the m-sequence family such as gold codes, which provide better SNR images than the ensemble average. However, the sending procedure is so complex that it was essential to send sequences twice aperiodically since the negative codes of bipolar sequences must be sent separately, and the decoding artifacts of those bipolar sequences cannot be minimized in aperiodic sending, unlike periodic sending. This study proposes periodic and unipolar m-sequences (PUM): a unipolar sequence consisting of {1, 0}, selected from positive codes of bipolar msequences. Signals can be enhanced by decoding periodically sent PUM using bipolar sequences, and there are no coding artifacts at all for a single wavelength. Moreover, in multispectral simultaneous irradiation, the crosstalk in PUM remains low, which is inherited from m-sequences. We demonstrated that PUM’s improved SNR is superior to that of aperiodic m-sequence family codes or orthogonal Golay codes. Furthermore, the frame-rate, which is normally limited by acoustic time-of-flight, can be maximized up to the pulse repetition frequency since the decoding start point can be set in any code in periodic irradiation.
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Haichong Zhang, Kengo Kondo, Makoto Yamakawa, Tsuyoshi Shiina, "Simultaneous multispectral coded excitation using periodic and unipolar M-sequences for photoacoustic imaging", Proc. SPIE 8581, Photons Plus Ultrasound: Imaging and Sensing 2013, 85812Y (4 March 2013); doi: 10.1117/12.2003319; https://doi.org/10.1117/12.2003319
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