Coded excitation for photoacoustic imaging using a high-speed diode laser

Area of Science:

• Biomedical Optics
• Acoustic Imaging
• Laser Physics

Background:

• Traditional Q-switched Nd:YAG lasers for photoacoustic (PA) imaging are bulky and expensive.
• Diode lasers offer higher pulse repetition frequencies but typically lack sufficient energy for effective PA generation.
• Existing methods for enhancing diode laser PA signals involve coded pulses and compression, but often require complex stimuli.

Purpose of the Study:

• To investigate a novel coded excitation method using diode lasers for biomedical photoacoustic (PA) applications.
• To improve the signal-to-noise ratio (SNR) in PA signal detection using frequency-coded laser pulses.
• To assess the effectiveness of this method compared to existing techniques, particularly in reducing the need for complex pulse sequences.

Main Methods:

• Employed a diode laser system with frequency-coded excitation, tuning the interval between adjacent laser pulses.
• Utilized a 20-MHz PA transducer for backward-mode PA detection.
• Generated frequency-coded PA signals and analyzed the SNR of the decoded signal.
• Investigated the reduction of range side lobes through compression filter optimization.

Main Results:

• The frequency-coded PA signal generation improved the SNR of the decoded PA signal by up to 19.3 dB.
• High range side lobes were observed in the decoded signal.
• Optimization of the compression filter was shown to reduce these side lobes.
• The proposed coded excitation method requires only a single stimulus, unlike Golay codes.

Conclusions:

• The developed frequency-coded excitation method offers a significant SNR improvement for PA imaging using diode lasers.
• This approach provides a more practical and potentially cost-effective alternative to traditional laser sources for PA applications.
• Further optimization of compression filters is recommended to mitigate side lobe artifacts and enhance image quality.