Low frequency detection in clinical multispectral optoacoustic tomography

Frequency response characterization of optoacoustic (photoacoustic) detectors is critical because the signals are broadband, and the center frequency relates to the absorber size. We were particularly interested in studying the sub-1 megahertz response, which enables imaging of low spatial frequencies associated with resolving organs up to centimeter size. State-of-the-art characterization methods fail to measure this kilohertz frequency response reliably, leading to an incomplete understanding of the largest structures captured in an optoacoustic image. Herein, we developed an experimental arrangement to identify the lowest measurable frequency of an optoacoustic detector. We observe that a common optoacoustic detector with a 3.4 megahertz center frequency and 72 % 3 dB bandwidth can capture signals as low as 75 kilohertz. Given insufficient characterization methods, we also investigate artifacts triggered by image reconstruction with an erroneous kilohertz frequency response. Collectively, our work discusses the impact of incorporating low frequencies on optoacoustic image fidelity.