Ring-segment piezopolymer sensor optimized for cylindrical-wave detection in optical-resolution optoacoustic angiography with extended imaging depth

Optical resolution optoacoustic (or photoacoustic) microscopy (OR-OAM) utilizing a 532 nm laser wavelength represents a promising approach for non-invasive visualization of superficial hemoglobin-rich structures. However, clinical translation of OR-OAM angiography typically faces a trade-off between achieving high contrast and resolution versus maintaining an extended depth-of-field at safe laser exposure levels. Gradient refractive index (GRIN) fiber lenses can provide an elongated optical focus preserved over a millimeter-scale length. However, developing coaxially aligned wideband acoustic detectors with high sensitivity remains challenging. Here, we introduce a piezopolymer PVDF-TrFE detector featuring a spherically-focused thin (100 μm) ring geometry with a 4.6 mm aperture and 1.5 mm working distance (NA = 0.84). Numerical modeling reveals not only an extended depth of field, but also an improvement in sensitivity compared to conventional full-aperture detectors. In vitro experiments using whole human blood demonstrated a 14 dB signal-to-noise ratio at a safe laser irradiance of 20 mJ/cm. In vivo angiographic imaging of neonatal mouse cerebral vasculature and human cuticle confirmed the detector's capability to achieve a depth-of-field exceeding 1 mm, highlighting its potential for a broad range of biomedical applications.