Figure 1

System for all-optical ultrasound imaging through a needle (a). The sharp inner needle (schematic and inset photo) used to puncture the cardiac septum to gain access to the left atrium can be safely recessed within a blunt outer needle cannula. After puncturing, the dilator sheath is advanced over the needle into the left atrium. The probe includes two optical fibers positioned within the inner needle for pulse-echo ultrasound imaging: one for transmission (Tx) with the delivery of pulsed excitation light to an optically absorbing coating and one for reception (Rx) with the delivery of continuous-wave (CW) light to a Fabry–Pérot cavity. Acoustic isolation between the Tx and Rx fibers is provided by a thin metal septum. Scale bar, 500 μm. The corresponding console (b) delivers pulsed excitation to the Tx fiber and CW light from a wavelength-tunable laser to the Rx fiber. Reflections from the Rx fiber are detected with a photoreceiver (PR) through an optical circulator. Low-frequency PR signals are used to determine the optimal wavelength tuning of the CW laser; high-frequency PR signals are processed to generate ultrasound images and are displayed in real-time. Spatially resolved transmitted ultrasound as measured in a plane parallel to the optical fiber axis (c) had a divergence angle (FWHM) of 23° (dashed-dotted white lines). The divergence was smaller (15.2°) for frequencies of 20–40 MHz (short dashed white lines) and larger (29.9°) for frequencies of 2.5–20 MHz (long dashed white lines). Spatially resolved transmitted ultrasound measured in a plane perpendicular to the optical fiber axis 1.5 mm from the fiber tip (green dashed lines in c) was circularly symmetric (d). Time-resolved transmitted ultrasound measured on-axis at 1.5 mm from the fiber tip was predominantly bipolar (e) with a broad bandwidth (−6 dB) of 26.5 MHz (f). DAQ, data acquisition; DAQ H, DAQ for high-frequency PR signal; DAQ L, DAQ for low-frequency PR signal; GPIB, general purpose interface bus; TRIG, trigger.