In this paper, we developed a real-time dual-modality Photoacoustic (PA) /ultrasound (US) imaging system and performed initial clinical study, including both healthy and cancerous nodules. This dual-modality imaging system was based on a commercial US device (Resona7, Mindray Inc, China) modified to be capable to acquire PA signals without scarifying US functions. We also made special mechanical components to allow this handheld probe to perform 3D scanning dual-modality operation.
Optical excitation was provided by a tunable pulsed OPO (SpitLight 600 OPO, InnoLas Laser GmbH, Germany), which emits 7ns width pulses at 10Hz repetition rate. Light delivery was facilitated by a fiber bundle with bifurcated ends mounted on each axial side of a linear array transducer (L9-3U, Mindray Inc., China). The transducer consisted of 192 elements that were specially covered with a highly light scattering acoustic lens. Therefore, elements were mechanically focused 3cm beneath the surface of the lens in elevation direction and capable of detecting PA signals at frequencies of up to 7 MHz. The array was connected to the US machine to acquire and digitize all channel data in parallel. For optimal light coupling, a 7 mm-thick transparent soft gel pad was placed between the tissue surface and the probe. This pad provided a gap that allow light shining on the interested area just under the probe without sacrificing US imaging.
This dual-modal US machine can show both PA and US images (including B-scan and Doppler) simultaneously, as well as functional PA imaging. Our study demonstrated that PA imaging could provide important complementary information for traditional ultrasound examination, which has a great potential for clinical diagnosis of many diseases, including breast cancer and thyroid cancer.