Real-Time Photoacoustic and Ultrasound Imaging: A Simple Solution for Clinical Ultrasound Systems with Linear Arrays

Recent clinical studies have demonstrated that photoacoustic imaging (PAI), in conjunction with pulse echo ultrasound, is a promising modality for diagnosing breast cancer. PAI relies on the absorption of a short laser pulse followed by transient heating, thermoelastic expansion, and generation of ultrasonic waves. An ultrasound transducer then detects these waves to produce an image with optical contrast. In tissue, optical contrast differentiates vasculature, which can assist radiologists in diagnosing a lesion. However, current PAI setups use expensive complex hardware and inefficiently illuminate the image, limiting its practicality for preclinical and clinical research. An ideal PAI platform would be compatible with commercial ultrasound systems, light efficient, and inexpensive, while complementing ultrasonography. We designed and fabricated an accessory to a linear ultrasound array. It exploits an optically transparent acoustic reflector to couple laser illumination into the imaging plane of the transducer. The device’s optical and acoustic transmission properties were compared to the performance of common fiber bundle dark-field illumination in a tissue-mimicking phantom. The attachment also imaged an in vivo mouse model of a human pancreatic tumor in real-time. The photoacoustic signal in a scattering medium exhibited a 6 dB enhancement 20 mm deep. Furthermore, PAI of the pancreatic tumor exhibited >11 dB optical absorption compared to surrounding tissue 3 mm deep, while the pulse echo ultrasound provided an anatomical reference. This design offers an inexpensive solution to deliver superior illumination for facilitating dual modality imaging using existing ultrasound hardware. It could accelerate the translation of this technology into clinical practice.