Real-time pulse echo and photoacoustic imaging using an ultrasound array and in-line reflective illumination

Recent clinical studies have demonstrated that photoacoustic (PA) imaging, in conjunction with pulse echo (PE) ultrasound is a promising modality for diagnosing breast cancer. However, existing devices are unwieldy and are hard to integrate into the clinical environment. In addition, it is difficult to illuminate thick samples because light must be directed around the transducer. Conventional PA imaging designs involve off-axis illumination or transillumination through the object. Whereas transillumination works best with thin objects, off-axis illumination may not uniformly illuminate the region of interest. To overcome these problems we have developed an attachment to an existing clinical linear array that can efficiently deliver light in line with the image plane. This photoacoustic enabling device (PED) exploits an optically transparent acoustic reflector to co-align the illumination with the acoustic waves, enabling realtime PA and PE imaging. Based on this concept, we describe results from three types of PEDs in phantoms and rat tissue. The most recent version is fabricated by rapid prototyping, and attached to a 10 MHz linear array. Real-time PA and PE images of a 127-μm diameter wire were consistent with our expectations based on the properties of the ultrasound transducer. Comparisons with and without the PED of another test phantom printed on transparency demonstrated that the PED does not appreciably degrade or distort image quality. The PED offers a simple and inexpensive solution towards a real-time dual-modality imaging system for breast cancer detection. It could also be adapted for virtually any kind of ultrasound transducer array and integrated into routine ultrasound exams for detection of cancerous lesions within 1-2 cm from the probe surface.