Real-time improvement of LED-based photoacoustic image quality using intermittent pulse echo acquisitions

Photoacoustic imaging is a hybrid modality with advantages of both the ultrasound and optical imaging. This technique with optical spectroscopic contrast and acoustic resolution holds promise in wide range of clinical and preclinical applications. Since photoacoustic imaging also involves ultrasound detection, it is straight forward to implement pointof- care dual mode systems with capability of structural and functional imaging. High signal generated from skin-melanin layer is an important problem in any handheld reflection-mode photoacoustic probes. This problem caused by high light fluence just beneath the ultrasound probe results in reduction of vascular contrast and also causes difficulty in image interpretation. In this work, using our LED-based photoacoustic and ultrasound imaging system (AcousticX), we demonstrate the potential of using ultrasound acquisitions dynamically to suppress high photoacoustic signal from skin surface and qualitatively improve the image contrast and quality. In AcousticX, photoacoustic and conventional pulseecho acquisitions are performed in an intermittent manner resulting in a dual-mode display frame rate of 30 Hz. We make use of the line-by-line/planewave ultrasound acquisitions to automatically delineate the skin surface in quasi realtime and suppress photoacoustic signal from the identified area, resulting in improved image interpretation and contrast without losing temporal resolution. Real-time 2D and 3D (linear scan) imaging experiments were performed on finger and foot dorsum of healthy human volunteers to validate the new skin-signal suppression technique. Results give a direct confirmation that our ultrasound-assisted skin-signal reduction feature holds strong potential in enhancing vascular contrast and visual quality in real-time 2D and 3D LED-based photoacoustic imaging.