Clinical demonstration of epi-mode photoacoustic clutter reduction using palpation scanning

Photoacoustic (PA) imaging, based on ultrasound detection after laser irradiation, is a promising extension to diagnostic ultrasound for vascular imaging and cancer diagnosis. For versatile use, epi-mode imaging with irradiation close to the acoustic probe is preferred. However, epi-mode results in strong clutter, limiting the imaging depth to typically less than two centimetres. It has previously been shown that clutter can be reduced in images acquired while palpating the tissue using the ultrasound probe. After motion compensation of the image sequence, averaging reduces decorrelating clutter and improves contrast. This method has now for the first time been applied to free-hand real-time clinical scans, and significant contrast improvement of clinical PA images was demonstrated.