Effect of irradiation distance on image contrast in epi-optoacoustic imaging of human volunteers

Abstract

In combined clinical optoacoustic (OA) and ultrasound (US) imaging, epi-mode irradiation and detection integrated into one single probe offers flexible imaging of the human body. The imaging depth in epi-illumination is, however, strongly affected by clutter. As shown in previous phantom experiments, the location of irradiation plays an important role in clutter generation. We investigated the influence of the irradiation geometry on the local image contrast of clinical images, by varying the separation distance between the irradiated area and the acoustic imaging plane of a linear ultrasound transducer in an automated scanning setup. The results for different volunteers show that the image contrast can be enhanced on average by 25% and locally by more than a factor of two, when the irradiated area is slightly separated from the probe. Our findings have an important impact on the design of future optoacoustic probes for clinical application.

In vivo dual-modality photoacoustic and optical coherence tomography imaging of human dermatological pathologies

“…Using a transducer array, both modalities can be integrated in a handheld probe. While photoacoustic imaging visualizes vessels up to 10 mm depth from the surface of the skin, ultrasound B-mode imaging visualizes anatomical parts such as bone and fascia [17]. However, in their combined system, due to the lack of contrast of ultrasound imaging, the morphology of the skin cannot be visualized.…”

Photoacoustic clutter reduction by inversion of a linear scatter model using plane wave ultrasound measurements

“…Due to the high fluence at the irradiation area on the skin surface and the strong absorption of melanin in human skin, the amplitudes of the reflected clutter waves can overcome the amplitudes of the waves carrying the desired signal information. In general, direct PA waves cannot easily be distinguished from clutter waves, which is a severe detriment on the validity of images that suffer from clutter artifacts [5,6].…”

“…However, the desired inplane irradiation is usually problematic, due to even stronger clutter amplitudes. These cause the irradiation position with maximum contrast to be shifted away from the transducer, if clutter is not corrected for [5,6]. The approach presented here focuses on setups with in-plane irradiation.…”

Identification and elimination of reflection artifacts in biomedical photoacoustic imaging

“…The use of the frequency-domain approach permits reconstruction and presentation of the resultant image in real-time, a key criterion for a PA system developed around a US scanner. Several groups have reported on fast algorithms based on frequency domain processing [26,27]. Systems have been presented that can do real time reconstruction of PA images [28][29][30], and some others based on recent developments in GPU technology which can do real-time PA and US imaging [14].…”

“…The first report of a combined PA-US system using a handheld probe was from the Bern group [27] in collaboration with the Fraunhofer Institute (St. Ingbert, Germany). A custom made high-speed US system was developed that could simultaneously perform PA imaging.…”