Reduction of background in optoacoustic image sequences obtained under tissue deformation

Abstract

For real-time optoacoustic imaging of the human body, a linear array transducer and reflection mode optical irradiation is preferably used. Experimental outcomes however revealed that such a setup results in significant image background, which prevents imaging structures at the ultimate depth limited only by the optical attenuation of the irradiating light and the signal noise level. Various sources of image background, such as bulk tissue absorption, reconstruction artifacts, and backscattered ultrasound, could be identified. To overcome these limitations, we developed a novel method that results in significantly reduced background and increased imaging depth. For this purpose, we acquire, in parallel, a series of optoacoustic and echo-ultrasound images while the tissue sample is gradually deformed by an externally applied force. Optoacoustic signals and background signals are differently affected by the deformation and can thus be distinguished by image processing. This method takes advantage of a combined optoacoustic/echo-ultrasound device and has a strong potential for improving real-time optoacoustic imaging of deep tissue structures.

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

“…Moreover, spectral OA imaging enables spatially-resolved measurement of the local blood oxygenation level, due to the different optical absorption spectra of oxygenated and deoxygenated hemoglobin thus providing both, structural as well as functional information [3][4][5][6]. The combination of OA imaging with conventional B-mode echo ultrasound (US) offers the potential of a multi-modal functional imaging modality [7][8][9][10][11]. The preferred setup for this modality is based on epi-mode, which implies that tissue irradiation and OA signal detection take place at the same tissue surface.…”

Determining the optical properties of a gelatin‑TiO_2 phantom at 780 nm

“…We opted for gelatin phantoms because they are relatively easy to produce and have the advantage of being adjustable to various purposes: (i) the phantom's optical properties can be customized by incorporating scattering agents (like TiO 2 or intralipid) or absorbing elements (like India ink, or any dye of interest), and (ii) the phantom's mechanical/elastic properties can be modified by varying the fraction of gelatin. Elastic properties especially play a valuable role: indeed, the combination of OA imaging with ultrasound elastography holds promise for reduced clutter and increased imaging depth in the framework of clinical imaging [6,7]. …”

Ultrasound-guided photoacoustic image reconstruction: image completion and boundary suppression

“…(13). A mask was created based on the normalized envelope of the simulated signals, setting to zero all data points in m l at which m sim;l exceeded a threshold value as a practical approximation to Eq.…”