Improved contrast deep optoacoustic imaging using displacement-compensated averaging: breast tumour phantom studies

Abstract

For real-time optoacoustic (OA) imaging of the human body, a linear array transducer and reflection mode optical irradiation is usually preferred. Such a setup, however, results in significant image background, which prevents imaging structures at the ultimate depth determined by the light distribution and the signal noise level. Therefore, we previously proposed a method for image background reduction, based on displacement-compensated averaging (DCA) of image series obtained when the tissue sample under investigation is gradually deformed. OA signals and background signals are differently affected by the deformation and can thus be distinguished. The proposed method is now experimentally applied to image artificial tumours embedded inside breast phantoms. OA images are acquired alternately with pulse-echo images using a combined OA/echo-ultrasound device. Tissue deformation is accessed via speckle tracking in pulse echo images, and used to compensate in the OA images for the local tissue displacement. In that way, OA sources are highly correlated between subsequent images, while background is decorrelated and can therefore be reduced by averaging. We show that image contrast in breast phantoms is strongly improved and detectability of embedded tumours significantly increased, using the DCA method.

Real-time clinical clutter reduction in combined epi-optoacoustic and ultrasound imaging

“…One of the reasons is that compressive deformation is more likely to result in out-of-plane motion at slippery interfaces between e.g., muscle epimysia, or between glands and surrounding tissue. The other reason is that echo clutter tends to move at a similar speed as true signals in compression mode, whereas the displacement rate is roughly half the displacement rate of true signals in shear mode [29]. Therefore shear deformation will allow for more efficient separation between true signal and echo clutter.…”

“…In combined OA and US imaging, motion tracking of US images provides the knowledge of local tissue displacement that is required for OA deformation compensation. In-vitro tissue [28] and gelatin phantom [29] studies, having realistic echogenicity in addition to the optical properties, have consistently shown that DCA significantly improves imaging depth in comparison to conventional averaging without probe motion. These experiments were performed with controlled probe motion using motorized stages.…”

“…Unfortunately, a suitable clinical imaging depth has up to date been hard to achieve with epi-OA imaging. The main reason is that epi-OA imaging contrast is limited in addition to thermal noise by significant clutter [15,[27][28][29]. This clutter is thought to arise from strong OA transients that are generated at the site of tissue irradiation, and are detected (i) after direct propagation to the imaging probe (direct clutter), or (ii) after being scattered by acoustic inhomogeneities located within the imaging plane (echo clutter).…”

Imaging technique for real-time temperature monitoring during cryotherapy of lesions

“…% phantoms with 2 mg∕mL of methylparaben added as a preservative. 42 The gelatin phantom matrix was enriched with scattering and absorbing properties produced by titanium dioxide powder (KAI Tech Labs) and a suspension of gold nanorods (GNRs) made in our laboratory. At the laser wavelength of 805 nm, GNRs, homogeneously distributed in the phantoms, provided optical absorbance μ a ≈ 0.2 cm −1 .…”

Hybrid photoacoustic and ultrasound section imaging with optical ultrasound detection

“…The perfect overlap of PA and US images is essential for being able to take advantage of the complementary contrast mechanisms. Moreover, this also allows for using US imaging information for improvements of the PA image, such as in displacement compensated averaging [6]. Hybrid PA/US imaging devices have also been demonstrated for intravascular imaging, using an imaging catheter [7].…”