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We introduce a novel experimental design for non-invasive scanning optoacoustic microscopy that utilizes a parabolic surface for ultrasound focusing. We demonstrate that off-axis parabolic mirrors made of sufficiently high acoustic impedance materials work as ideal reflectors in a wide range of apertures and provide lossless conversion of a spherical acoustic wavefront into a plane wave. We further test the performance of a custom optoacoustic imaging setup which was developed and built based on these principles. The achieved resolution limit of 0.3 mm, with NA of 0.5 and the transducer bandwidth of 5 MHz, matches the resolution limit defined by diffraction. Although further improvements of current experimental setup are required to achieve resolution similar to leading microscopy systems, this proof-of-concept work demonstrates the viability of the proposed design for optoacoustic microscopy applications.

We used a three-dimensional optical tomogaphy system that was previously developed to create high contrast maps of optical absorbance of mice tissues. In this study, animals were scanned before and after injection of gold nanorods (GNRs) at different time periods. As-synthesized GNRs were purified from hexadecyltrimethylammonium bromide (CTAB) and coated with polyethylene glycol (PEG) to obtain GNR-PEG complexes suitable for in vivo applications. Intravenous administration of the purified GNR-PEG complexes to mice resulted in an enhanced contrast of normal tissues and blood vessels as compared to ordinary nude mice. In parallel with optoacoustic imaging we investigated the accumulation of GNRs in liver using invasive analytical techniques. Maximum levels of GNRs in liver macrophages were observed after 48-72 hours post-injection, followed by slow clearance trend after 8 days. Optoacoustic imaging revealed redistribution of GNR in mouse organ and tissues: in the initial hours, accumulation of GNRs is seen predominantly in the periphery of the mouse, while a gradual increase of GNR levels in liver, spleen and kidneys is seen in 1 and 24 hours.

SEVERAL investigators have suggested extrarenal sources of renin, particularly in the uterus1,2and the salivary glands3,4. Nasjetti et al.5could stimulate renin from extra-renal sources in nephrectomized rats, and Capelli et al.6reported increasing plasma renin activity in anephric humans with prolongation of the post-nephrectomy period.

We report on the optoacoustic (OA) imaging of the whole mouse body using a biocompatible contrast agent - highly purified, pegylated gold nanorods (GNR) - which has strong optical absorption in the near-infrared region and low level of toxicity. In vitro toxicity studies showed no significant change in survival rates of the cultured normal epithelium IEC-6 cells when incubated for 24 hours with up to 1 nM of GNR. In vivo toxicity studies in nude mice showed no pathological changes in liver 1 month after the IV injection of GNR with intra-body concentration around 0.25-0.50 nM. In order to study the enhancement of the OA contrast and accumulation of GNR in different tissues, we performed 3D OA imaging of live nude mice with IV-injected GNR. The enhancement of the OA contrast in comparison with the images of the untreated mice was visible starting 1 hour after the GNR injection. The OA contrast of kidneys, liver, and spleen peaked at about 2-3 days after the administration of the GNR, and then was gradually reducing.

Coregistered optoacoustic (OA) and ultrasound (US) images obtained using a dual modality optoacoustic/ultrasonic breast imaging system are used together for enhanced diagnostic capabilities in comparison to each individual technology. Therefore, an operator-independent delineation of diagnostically relevant objects (in our case breast tumors) with subsequent automatic analysis of image features is required. We developed the following procedure: 1) Image filtering is implemented on a US image to minimize speckle noise and simultaneously preserve the sharpness of the boundaries of the extended objects; 2) Boundaries of the objects of interest are automatically delineated starting with an initial guess made by an operator; 3) Both US and OA images are analyzed using the detected boundaries (contrast, boundary sharpness, homogeneity of the objects and background, boundary morphology parameters are calculated). Calculated image characteristics can be used for statistically independent evaluation of structural information (US data) and vascularization (OA data) of the studied breast tissues. Operator-independent delineation of the objects of interest (e.g. tumors and blood vessels) is essential in clinical OA spectroscopy (using multiple laser wavelengths to quantify concentrations of particular tissue chromophores, such as oxy- and deoxy- hemoglobin, water, and lipids). Another potential application of the suggested image analysis algorithm could be in OA imaging system design, when system performance should be evaluated in terms of quality of the images reconstructed from the well-defined objects of interest. The discussed principles of image analysis are illustrated by using real clinical US and OA data.