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Emerging evidence indicates crosstalk between the brain and the hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) mouse model that is widely used in focal cerebral ischemia research. Naïve, sham and tMCAO mice underwent positron emission tomography (PET) using [18F]fluorodeoxyglucose (FDG) for assessing glucose metabolism and multispectral optoacoustic tomography (MSOT) assisted with quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in the peripheral tissues at 24 h after reperfusion. We found increased levels of [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. A positive correlation was observed between splenic and ipsilateral striatal [18F]FDG uptake. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to a significant increase in the numbers of mature T cells (CD4 and CD8) in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and their decrease in peripheral blood. The numbers of mature granulocytes (determined as CD11b+Gr1hi cells) decreased in bone marrow tissues and blood but increased in the spleen. The combination of quantitative PET and MSOT thus enabled the observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.

Acoustic-resolution optoacoustic microscopy (AR-OAM) visualizes internal tissue structures at millimeter to centimeter scale depths with high spatial resolution. The imaging performance mainly depends on the geometry and detection characteristics of the ultrasound transducer. Reconstruction methods incorporating transducer effects are essential to optimize achievable resolution, contrast and overall image quality. Model-based (MB) reconstruction has been shown to provide excellent imaging performance in several optoacoustic embodiments, due to its capacity to accurately model the transducer. However, the applicability of MB reconstruction methods in AR-OAM has been hampered by the high computational cost. Here, we propose an efficient MB reconstruction framework for largescale AR-OAM by considering scanning symmetries, which enabled capitalizing the computational power of a graphics processing unit. The suggested MB reconstruction method is shown to significantly improve the imaging performance of AR-OAM compared to synthetic aperture focusing technique, as validated in in vivo mouse skin experiment.

Optoacoustic tomography based on insufficient spatial sampling of ultrasound waves leads to loss of contrast and artifacts on the reconstructed images. Compared to reconstructions based on L2-norm regularization, sparsity-based reconstructions may improve contrast and reduce image artifacts but at a high computational cost, which has so far limited their use to 2D optoacoustic tomography. Here we propose a fast, sparsity-based reconstruction algorithm for 3D optoacoustic tomography, based on gradient descent with Barzilai-Borwein line search (L1-GDBB). Using simulations and experiments, we show that the L1-GDBB offers fourfold faster reconstruction than the previously reported L1-norm regularized reconstruction based on gradient descent with backtracking line search. Moreover, the new algorithm provides higher-quality images with fewer artifacts than the L2-norm regularized reconstruction and the back-projection reconstruction.

Lack of sensory feedback during laser surgery prevents surgeons from keeping track of the exact lesion profile and cutting depth. As a result, duration and complexity of the treatments are significantly increased. In this study we propose a new method for enabling three-dimensional tracking of the exact lesion profile, based on detection of shock waves emanating from the ablated tissue and subsequent reconstruction of the incision location using time-of-flight data obtained from multiple acoustic detectors. Ablation was performed in fresh bovine tissue samples using a Q-switched Nd-YAG laser, delivering 8 ns duration 150mJ pulses at a wavelength of 1064nm and repetition rate of 5Hz. The beam was focused by a 50mm lens on the tissue surface, which resulted in a deep cut of up to 9mm depth. The generated shock waves were detected using a spherical matrix ultrasonic array. The exact cutting profile was subsequently rendered by reconstructing the origin of shockwaves detected during the entire procedure. Different combinations of the detector positions were considered with respect to the resulting reconstruction quality. It was observed that, by utilizing at least 12 detection elements, the lesion profile could be characterized with high accuracy in all three dimensions, which was confirmed by histological evaluations. The proposed method holds promise for delivering highly precise and accurate real-time feedback during laser surgeries.

Image quality in 3-D optoacoustic (photoacoustic) tomography is greatly influenced by both the measurement system, in particular the number and spatial arrangement of ultrasound sensors, and the ability to account for the spatio-temporal response of the sensor element(s) in the reconstruction algorithm. Herein we present a reconstruction procedure based on the inversion of a time-domain forward model incorporating the spatial impulse response due to the shape of the transducer, which is subsequently applied in a tomographic system based on a translation-rotation scan of a linear detector array. The proposed method was also adapted to cope with the data-intensive requirements of high-resolution volumetric optoacoustic imaging. The processing of 2 · 10 (4) individual signals resulted in well-resolved images of both ~ 200 μm absorbers in phantoms and complex vascular structures in biological tissue. The results reported herein demonstrate that the introduced model-based methodology exhibits a better contrast and resolution than standard back-projection and model-based algorithms that assume point detectors. Moreover, the capability of handling large datasets anticipates that model-based methods incorporating the sensor properties can become standard practice in volumetric opto acoustic image formation.