For a circular scanning geometry in photoacoustic tomography, the axial/radial resolution is spatially invariant and is not affected by the ultrasound transducer (UST, detector) aperture. However, the tangential resolution is dependent on the detector aperture size and it varies spatially. Many techniques were proposed to improve the tangential resolution, such as attaching a concave lens in front of the nonfocused transducer or using a virtual point detector. Both of these methods have difficulties. Therefore, a modified delay-and-sum reconstruction algorithm has been proposed which can be used together with a standard ultrasound detector (nonfocused) to improve the tangential resolution. In this work, we validate the modified delay-and-sum algorithm experimentally for both flat and cylindrically focused USTs. More than threefold improvement in tangential resolution is observed. It is also shown that the object shape is recovered with this modified algorithm, which is very helpful for diagnosis and treatment purposes.

High-speed, low-cost, pulsed laser diode based second generation desktop photoacoustic tomography system

Four new N-ethylcarbazole-linked aza-boron-dipyrromethene (aza-BODIPY) dyes (8 a,b and 9 a,b) were synthesized and characterized. The presence of the N-ethylcarbazole moiety shifts their absorption and fluorescence spectra to the near-infrared region, λ≈650-730 nm, of the electromagnetic spectrum. These dyes possess strong molar absorptivity in the range of 3-4×10 m cm with low fluorescence quantum yields. The triplet excited state and singlet oxygen generation of these dyes were enhanced upon iodination at the core position. The core-iodinated dyes 9 a,b showed excellent triplet quantum yields of about 90 and 75 %, with singlet oxygen generation efficiency of about 70 and 60 % relative to that of the parent dyes. Derivatives 8 a,b showed dual absorption profiles, in contrast to dyes 9 a,b, which had the characteristic absorption band of aza-BODIPY dyes. DFT calculations revealed that the electron density was spread over the iodine and dipyrromethene plane of 9 a,b, whereas in 8 a,b the electron density was distributed on the carbazole group and dipyrromethene plane of aza-BODIPY. The uniqueness of these aza-BODIPY systems is that they exhibit efficient triplet-state quantum yields, high singlet oxygen generation yields, and good photostability. Furthermore, the photoacoustic (PA) characteristics of these aza-BODIPY dyes was explored, and efficient PA signals for 8 a were observed relative to blood serum with in vitro deep-tissue imaging, thereby confirming its use as a promising PA contrast agent.

No abstract

Mobile microrobots hold remarkable potential to revolutionize health care by enabling unprecedented active medical interventions and theranostics, such as active cargo delivery and microsurgical manipulations in hard-to-reach body sites. High-resolution imaging and control of cell-sized microrobots in the in vivo vascular system remains an unsolved challenge toward their clinical use. To overcome this limitation, we propose noninvasive real-time detection and tracking of circulating microrobots using optoacoustic imaging. We devised cell-sized nickel-based spherical Janus magnetic microrobots whose near-infrared optoacoustic signature is enhanced via gold conjugation. The 5-, 10-, and 20-μm-diameter microrobots are detected volumetrically both in bloodless ex vivo tissues and under real-life conditions with a strongly light-absorbing blood background. We further demonstrate real-time three-dimensional tracking and magnetic manipulation of the microrobots circulating in murine cerebral vasculature, thus paving the way toward effective and safe operation of cell-sized microrobots in challenging and clinically relevant intravascular environments.

Photoacoustic (PA) signals collected at the boundary of tissue are always band-limited. A deep neural network was proposed to enhance the bandwidth (BW) of the detected PA signal, thereby improving the quantitative accuracy of the reconstructed PA images. A least square-based deconvolution method that utilizes the Tikhonov regularization framework was used for comparison with the proposed network. The proposed method was evaluated using both numerical and experimental data. The results indicate that the proposed method was capable of enhancing the BW of the detected PA signal, which inturn improves the contrast recovery and quality of reconstructed PA images without adding any significant computational burden.

Applicability of optoacoustic imaging in biology and medicine is determined by several key performance characteristics. In particular, an inherent trade-off exists between the acquired field-of-view (FOV) and temporal resolution of the measurements, which may hinder studies looking at rapid biodynamics at the whole-body level. Here, we report on a single-sweep volumetric optoacoustic tomography (sSVOT) system that attains whole body three-dimensional mouse scans within 1.8 s with better than 200 m spatial resolution. sSVOT employs a spherical matrix array transducer in combination with multibeam illumination, the latter playing a critical role in maximizing the effective FOV and imaging speed performance. The system further takes advantage of the spatial response of the individual ultrasound detection elements to mitigate common image artifacts related to limited-view tomographic geometry, thus enabling rapid acquisitions without compromising image quality and contrast. We compare performance metrics to the previously reported whole-body mouse imaging implementations and alternative image compounding and reconstruction strategies. It is anticipated that sSVOT will open new venues for studying large-scale biodynamics, such as accumulation and clearance of molecular agents and drugs across multiple organs, circulation of cells, and functional responses to stimuli.

Photoacoustic tomography involves reconstructing the initial pressure rise distribution from the measured acoustic boundary data. The recovery of the initial pressure rise distribution tends to be an ill-posed problem in presence of noise and when limited independent data is available, necessitating regularization. The standard regularization schemes include, Tikhonov, 1 -norm, and total-variation. These regularization schemes weigh the singular values equally irrespective of the noise level present in the data. This work introduces a fractional framework, to weigh the singular values with respect to a fractional power. This fractional framework was implemented for Tikhonov, 1 -norm, and total-variation regularization schemes. Moreover, an automated method for choosing the fractional power was also proposed. It was shown theoretically and with numerical experiments that the fractional power is inversely related to the data noise level for fractional Tikhonov scheme. The fractional framework outperforms the standard regularization schemes, Tikhonov, 1 -norm, and totalvariation by 54% in numerical simulations, experimental phantoms and in vivo rat data in terms of observed contrast/signal-to-noiseratio of the reconstructed images.