Two-Dimensional Photoacoustic/Ultrasonic Endoscopic Imaging Based on a Line-Focused Transducer

Existing acoustic-resolution photoacoustic/ultrasonic endoscopy (PA/USE) generally employs a point-focused transducer for ultrasound detection, which is only sensitive in its focal region, thus the lateral resolution and sensitivity drop dramatically when the targets move far from its focus. Even if a dynamic focusing algorithm is applied, the sensitivity out of the transducer focus is still much lower than that in the focus in ultrasonic imaging mode. In this work, we propose an acoustic-resolution PA/USE with a line-focused transducer to realize automatic focusing for the first time. In comparison to a point-focused transducer, the line-focused transducer emits a more uniform sound field, causing the original signal intensity and signal-to-noise ratio (SNR) of the front and rear targets to be closer in the radial direction, which is beneficial for improving target signal uniformity in ultrasonic imaging. Simultaneously, we improved the resolution of the defocus area by modifying a prior work of back-projection (BP) reconstruction algorithm typically used in point-focused transducer based PAE and applying it to line-focused PA/USE. This combined approach may significantly enhance the depth of field of ultrasonic imaging and the resolution of the defocus zone in PA/US imaging, compared to the conventional method. Sufficient numerical simulations and phantom experiments were performed to verify this method. The results show that our method can effectively improve the lateral resolution in the image’s defocused region to achieve automatic focusing and perfectly solve the defect of the target signal difference in the far-focus region in ultrasonic imaging, while also enhancing the image SNR and contrast. The proposed method in this paper lays foundations for the realization of photoacoustic/ultrasonic combined endoscopy with enhanced lateral resolution and depth of field, which can potentially benefit a many of biomedical applications.

Dual-Modality Imaging Microfluidic Cytometer for Onsite Detection of Phytoplankton

Phytoplankton monitoring is essential for better understanding and mitigation of phytoplankton bloom formation. We present a microfluidic cytometer with two imaging modalities for onsite detection and identification of phytoplankton: a lensless imaging mode for morphological features, and a fluorescence imaging mode for autofluorescence signal of phytoplankton. Both imaging modes are integrated in a microfluidic device with a field of view (FoV) of 3.7 mm × 2.4 mm and a depth of field (DoF) of 0.8 mm. The particles in the water flow channel can be detected and classified with automated image processing algorithms and machine learning models using their morphology and fluorescence features. The performance of the device was demonstrated by measuring Chlamydomonas, Euglena, and non-fluorescent beads in both separate and mixed flow samples. The recall rates for Chlamydomonas and Euglena ware 93.6% and 94.4%. The dual-modality imaging approach enabled observing both morphology and fluorescence features with a large DoF and FoV which contribute to high-throughput analysis. Moreover, this imaging flow cytometer platform is portable, low-cost, and shows potential in the onsite phytoplankton monitoring.

Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging

In synthetic aperture radar (SAR) imaging, geometric resolution, sidelobe level (SLL) and signal-to-noise ratio (SNR) are the most important parameters for measuring the SAR image quality. The staring spotlight mode continuously transmits signals to a fixed area by steering the azimuth beam to acquire azimuth high geometric resolution, and its two-dimensional (2D) impulse response with the low SLL is usually obtained from the 2D weighted power spectral density (PSD) by the selected weighting window function. However, this results in the SNR reduction due to 2D amplitude window weighting. In this paper, the staring spotlight SAR with nonlinear frequency modulation (NLFM) signal and azimuth non-uniform sampling (ANUS) is proposed to obtain high geometric resolution SAR images with the low SLL and almost without any SNR reduction. The NLFM signal obtains non-equal interval frequency sampling points under uniform time sampling by adjusting the instantaneous chirp rate. Its corresponding PSD is similar to the weighting window function, and its pulse compression result without amplitude window weighting has low sidelobes. To obtain a similar Doppler frequency distribution for low sidelobe imaging in azimuth, the received SAR echoes are designed to be non-uniformly sampled in azimuth, in which the sampling sequence is dense in middle and sparse in both ends, and azimuth compression result with window weighting would also have low sidelobes. According to the echo model of the proposed imaging mode, both the back projection algorithm (BPA) and range migration algorithm (RMA) are modified and presented to handle the raw data of the proposed imaging mode. Both imaging results on simulated targets and experimental real SAR data processing results of a ground-based radar validate the proposed low sidelobe imaging mode.

Evaluation of cytotoxicity and MRI contrast enhancement ability of Fe3O4@PLA-PEG iron oxide nanoparticles in vitro model

SPIONs are composed of Fe3O4 or gamma Fe2O3 cores and a biocompatible shell from Dextran, PLA, PEG, Chitosan, or PVA. SPIONs have many important applications in medicine and biology such as cell sorting, drug carrier, magnetic hyperthermia, and magnetic resonance imaging (MRI). This study aims to check the ability of copolymer PLA-PEG coated Fe3O4 ferromagnetic nanosystems (Fe3O4@PLA-PEG) produced for MRI application. The results showed that these nanoparticles had non-toxicity on BT-474 and Sarcoma 180 cell lines. Evaluation on T2 imaging mode revealed that Fe3O4@PLA-PEG nanoparticles were capable of enhancing the MRI image contrast in different conditions, including water, cell lysates solution, and even inside the cells. The report demonstrates that Fe3O4@PLA-PEG nanoparticles have a high potential application in MRI for clinical diagnosis.

Choroidal structural evaluation in celiac disease

This observational case–control study assessed the differences in choroidal structure between patients with celiac disease and healthy subjects utilizing the choroidal vascularity index (CVI). Seventy-four celiac patients and 67 healthy subjects underwent a complete ophthalmological evaluation, axial length (AL) measurements and spectral-domain optical coherence tomography with enhanced depth imaging mode (EDI SD-OCT) evaluation. These images were binarized and choroidal vasculature was analyzed. Choroidal total subfoveal area (TSA), luminal subfoveal area (LSA), stromal subfoveal area (SSA), CVI and subfoveal choroidal thickness (CT) were measured. Furthermore, subfoveal CT, TSA, LSA, SSA, and CVI were also correlated with AL. A statistically significant difference was found between the two groups for TSA, LSA, SSA and subfoveal CT, but not for CVI. In celiac patients, a significant correlation was found between AL and TSA, LSA and SSA, but not with CVI. Similar findings were also noticed in the healthy subjects. Thus, celiac patients have a thicker choroid than healthy subjects, regardless of the AL, due to a proportional increase in both the vascular and stromal components, which does not alter the CVI.

Biogenic Gas Vesicles for Ultrasound Imaging and Targeted Therapeutics

: Ultrasound is not only the most widely used medical imaging mode for diagnostics owing to its real-time, non-radiation, portable, and low-cost merits, but also a promising targeted drug/gene delivery technique by exhibiting a series of powerful bioeffects. The development of micron-sized or nanometer-sized ultrasound agents or delivery carriers further makes ultrasound a distinctive modality in accurate diagnosis and effective treatment. In this review, we introduce one kind of unique biogenic gas-filled protein nanostructures called gas vesicles, presenting some unique characteristics than the conventional microbubbles. Gas vesicles can not only serve as ultrasound contrast agents with innovative imaging methods such as cross-amplitude modulation harmonic imaging but also can further be adjusted and optimized via genetic engineering techniques. Moreover, they could not only serve as acoustic gene reporters, acoustic biosensors to monitor the cell metabolism, but also serve as cavitation nuclei and drug carriers for therapeutic purposes. In this study, we focus on the latest development and applications in the area of ultrasound imaging and targeted therapeutics, and also provide a brief introduction of the corresponding mechanisms. In summary, these biogenic gas vesicles show some advantages over conventional MBs that deserve more efforts to promote their development.