Journal of Biomedical Optics最新文献

Significance: Myocardial oxygen metabolism is a key focus of cardiac surgery. It serves as important evidence for surgeons to evaluate surgical quality and surgical plans. However, current clinical methods lack the capability to directly monitor dynamic changes in myocardial metabolism during surgery. Photoacoustic imaging (PAI), a biomedical optical imaging modality, offers real-time assessment of blood oxygen saturation. By visualizing oxygen saturation levels in both blood and muscle tissue, PAI provides a means to infer myocardial metabolic status intraoperatively.

Aim: We use PAI to observe the differences between infarcted myocardium and normal cardiac muscle and to explore the feasibility of using PAI to monitor myocardial metabolism levels during cardiac surgery.

Approach: Ten rabbits were randomly divided into experimental and control groups. The animals in the experimental group underwent thoracotomy followed by left anterior descending coronary artery ligation, whereas those in the control group received thoracotomy only. PAI was performed both at the beginning and before the end of the surgical procedure. The PAI results were compared between the two groups to analyze the relationship between myocardial PAI signal changes and oxygen metabolism levels.

Results: Following coronary ligation, the experimental group exhibited significant ST-segment elevation on electrocardiography, whereas no notable changes were observed in controls. PAI demonstrated: baseline myocardial oxygen saturation ( ${\mathrm{SmO}}_2$ ) ranged from 45% to 72% across all rabbits. Ligation-induced ischemia sharply reduced ${\mathrm{SmO}}_2$ to 1% to 19% in experimental animals. Control animals maintained stable ${\mathrm{SmO}}_2$ levels throughout the procedure. Histopathological examination confirmed extensive myocardial necrosis in the apical region of ligated rabbits, consistent with the observed functional and metabolic alterations.

Conclusions: PAI can detect myocardial oxygen saturation in real-time during surgery and determine the occurrence of myocardial ischemia and changes in oxygen metabolism levels based on differences in oxygen saturation.

Significance: Fast, high-throughput fluorescence imaging is essential for numerous biomedical applications, particularly in high-resolution volumetric tissue analysis.

Aim: We aim to develop an imaging strategy that combines the strengths of multiplane microscopy and extended depth-of-field (EDOF) microscopy and to characterize its performance on tissue samples.

Approach: We employed 2.5D microscopy, an EDOF approach optimized for high-resolution imaging, and integrated it with a quad-plane image splitter. This technique enables simultaneous capture of four focal volumes using a single camera, allowing volumetric imaging of $\sim 16$ to $20\mu m$ thick mouse and human tissues prepared as frozen or formalin-fixed, paraffin-embedded sections.

Results: Our approach achieves a 25-fold reduction in image acquisition time compared with conventional $z$ -scanning widefield microscopy. For example, a $2mm\times 2mm\times 16\mu m$ volume can be imaged in 4.7 min, down from $\sim 2h$ . We further demonstrate compatibility with multicolor imaging and successful application to nucleus segmentation for downstream analysis.

Conclusions: This imaging technique provides a promising tool for tissue analysis, offering significant improvements in volumetric imaging speed with minimal compromise in spatial resolution and sensitivity.

Significance: There is an unmet need for readily accessible imaging targets to verify whether devices can discriminate lesions from healthy tissue and identify sub-surface vasculature in the small airways.

Aim: Our aim is to develop a phantom that mimics human segmental airway adenocarcinoma in vivo for 1310 nm endoscopic optical coherence tomography (OCT) and angiography characterization.

Approach: We develop phantoms using a mixture of agar, intralipid, and coconut oil cured in a 3D printed mold with embedded tubing to mimic vasculature. The parenchyma optical attenuation coefficient (OAC) is calibrated using optical transmission measurements from an agar and intralipid dilution series. Depth-resolved OAC histogram distributions, analysis of variance, and image quality are used to assess repeatability and biofidelity of these phantoms.

Results: Transmission measurements show large increases in OAC when intralipid is cured with agar compared with water-intralipid dilutions. Representative phantom OACs show repeatability within 2.7% and match normal in vivo tissue measurements within 16%. Embedded lesion phantoms achieve imaging characteristics of in vivo adenocarcinoma. Fluid flow within embedded tubing is visualized with Doppler OCT.

Conclusions: The segmental airway phantoms demonstrate in vivo human imaging characteristics, including structural and optical markers of pathological progression-providing a platform for imaging system characterization and optimization.

Significance: Interproximal caries detection is critical for effective dental treatment. We report an ultrathin lensed fiber-based manual scanning optical coherence tomography (OCT) needle probe to enables the direct imaging of the interproximal caries between two adjacent teeth.

Aim: We aim to design and fabricate the ultrathin lensed fiber-based manual scanning OCT needle probe, and validate the performance of the proposed probe by applying it to the imaging of the phantom sample, the human skin tissue and the interproximal caries between two adjacent teeth.

Approach: A homemade lensed fiber is packaged into a 21-gauge hypodermic needle to create a high-flexibility, ultrathin probe. A decorrelation algorithm is employed for image reconstruction based on manual scanning. The performances of the developed needle probe are experimentally measured. The probe is incorporated in a swept-source OCT system to image the phantom sample, the human skin tissue, and the interproximal caries between two adjacent teeth.

Results: The working distance and focused spot diameter of the developed probe are measured to be 1.22 mm and $18.78\mu m$ , respectively. The correctly reconstructed OCT images of the phantom, skin tissue, and the tooth tissue demonstrate the performance of the developed ultrathin lensed fiber-based manual scanning OCT needle probe. The distinct structural difference between the healthy and abnormal teeth tissue validates the efficacy of the proposed method.

Conclusion: We propose an ultrathin lensed fiber-based manual scanning OCT needle probe potentially useful for the interproximal caries detection. The design, fabrication, and performances of the developed needle probe are demonstrated. We address a critical issue in the caries diagnostics and offer a promising tool for the future clinical applications.

Significance: Multi-exposure speckle imaging (MESI) is a label-free technique to visualize and measure blood flow. Accurate perfusion measurements are useful in a variety of applications, including surgery, monitoring treatment, and diagnosing various conditions.

Aim: We aim to demonstrate the feasibility of capturing speckle images through an optical fiber bundle for use in MESI for potential applications such as endoscopy or where free space measurements are not feasible.

Approach: To compare the accuracy of fiber bundle MESI measurements against free space MESI measurements, measurements of a tissue-simulating flow phantom and in vivo mouse cortex were acquired simultaneously through free space and an optical fiber bundle.

Results: Using the Pearson correlation coefficient for comparing measurements, $R^2$ values of 0.9994 and 0.9942 were calculated for low (1 to $10\mu L/\min$ ) and high (10 to $100\mu L/\min$ ) flow rates, respectively. For in vivo measurements, an $R^2$ value of 0.970 was calculated for flow in 14 vessels and 5 parenchyma regions. $R^2$ values of 0.953 and 0.906 were calculated for two vessels before, during, and after a stroke.

Conclusions: MESI measurements through an optical fiber bundle show similar results to free-space MESI.

Significance: Continuous and longitudinal monitoring of cerebral blood flow (CBF) is critical for understanding brain pathophysiology and guiding interventions. Although rodents are the primary models in neuroscience, existing imaging modalities often fail to provide the optimal combination of low cost, high spatiotemporal resolution, wide head coverage, and sufficient penetration depth for small-animal brain imaging.

Aim: Leveraging a clinical speckle contrast diffuse correlation tomography (scDCT) system, we aimed to develop an affordable, user-friendly, fast, and miniaturized scDCT (mini-scDCT) device tailored for depth-sensitive CBF imaging in small rodents.

Approach: The mini-scDCT replaces bulky and costly optoelectronic components with compact, low-cost alternatives while preserving imaging performance. It is mounted on a standard stereotaxic apparatus for portability and ease of use. Temporal resolution was improved by hardware synchronization and software optimization. System validation was performed using head-simulating phantoms and rodent models under various pathophysiological conditions.

Results: Compared with the original scDCT, the mini-scDCT achieved a fourfold cost reduction, a fivefold footprint reduction, and eightfold improvement in temporal resolution per source. Validation experiments confirmed the system's depth sensitivity in head-simulating phantoms and its ability to detect both global and regional CBF changes in rodents, with results consistent with physiological expectations and prior studies.

Conclusion: The mini-scDCT offers an affordable, user-friendly, depth-sensitive platform for functional brain imaging in rodent models. Its reduced cost and compact footprint enhance accessibility, whereas the improved spatiotemporal resolution enables diverse applications such as imaging brain functional connectivity in neuroscience research.

Significance: Single-chip multispectral imaging sensors with vertically stacked photodiodes and pixelated spectral filters enable advanced, real-time visualization for image-guided cancer surgery. However, their design inherently reduces spatial resolution. We present a convolutional neural network (CNN)-transformer demosaicing algorithm, validated on both clinical and preclinical datasets that effectively doubles spatial resolution and improves image quality-substantially enhancing intraoperative cancer visualization.

Aim: We present a CNN-transformer-based demosaicing approach specifically optimized for reconstructing high-resolution color and NIR images acquired by a hexachromatic imaging sensor.

Approach: A hybrid CNN-transformer demosaicing model was developed and trained on color-image datasets, then rigorously evaluated on color and NIR images to demonstrate superior reconstruction quality compared with conventional bilinear interpolation and residual CNN methods.

Results: Our CNN-transformer demosaicing method achieves an average mean squared error (MSE) reduction of $\sim 85\%$ for color images and 76% for NIR images and improves structural dissimilarity by roughly 72% and 79%, respectively, compared with state-of-the-art CNN-based demosaicing algorithms in preclinical datasets. In clinical datasets, our approach similarly demonstrates significant reductions in MSE and structural dissimilarity, substantially outperforming existing CNN-based methods, particularly in reconstructing high-frequency image details.

Conclusions: We demonstrate improvements in spatial resolution and image fidelity for color and NIR images obtained from hexachromatic imaging sensors, achieved by integrating convolutional neural networks with transformer architectures. Given recent advances in GPU computing, our CNN-transformer approach offers a practical, real-time solution for enhanced multispectral imaging during cancer surgery.

Significance: Leukemia, a complex hematological cancer, poses significant diagnostic challenges due to the heterogeneity of leukemic cells, inter-observer variability, and lack of standardized analysis methodology. Accurate and rapid cell classification is essential to improve clinical management, optimize treatment, and reduce diagnostic errors.

Aim: We propose an innovative approach combining optical scanning holography (OSH) and active contour (AC) models to automate the classification and segmentation of leukemic cells with increased accuracy.

Approach: OSH is used to capture the phase current of leukocytes, providing a cost-effective, noninvasive, and simplified alternative to conventional techniques. AC models are used to improve cell segmentation. Analysis of the maximum amplitude values of the phase current allows rapid and fully automated classification.

Results: The proposed approach shows a significant improvement in terms of reliability, speed, and reproducibility compared with existing methods. The integration of OSH and AC enables robust segmentation and efficient classification of leukemic cells.

Conclusion: This method provides a reliable, rapid, and systematic solution for the accurate diagnosis of leukemia, enabling optimized therapeutic management.

Significance: Accurate cell classification is essential in disease diagnosis and drug screening. Three-dimensional (3D) voxel models derived from holographic tomography effectively capture the internal structural features of cells, enhancing classification accuracy. However, their high dimensionality leads to significant increases in data volume, computational complexity, processing time, and hardware costs, which limit their practical applicability.

Aim: We aim to develop an efficient and accurate cell classification method using 3D refractive index (RI) point cloud data obtained from holographic tomography, focusing on reducing computational complexity without sacrificing classification performance.

Approach: We transformed 3D RI voxel data into point cloud representations using segmented equilibrium sampling to substantially decrease data volume while retaining crucial structural features. A deep learning model, named RI-PointNet++, was then specifically designed for RI point cloud data to enhance feature extraction and enable precise cell classification.

Results: In experiments classifying the viability of HeLa cells, the proposed method achieved a classification accuracy of 93.5%, significantly outperforming conventional two-dimensional models (87.0%). Furthermore, compared with traditional 3D voxel-based models, our method reduced computational complexity by over 99%, with floating-point operations of only 1.49 G, thus enabling efficient performance even on central processing unit (CPU) hardware.

Conclusions: Our proposed method provides an innovative, lightweight solution for 3D cell classification, highlighting the considerable potential of point cloud-based approaches in biomedical research applications.

Significance: Near-infrared spectroscopy (NIRS) imaging modalities are used to provide noncontact measurements of tissue oxygenation in diabetic foot ulcers. However, the curved surface of the diabetic foot introduces inaccurate tissue oxygenation measurement. The changes in spatial NIRS optical measurements may result from variations in the underlying physiology or from the curvature of the tissue surface. Therefore, the effect of tissue curvature must be accounted for to ensure the accurate measurement of tissue oxygenation (or hemoglobin parameters) in clinical applications.

Aim: Our aim is to develop and validate mathematical curvature correction models to account for the effects of tissue curvature on diffuse reflectance (DR) in NIRS imaging and assess their effect on the hemoglobin parameters as well.

Approach: Monte-Carlo-based light propagation simulations were performed to develop correction models and applied to three-layered curved geometries in MCMatlab. Four curvature correction models based on height and/or angle were developed via Monte Carlo simulation studies. All the correction models were applied to the simulated DR signals obtained from various curved geometries (concave, convex, and wound-mimicking) using Gaussian light sources at 690 and 830 nm. The effect of correction models on DR signals and hemoglobin parameters was determined.

Results: Simulation results showed that a concave curved surface did not require correction, whereas convex and wound-mimicking geometries showed a reduced median error upon using an empirical height/angle correction model. In addition, the correction model also reduced the median error significantly for the oxygen-saturation-based hemoglobin parameter in both the convex and wound-mimicking geometries.

Conclusions: The developed mathematical model effectively corrected tissue curvature effects in NIRS DR signals and hemoglobin parameters for wound-mimicking irregular geometry. Ongoing work focuses on experimental validation of these correction models on curved phantoms, prior to in vivo imaging studies.