Journal of Biomedical Optics最新文献

Significance: Cervical cancer is the fourth most common cancer among women globally. Hence, it is crucial to develop a noninvasive and portable optical imaging modality for the early detection of premalignant cervical lesions.

Aim: We present the development and clinical validation of GynoSight v2.0, an indigenously developed multispectral, non-chip-on-tip source, hand-held, portable transvaginal imaging probe, for evaluating tissue health and identifying anomalies, such as those linked to precancerous cervical lesions.

Approach: GynoSight v2.0 houses a 16 LEDs, 5-megapixel camera, and a Raspberry Pi 5 module. A comparative shadowing effect analysis was performed between GynoSight v2.0 and colposcopy by evaluating statistical metrics such as mean pixel intensity (MPI), shadow area percentage (SAP), entropy, and contrast-to-noise ratio. In addition, the relative oxygen saturation maps of the cervical tissue were computed from the multispectral registered image using the proposed discrete Fourier transform-based image registration technique.

Results: The images of $N=6$ ( $N=2$ normal, $N=1$ premalignant, and $N=3$ high-grade squamous intraepithelial lesion) subjects were acquired. A comparative shadowing analysis shows a 50-unit gray level value separation between the colposcope and GynoSight v2.0 images. The pixel values of the colposcope are skewed to the lower pixel values, and the pixel values of GynoSight v2.0 are spread uniformly over 0 to 255 gray-level pixel values. In addition, the statistical analysis showed that MPI, SAP, and entropy are significant metrics for shadowing effect quantification.

Conclusions: The colposcopy images showed more shadowing effects than the GynoSight v2.0 images and hence provide better illumination to aid in better diagnosis.

Significance: The use of tissue attenuation coefficients as biomarkers for disease detection is rising. However, especially for ex vivo studies, sample handling methods can notably impact tissue optical attenuation properties, and these effects have yet to be studied in detail.

Aim: We aim to compare and evaluate common methods for sample handling and assess their impact on the optical attenuation and structural properties of ex vivo colon tissue.

Approach: Six different handling methods were tested: Direct freezing at $-80°C$ , slow freezing in a cryobox with and without cryopreservation media, snap freezing in isopentane, formalin fixation, and fresh tissue stored directly in phosphate-buffered saline. All samples were imaged using optical coherence tomography; images were assessed qualitatively for morphological changes and quantitatively by extracting the tissue attenuation coefficient using the Lambert-Beer law. All handling methods were compared with representative histology (hematoxylin and eosin staining and periodic acid-Schiff staining).

Results: All sample handling methods showed a significant difference in tissue attenuation and morphology relative to the fresh tissue ( $p\ll 0.0001$ ), with frozen samples generally showing a lower attenuation coefficient, e.g., directly frozen ( $2.0\pm 1.0{\mathrm{mm}}^{-1}$ ) compared with formalin-fixed ( $2.5\pm 1.3{\mathrm{mm}}^{-1}$ ) and fresh tissue ( $2.5\pm 1.0{\mathrm{mm}}^{-1}$ ). Formalin-fixed and snap frozen samples had the smallest effect size ( $\delta =0.002$ and $-0.09$ , respectively). Macroscopic structural changes were also observed, including alterations to the epithelial layer and indications of goblet cell degradation for all methods but formalin fixation.

Conclusions: Understanding the impact of sample handling methods is critical to the accurate interpretation of morphology-based analysis. In the case of fresh tissue being unavailable, formalin-fixed and snap frozen tissue samples yield the best alternative with negligible effect sizes for colon tissue.

Significance: Digital holographic microscopy (DHM) has proven effective for particle segmentation within a given volume, making it well-suited for rapid monitoring of bacterial growth in microfluidic cartridges-such as in single-cell-based antimicrobial susceptibility testing assays. However, the development of optimal assays depends on a range of factors related to the instrument, consumables, and the sample itself. Despite this, comprehensive investigations into how these parameters influence the quality of the resulting phase images remain limited.

Aim: To address this problem, we systematically explore the effect of these factors, including the microfluidic chamber height and its material properties, the density of the suspension, and other sample-inherent properties, on the signal-to-noise ratio (SNR) of the reconstructed phase image.

Approach: We constructed an off-axis digital holographic microscope and defined a robust numerical processing pipeline allowing for the numerical reconstruction, refocusing and counting of suspended particles in a measurement volume spanning roughly $120\times 120\times 400\mu m^3$ , at 50× magnification. We analyzed the performance of this system using various dilution steps of silica microspheres, Gram-positive spherical Staphylococcus warneri and Gram-negative rod-shaped Escherichia coli bacteria, filled in commercial microfluidic chips with different chamber heights.

Results: Experimental results demonstrated the system's capability in reflecting the dilution steps over 2 to 3 orders of magnitude. Our SNR analysis highlighted the microfluidic chamber height and the density of the suspension as key contributors to the background noise, whereas the particles themselves seemed to have a negligible effect. From this insight, we were able to derive an analytical function to predict the SNR of a given DHM system for various concentrations, chamber heights, and particle types.

Conclusions: We successfully built a DHM system for counting suspended particles over a wide concentration range and for various microfluidic chamber heights. We also derived an initial framework for predicting and optimizing the performance of a given DHM system.

Significance: Noninvasive monitoring of blood components is important in daily health management. Conventional optical techniques such as attenuated total reflection (ATR) have limited penetration depth and sensitivity. Photoacoustic spectroscopy using a piezoelectric transducer (PZT-PAS) can detect components in the interstitial fluid beneath the stratum corneum with a relatively simple device.

Aim: We explored the feasibility of PZT-PAS for noninvasive analysis of blood components.

Approach: Biomimetic phantom experiments were conducted to evaluate depth sensitivity. A technique for enhancing signal strength by generating standing acoustic waves in tissue was validated by tuning the laser modulation frequency. Human trials were conducted to assess the capability of the method for predicting blood glucose levels.

Results: PZT-PAS successfully detected signals from depths beyond 10 to $20\mu m$ , outperforming ATR. Signal enhancement was achieved in a 2-mm-thick interdigital membrane using resonant acoustic conditions. In human trials, discriminant analysis to determine blood glucose levels relative to a threshold of 140 mg/dL showed an accuracy rate of 85.3%.

Conclusions: These results highlight the potential of PZT-PAS combined with signal processing for future wearable, noninvasive health care monitoring applications.

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.