Long-term Radiological and Pulmonary Function Abnormalities at 3-year post COVID-19 Hospitalization: A Longitudinal Cohort Study.

BACKGROUND: This study aimed to evaluate the longitudinal progression of residual lung abnormalities (ground-glass opacities, reticulations, and fibrotic-like changes) and pulmonary function, three years following coronavirus disease 2019(COVID-19). METHODS: This prospective, longitudinal cohort study enrolled COVID-19 survivors who exhibited residual lung abnormalities upon discharge from two hospitals. Follow-up assessments were conducted at 6 months, 12 months, 2 years, and 3 years post-discharge, and included pulmonary function tests, 6-minute walk distance (6MWD), chest CT scans, and symptom questionnaires. Non-COVID-19 controls were retrospectively recruited for comparative analysis. RESULTS: 728 COVID-19 survivors and 792 controls were included. From 6 months to 3 years, there was a gradual improvement in reduced diffusing capacity of the lungs for carbon monoxide (DLCO＜80% predicted, 49% versus 38%, p=0.001), 6MWD (496 m versus 510 m, p=0.002) and residual lung abnormalities(46% versus 36%, p<0.001), regardless of the disease severity. Patients with residual lung abnormalities at 3 years more commonly had respiratory symptoms (32% versus 16%, p<0.001), lower 6MWD (494 m versus 510 m, p=0.003), and abnormal DLCO (57% versus 27%, p<0.001) compared to those with complete resolution. Compared to the controls, the proportion of DLCO impairment (38% versus 17%, p<0.001) and respiratory symptoms (23% versus 2.2%, p<0.001) were significantly higher in the matched COVID-19 survivors at the 3-year follow-up. CONCLUSIONS: Most patients exhibited improvement in radiological abnormalities and pulmonary function over time following COVID-19. However, more than one-third continued to have persistent lung abnormalities at the 3-year mark, which were associated with respiratory symptoms and reduced diffusion capacity.

Risk factors for distal stent graft-induced new entry after endovascular repair in uncomplicated type B aortic dissection.

OBJECTIVE: We investigated the risk factors for distal stent graft-induced new entry (dSINE) after thoracic endovascular aortic repair for patients with uncomplicated type B aortic dissection (TBAD) and reported the outcomes of using a tapered stent graft and dSINE reintervention. METHODS: A total of 226 patients with uncomplicated TBAD who had undergone thoracic endovascular aortic repair between January 2010 and December 2018 were analyzed retrospectively. The global features of the thoracic aorta and the local features of the proximal and distal landing zones were evaluated and compared between the dSINE and non-dSINE groups. A multivariate Cox model was used to identify the independent risk factors for dSINE. The cumulative incidence of reintervention was estimated using competing risk models. RESULTS: After a median follow-up of 4.6 years, 16 patients (7.1%) had developed dSINE. Multivariable Cox regression analysis demonstrated that a type III aortic arch, decreased angle, increased distal oversizing, and increased distal mismatch ratio were significant risk factors for dSINE. Of the patients with tapered stent grafts, five with a ≤4-mm taper had developed dSINE. However, no dSINE was seen in the >4-mm taper group (P = .024). Reintervention was performed for 7 of the 16 patients with dSINE (43.8%). The mean time from the initial detection of dSINE to reintervention was 6.43 ± 4.62 months. The competing risk analyses showed that the cumulative incidence of reintervention in the dSINE group at 1, 3, and 5 years was 25.0%, 37.5%, and 43.5%, respectively. CONCLUSIONS: A type III aortic arch, excessive distal oversizing and mismatch ratio, and severe angulation were associated with dSINE in patients with uncomplicated TBAD. The use of a tapered stent graft with a >4-mm taper could help prevent dSINE in patients with a high taper ratio. Aggressive reintervention was associated with favorable long-term outcomes for patients with progressive dSINE.

The Impact of Oversizing in Thoracic Endovascular Aortic Repair on Long-Term Outcomes in Uncomplicated Type B Aortic Dissection: A Single-Center Retrospective Study.

PURPOSE: The purpose of this study was to assess the impact of oversizing in thoracic endovascular aortic repair (TEVAR) on early and long-term survival and major adverse events in patients with uncomplicated type B aortic dissection (TBAD). METHODS: Between January 2010 and December 2018, 226 patients who were diagnosed with uncomplicated TBAD and received TEVAR were analyzed retrospectively. The patients were divided into ≤5% oversizing (n=153) and >5% oversizing (n=73) groups. Primary end points were all-cause and aortic-related mortalities. Secondary end points were procedure-related complications, including retrograde type A aortic dissection (RTAD), endoleak, distal stent-induced new entry (SINE), and late reintervention. All-cause and aortic-related mortalities were assessed using the Kaplan-Meier survival method, while procedure-related complications were evaluated using a competing risk model with all-cause death as a competing risk. RESULTS: Mean oversizing was 2.1%±1.5% in the ≤5% oversizing group and 9.6%±4.1% in the >5% oversizing group. Differences in the 30-day mortality and adverse events between the 2 groups were statistically insignificant. The freedom from all-cause mortality was comparable between the ≤5% oversizing group and the >5% oversizing group (≤5%: 93.3% at 5 years, >5%: 92.3% at 5 years, p=0.957). No significant difference was observed between both groups in the freedom from aortic-related mortality (≤5%: 95.0% at 5 years, >5%: 96.7% at 5 years, p=0.928). However, the competing risk analyses revealed that the cumulative incidence of RTAD was statistically significantly greater in the >5% oversizing group than in the ≤5% oversizing group (≤5%: 1(0.7%) at 5 years, >5%: 6(6.9%) at 5 years, p=0.007). All RTADs occurred within a year of TEVAR. The differences in the cumulative incidences of type I endoleak, distal SINE, and late reintervention were not significant between the 2 groups. CONCLUSION: The differences in the 5-year all-cause mortality and aortic-related mortality between patients with uncomplicated TBAD who received TEVAR with ≤5% oversizing and those who got TEVAR with >5% oversizing were insignificant. However, oversizing >5% was considerably associated with an increased risk of RTAD within a year of TEVAR, suggesting that oversizing ≤5% may be the appropriate size for TEVAR in patients with uncomplicated TBAD. CLINICAL IMPACT: For patients with uncomplicated TBAD, choosing oversizing ≤5% in endovascular treatment is beneficial to reduce the risk of postoperative retrograde type A aortic dissection. This finding provides a basis for stent size selection in endovascular repair. In addition, one year after TEVAR is the main time period for postoperative retrograde type A aortic dissection, and attention should be paid to the management and follow-up of this period.

Efficacy, mechanism, and safety of melatonin-loaded on thermosensitive nanogels for rabbit VX2 tumor embolization: A novel design.

Transarterial chemoembolization (TACE) has been widely used for hepatocellular carcinoma. Reducing hypoxia in the tumor microenvironment after TACE remains a challenge as tumor progression is common in post-TACE patients due to the hypoxic tumor microenvironment. In this study, melatonin loaded on p(N-isopropyl-acrylamide-co-butyl methylacrylate) (PIB-M) was used for tumor embolism. Two types of human hepatoma cell lines were used to explore the mechanism by which melatonin prevents the growth and metastasis of cancer cells in vitro. A VX2 rabbit tumor model was used to evaluate the efficacy, mechanism, and safety of PIB-M in vivo. We found that under hypoxic condition, melatonin could inhibit tumor cell proliferation and migration by targeting hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor A (VEGF-A) in vitro. In vivo, PIB-M inhibited tumor growth and metastasis in rabbit VX2 tumors by promoting apoptosis of tumor cells and targeting related angiogenic proteins and vascular permeability proteins. A high concentration of melatonin in the PIB-M group could be maintained in tumor tissue for 72 h after embolization. The liver and kidney functions were most damaged on the first day but recovered to normal on the seventh day after embolization in the PIB-M group. This novel method may open avenues for reduction of tumor growth and metastasis after TACE and is efficacy and safety, which may be used for treatment for other solid tumors and clinical translation.

Multiscale high-speed photoacoustic microscopy based on free-space light transmission and a MEMS scanning mirror.

The conventional photoacoustic microscopy (PAM) system allows trade-offs between lateral resolution and imaging depth, limiting its applications in biological imaging in vivo. Here we present an integrated optical-resolution (OR) and acoustic-resolution (AR) multiscale PAM based on free-space light transmission and fast microelectromechanical systems (MEMS) scanning. The lateral resolution for OR is 4.9 µm, and the lateral resolution for AR is 114.5 µm. The maximum imaging depth for OR is 0.7 mm, and the maximum imaging depth for AR is 4.1 mm. The imaging speed can reach 50 k Alines per second. The high signal-to-noise ratios and wavelength throughput are achieved by delivering light via free-space, and the high speed is achieved by a MEMS scanning mirror. The blood vasculature from superficial skin to the deep tissue of a mouse leg was imaged in vivo using two different resolutions to demonstrate the multiscale imaging capability.

Effect of metformin on hepatocellular carcinoma patients with type II diabetes receiving transarterial chemoembolization: a multicenter retrospective cohort study.

BACKGROUND: Diabetes is prevalent among patients with hepatocellular carcinoma (HCC) and is associated with a poor prognosis. Although the hypoglycemic drug metformin has shown anti-tumor effects, its potential positive effect on patients with HCC and diabetes undergoing transarterial chemoembolization (TACE) remains unclear. Therefore, this study aimed to investigate the efficacy and safety of metformin in patients with HCC and type II diabetes who are receiving TACE. MATERIALS AND METHODS: This retrospective study involved 372 consecutive patients with HCC and type II diabetes across three medical centers between January 2014 and June 2021. All patients underwent TACE. Propensity score matching (PSM) was used to reduce selection bias. Cox proportional hazards regression was employed to compare all-cause death between the metformin and non-metformin groups, while competing risk regression was performed to assess cancer-specific death. RESULTS: Among 372 patients included in the study, 208 patients (177 male patients and 31 female patients) with mean age 59.6 (10.3) years received metformin and 164 patients (139 male patients and 25 female patients) with mean age 60.3 (10.0) years did not. Before PSM, patients with metformin had significantly longer median overall survival (mOS) and median progression-free survival (mPFS) than those without metformin (mOS: 34 months, 95% CI: 25.6-42.4 vs. 20 months, 95% CI: 15.3-24.7; P<0.001; mPFS: 11 months, 95% CI: 9.3-12.7 vs. 8 months, 95% CI: 5.9-10.1; P<0.001). Similar results were observed after PSM. Multivariate regression analysis indicated that metformin was associated with a reduced risk of all-cause mortality (HR: 0.589, 95% CI: 0.454-0.763; P<0.001) and tumor progression (HR: 0.667, 95% CI: 0.526-0.845; P=0.001) before PSM. After excluding deaths related to other factors, metformin continued to demonstrate a reduction in cancer-specific mortality risk among the patients. Subgroup analysis further revealed that patients using metformin had lower all-cause mortality risk and tumor progression risk than those without metformin in most subgroups. Adverse event evaluation suggested that metformin could lead to elevated nausea incidence. CONCLUSION: Metformin may confer survival benefits to patients with HCC and type II diabetes undergoing TACE. Metformin may simultaneously address multiple aspects of treatment in these patients.

Recent advances in oncolytic virus therapy for hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a highly refractory cancer and the fourth leading cause of cancer-related mortality worldwide. Despite the development of a detailed treatment strategy for HCC, the survival rate remains unsatisfactory. Oncolytic virus has been extensively researched as a new cancer therapeutic agent in the treatment of HCC. Researchers have designed a variety of recombinant viruses based on natural oncolytic diseases, which can increase the targeting of oncolytic viruses to HCC and their survival in tumors, as well as kill tumor cells and inhibit the growth of HCC through a variety of mechanisms. The overall efficacy of oncolytic virus therapy is known to be influenced by anti-tumor immunity, toxic killing effect and inhibition of tumor angiogenesis, etc. Therefore, a comprehensive review of the multiple oncolytic mechanisms of oncolytic viruses in HCC has been conducted. So far, a large number of relevant clinical trials are under way or have been completed, and some encouraging results have been obtained. Studies have shown that oncolytic virus combined with other HCC therapies may be a feasible method, including local therapy, chemotherapy, molecular targeted therapy and immunotherapy. In addition, different delivery routes for oncolytic viruses have been studied so far. These studies make oncolytic virus a new and attractive drug for the treatment of HCC.

ADSeg: A flap-attention-based deep learning approach for aortic dissection segmentation.

Accurate and rapid segmentation of the lumen in an aortic dissection (AD) is an important prerequisite for risk evaluation and medical planning for patients with this serious condition. Although some recent studies have pioneered technical advances for the challenging AD segmentation task, they generally neglect the intimal flap structure that separates the true and false lumens. Identification and segmentation of the intimal flap may simplify AD segmentation, and the incorporation of long-distance z axis information interaction along the curved aorta may improve segmentation accuracy. This study proposes a flap attention module that focuses on key flap voxels and performs operations with long-distance attention. In addition, a pragmatic cascaded network structure with feature reuse and a two-step training strategy are presented to fully exploit network representation power. The proposed ADSeg method was evaluated on a multicenter dataset of 108 cases, with or without thrombus; ADSeg outperformed previous state-of-the-art methods by a significant margin and was robust against center variation.

Effect of Transarterial Chemoembolization Plus Percutaneous Ethanol Injection or Radiofrequency Ablation for Liver Tumors.

Background: The efficacy of the transarterial chemoembolization (TACE) process combined with percutaneous ethanol injection (PEI, TACE-P) or the radiofrequency ablation (RFA, TACE-R) process was found to be good when used for the treatment of patients suffering from early or intermediate hepatocellular carcinoma (eiHCC). The study was conducted to compare the efficacy and safety of the TACE-P with TACE-A processes followed during the treatment of patients with eiHCC. Methods: A total of 241 patients suffering from eiHCC, subjected to TACE-P (147 patients) or TACE-R (94 patients) processes from January 1, 2014, to December 31, 2018, were retrospectively reviewed and included. The propensity score matching (PSM) method was used to reduce selection bias. Results: The median overall survival (mOS) and progression-free survival (mPFS) of the TACE-P group were similar to those recorded for the TACE-R group (P>0.05) before using the PSM technique. Similar results were obtained post the use of the PSM technique. In the subgroup analysis after PSM, patients with single tumor (dimension: ≤5 cm), who were subjected to TACE-P-based treatment methods, exhibited worse tumor response than patients subjected to TACE-R-based methods (HR: 1.804, 95% CI: 1.083-3.005, P=0.023). Seven adverse events were reported. A statistically significant difference for all grades of adverse events (and grade III or IV adverse events) between the two groups (all P>0.05) was not reported. Conclusion: The benefits and advantages of using the TACE-P based method was similar was those obtained using the TACE-R in patients with eiHCC, especially for patients with a single large tumor or multiple tumors.

Self-supervised learning enables 3D digital subtraction angiography reconstruction from ultra-sparse 2D projection views: A multicenter study.

3D digital subtraction angiography (DSA) reconstruction from rotational 2D projection X-ray angiography is an important basis for diagnosis and treatment of intracranial aneurysms (IAs). The gold standard requires approximately 133 different projection views for 3D reconstruction. A method to significantly reduce the radiation dosage while ensuring the reconstruction quality is yet to be developed. We propose a self-supervised learning method to realize 3D-DSA reconstruction using ultra-sparse 2D projections. 202 cases (100 from one hospital for training and testing, 102 from two other hospitals for external validation) suspected to be suffering from IAs were conducted to analyze the reconstructed images. Two radiologists scored the reconstructed images from internal and external datasets using eight projections and identified all 82 lesions with high diagnostic confidence. The radiation dosages are approximately 1/16.7 compared with the gold standard method. Our proposed method can help develop a revolutionary 3D-DSA reconstruction method for use in clinic.

The Effect of Alcohol Consumption in Unresectable Hepatocellular Carcinoma with Transarterial Chemoembolization.

Background: Alcohol consumption can increase the risk of developing hepatocellular carcinoma (HCC). However, whether continuous alcohol consumption can influence outcomes in patients with HCC who undergo transarterial chemoembolization (TACE) remains unclear. This study aimed to explore the effect of alcohol consumption in patients with unresectable HCC who underwent TACE. Methods: The data used in the study were obtained from two centers and were retrospectively reviewed between January, 2014, and December, 2021. 254 patients with TACE were included in this study. Among them, 101 patients were continuous alcohol consumers and 153 patients had alcohol abstinence. Propensity score matching (PSM) and competing risk analysis were used to reduce the selection bias. Results: The median overall survival (mOS) and median progression-free survival (mPFS) in the alcohol consumers' group were longer than those in the alcohol abstinence group, before and after PSM. Multivariate regression analysis showed that alcohol consumption increased all-cause mortality risk (HR: 1.486, 95% CI: 1.074-2.055; P=0.016) and tumor progression risk (HR: 1.434, 95% CI: 1.091-1.886; P=0.01) more than that with alcohol abstinence. In the competing risk analysis, after excluding deaths caused by other reasons, alcohol consumption increased cancer-specific mortality risk more than alcohol abstinence did before and after PSM. Adverse event analysis showed that alcohol consumption increased the risk of all grades of nausea and vomiting and grade III or IV nausea more than alcohol abstinence did after patients underwent TACE. Conclusion: Alcohol consumption may lead to a poor prognosis and increase adverse events in patients receiving TACE compared to those with alcohol abstinence.

Deep Learning Enables Superior Photoacoustic Imaging at Ultralow Laser Dosages.

Optical-resolution photoacoustic microscopy (OR-PAM) is an excellent modality for in vivo biomedical imaging as it noninvasively provides high-resolution morphologic and functional information without the need for exogenous contrast agents. However, the high excitation laser dosage, limited imaging speed, and imperfect image quality still hinder the use of OR-PAM in clinical applications. The laser dosage, imaging speed, and image quality are mutually restrained by each other, and thus far, no methods have been proposed to resolve this challenge. Here, a deep learning method called the multitask residual dense network is proposed to overcome this challenge. This method utilizes an innovative strategy of integrating multisupervised learning, dual-channel sample collection, and a reasonable weight distribution. The proposed deep learning method is combined with an application-targeted modified OR-PAM system. Superior images under ultralow laser dosage (32-fold reduced dosage) are obtained for the first time in this study. Using this new technique, a high-quality, high-speed OR-PAM system that meets clinical requirements is now conceivable.

Full three-dimensional segmentation and quantification of tumor vessels for photoacoustic images.

Quantitative analysis of tumor vessels is of great significance for tumor staging and diagnosis. Photoacoustic imaging (PAI) has been proven to be an effective way to visualize comprehensive tumor vascular networks in three-dimensional (3D) volume, while previous studies only quantified the vessels projected in one plane. In this study, tumor vessels were segmented and quantified in a full 3D framework. It had been verified in the phantom experiments that the 3D quantification results have better accuracy than 2D. Furthermore, in vivo vessel images were quantified by 2D and 3D quantification methods respectively. And the difference between these two results is significant. In this study, complete vessel segmentation and quantification method within a 3D framework was implemented, which showed obvious advantage in the analysis accuracy of 3D photoacoustic images, and potentially improve tumor study and diagnosis.

A new deep learning method for image deblurring in optical microscopic systems.

Deconvolution is the most commonly used image processing method in optical imaging systems to remove the blur caused by the point-spread function (PSF). While this method has been successful in deblurring, it suffers from several disadvantages, such as slow processing time due to multiple iterations required to deblur and suboptimal in cases where the experimental operator chosen to represent PSF is not optimal. In this paper, we present a deep-learning-based deblurring method that is fast and applicable to optical microscopic imaging systems. We tested the robustness of proposed deblurring method on the publicly available data, simulated data and experimental data (including 2D optical microscopic data and 3D photoacoustic microscopic data), which all showed much improved deblurred results compared to deconvolution. We compared our results against several existing deconvolution methods. Our results are better than conventional techniques and do not require multiple iterations or pre-determined experimental operator. Our method has several advantages including simple operation, short time to compute, good deblur results and wide application in all types of optical microscopic imaging systems. The deep learning approach opens up a new path for deblurring and can be applied in various biomedical imaging fields.

De-noising of photoacoustic sensing and imaging based on combined empirical mode decomposition and independent component analysis.

Photoacoustic (PA) imaging breaks the diffusion limit of conventional optical imaging by listening to the PA wave. As a new kind of functional imaging method, it has experienced tremendous growth in research community with wide range of applications. However, it is still an open and fundamental challenge that the conversion efficiency from light to sound based on PA effect is extremely low. The consequence is the poor signal-to-noise ratio (SNR) of PA signal especially in scenarios of low laser power and deep penetration. Conventional approach to enhance the SNR of PA signal in these noisy scenarios is data averaging, which is quite time-consuming. To improve the signal fidelity and imaging speed, an algorithm of using empirical mode decomposition and independent component analysis de-noising methods in PA imaging is proposed. The simulation and in vivo experimental results show obvious SNR enhancement of the PA signal and image contrast. The proposed method provides the potential to develop real-time low-cost PA imaging system with low-power laser source.

Optical-resolution photoacoustic microscopy for monitoring vascular normalization during anti-angiogenic therapy.

Monitoring the changes in tumor vascularity is important for anti-angiogenic therapy assessment with therapeutic implications. However, monitoring vascularity is quite challenging due to the lack of appropriate imaging techniques. Here, we describe a non-invasive imaging technique using optical-resolution photoacoustic microscopy (OR-PAM) to track vascular changes in prostate cancer treated with an anti-angiogenic agent, DC101, on a mouse ear xenograft model. Approximately 1-3 days after the initial therapy, OR-PAM imaging detected tumor vascular changes such as reduced vessel tortuosity, decreased vessel diameter and homogenized intratumoral vessel distribution. These observations indicated vessel normalization, which was pathologically validated as increased fractional pericyte coverage, functional perfusion and drug delivery of the vessels. After four DC101 interventions, OR-PAM imaging eventually revealed intratumoral vessel regression. Therefore, OR-PAM imaging of the vasculature offers a promising method to study anti-angiogenic drug mechanisms of action in vivo and holds potential in monitoring and guiding anti-angiogenic therapy.

Lack of association between acupoint sensitization and microcirculatory structural changes in a mouse model of knee osteoarthritis: A pilot study.

As a stimulating point in acupuncture, acupoint has unique microcirculatory features, and its dynamics vary greatly depending on health status. Acupoint sensitization is defined as the transformation of an acupoint from a "silenced status" (healthy) to an "activated status" (disease). Our previous study demonstrated that acupoint sensitization is associated with an increase in the level of local blood perfusion. However, the structural changes in microcirculation during acupoint sensitization have yet to be elucidated because the high-resolution microcirculation imaging of acupoints has been difficult to obtain. In this study, the structural changes in microcirculation at the Zusanli (ST36), Yanglingquan (GB34) and nonacupoint sites on days 0, 7 and 21 were dynamically observed during acupoint sensitization in an experimental knee osteoarthritis mouse model by using optical-resolution photoacoustic microscopy. The results showed that no significant differences in microvessel density, the distribution of vessel diameters or vascular tortuosity were observed at the GB34, ST36 or nonacupoint sites among days 0, 7 and 21. We proposed that acupoint sensitization may not be associated with the structural changes in microcirculation and that the microcirculatory changes during acupoint sensitization are more likely to be functional. The functional characteristics of the sensitized acupoints warrant further investigation.

Motion Correction in Optical Resolution Photoacoustic Microscopy.

In this paper, we are proposing a novel motion correction algorithm for high-resolution OR-PAM imaging. Our algorithm combines a modified demons-based tracking approach with a newly developed multi-scale vascular feature matching method to track motion between adjacent B-scan images without needing any reference object. We first applied this algorithm to correct motion artifacts within one three-dimensional (3D) data segment of rat iris obtained with OR-PAM imaging. We then extended the application of this algorithm to correct motions to obtain vasculature imaging in the whole mouse back. In here, we stitched five adjacent 3D data segments (large field-of-view) obtained while changing the focus of OR-PAM differently for each subarea. The results showed that the motion artifacts of both large blood vessels and microvessels could be accurately corrected in both cases. Compared to the manually stitching method and the traditional SIFT algorithm, the algorithm proposed in this paper has better performance in stitching adjacent data segments. The high accuracy of the motion correction algorithm makes it valuable in OR-PAM for high-resolution imaging of large animals and for quantitative functional imaging.

Three-dimensional Hessian matrix-based quantitative vascular imaging of rat iris with optical-resolution photoacoustic microscopy in vivo.

For the diagnosis and evaluation of ophthalmic diseases, imaging and quantitative characterization of vasculature in the iris are very important. The recently developed photoacoustic imaging, which is ultrasensitive in imaging endogenous hemoglobin molecules, provides a highly efficient label-free method for imaging blood vasculature in the iris. However, the development of advanced vascular quantification algorithms is still needed to enable accurate characterization of the underlying vasculature. We have developed a vascular information quantification algorithm by adopting a three-dimensional (3-D) Hessian matrix and applied for processing iris vasculature images obtained with a custom-built optical-resolution photoacoustic imaging system (OR-PAM). For the first time, we demonstrate in vivo 3-D vascular structures of a rat iris with a the label-free imaging method and also accurately extract quantitative vascular information, such as vessel diameter, vascular density, and vascular tortuosity. Our results indicate that the developed algorithm is capable of quantifying the vasculature in the 3-D photoacoustic images of the iris in-vivo, thus enhancing the diagnostic capability of the OR-PAM system for vascular-related ophthalmic diseases in vivo.