We present a novel metal reflector based illumination strategy for optimized thermoacoustic tomography (TAT) of intracerebral hemorrhage (ICH). The strategy can capture stray microwave energy from the imaging area, redirects it synchronously to brain tissues, disrupts original electric (E)-field boundary conditions, and reshapes the E-field distribution into uniformity. This renders TAT more dependent on inherent dielectric property differences of brain tissues than external E-field variations, thereby enhancing image quality. Numerical simulations were performed to evaluate the reflector dimensions, and it was determined that a half-wavelength diameter reflector provided an optimal performance, achieving minimal E-field intensity deviation, optimal energy absorption density in brain tissue, and superior lesion-to-tissue contrast. Based on the optimal parameters from the simulations, a metal reflector was fabricated and integrated into the TAT system for in vivo detection in normal and ICH rats. Imaging of rat brain was then conducted and demonstrated that the reflector enhanced TAT significantly improved tissue boundary definition, hemorrhage/edema visibility, image sharpness/contrast and intergroup symmetry differences. The TAT image quality is further improved when an image reconstruction algorithm integrating logarithmic depth weighting with multi-scale Retinex is used. Anatomical photographs and HE-stained pathological examinations and MRI scans of the brain tissue imaged proved these TAT imaging findings. The reflector-optimized strategy has low cost and high system compatibility. This study suggests that our reflector-based TAT may offer a new yet practical tool for in vivo dielectric brain research and auxiliary diagnostics of neurological diseases.

Accurate multimodal registration between magnetic resonance imaging (MRI) and photoacoustic tomography (PAT) is essential for localizing functional hemodynamic signals to specific neuroanatomical structures, such as the hippocampus, in preclinical brain studies. However, the inherently low soft-tissue contrast and high noise characteristics of PAT images render precise alignment challenging. Existing registration methods typically rely on global optimization and lack the structural priors necessary for localizing small and complex regions like the $\mathbf{C}$ shaped hippocampus. To address the challenge of aligning MRI and PAT images under significant modality differences and lowcontrast conditions, this paper proposes a structural priorconstrained method for MRI-PAT brain image registration and segmentation. First, the SAM-Med2D model is employed to segment MRI images and generate hippocampal region masks, which are introduced as structural priors into the registration process to enhance constraints on small target regions. Second, ORB feature matching combined with the RANSAC algorithm is utilized to estimate affine transformation parameters, using the superior sagittal sinus as a reference anchor to achieve initial cross-modal alignment. Building upon this, a structural consistency constraint term is constructed to optimize PAT segmentation results and improve structural overlap. Experimental results on mouse brain MRI-PAT data demonstrate that the proposed method improves alignment accuracy and enhances structural consistency in the hippocampal region. This work provides a robust solution for integrating structural and functional imaging data in small animal studies.

Background: Sleep deprivation (SD) has been increasingly recognized for its detrimental effects on human health, particularly its severe damage to brain tissue. Photoacoustic tomography (PAT), hybrid imaging modalities combining light and sound, enable real-time, high-spatial-resolution imaging to rapidly capture SD-induced alterations in cerebral oxygen metabolism. Objective: To investigate the impact of SD on survival and analyze cerebral oxygen metabolic changes as potential predictors of mortality. Methods: A custom-built photoacoustic tomography system was employed to scan the hippocampal coronal plane of SD mice. Twenty-three mice were randomly assigned to three groups: sustained SD (SSD, n=9), intermittent SD (ISD, n=7), and control (n=7). The SSD group underwent continuous sleep deprivation (20-hour deprivation starting daily at 9:00 AM, 4-hour rest, repeated in 72-hour cycles followed by 24-hour rest/data collection). The ISD group alternated between 72-hour deprivation cycles, 24-hour rest/data collection and 72-hour rest periods. PAT data were collected every 72 hours later to monitor cerebral oxygen metabolism. Results: After 18 deprivation cycles, significant survival differences were observed among groups (Logrank P=0.005), with the SD group showing the highest mortality. PAT data revealed that deceased mice exhibited significantly lower photoacoustic signals for oxygenated hemoglobin (HbO(2)) (P=0.02) and oxygen saturation (sO(2)) (P=0.001) compared to survivors in their final scans, while deoxygenated hemoglobin (HbR) showed no difference (P=0.147). Conclusion: Prolonged sleep deprivation directly accelerates mortality, with cumulative deprivation duration correlating positively with mortality risk. HbO(2) and sO(2) may serve as potential early warning indicators for SD-induced fatal outcomes.

Thyroid cancer has emerged as a globally prevalent malignancy, exhibiting a continuously rising incidence rate. While conventional ultrasound (US) is the current primary screening modality, its reliance on morphological features often results in insufficient specificity and consequent over-biopsies. This study introduces an ultrasound-multispectral photoacoustic (PAUS) dual-modality imaging system. Using a multi-wavelength (760-930 nm) spectral unmixing algorithm, it accurately resolves key molecular components including oxyhemoglobin (HbO), deoxyhemoglobin (HbR), total hemoglobin (HbT), and oxygen saturation (sO(2)). A feature-level fusion algorithm integrates PA and ultrasound images, incorporating spatial registration and an adaptive weighting strategy to achieve complementary voxel-level features across modalities. This facilitates comprehensive in vivo quantitative analysis of thyroid nodules, yielding multi-parametric structural-functional data to aid in benign-malignant differentiation. Clinical in vivo PAUS data were acquired from thyroid nodule cases and validated against conventional US and normal thyroid tissue.

As the largest organ of the human body, the skin serves as the first barrier protecting the body from external harm. Current diagnostic methods for skin diseases primarily rely on visual inspection by physicians and skin biopsies, but these approaches have significant limitations and cannot comprehensively evaluate vascular functional changes in skin lesion areas. This study proposes a non-invasive skin detection method based on Multispectral Photoacoustic Tomography (MSOT), enabling real-time, high-resolution three-dimensional (3D) imaging of the skin to provide high-volume structural and functional information. Using an MSOT system, we imaged melanocytic nevi and acne lesions on volunteers' skin, clearly observing the distribution of melanocytic nevi and presenting their spatial structure within the skin through 3D reconstruction. Additionally, 3D Photoacoustic scanning of acne lesions revealed significantly enhanced Photoacoustic signals around acne sites compared to normal skin, particularly in inflamed regions. This enhancement primarily originates from local vasodilation and increased blood flow. Through multispectral reconstruction, we quantitatively analyzed hemodynamic parameters (HbR, HbO, water content, and sO(2)) in acne areas, identifying significant differences between lesion regions and normal skin. Furthermore, an optical flow algorithm based on blood spatial heterogeneity was employed to measure blood flow velocity in acne lesions, demonstrating that flow velocity in these areas was significantly higher than in normal skin. These results highlight the powerful capabilities of MSOT in detecting and evaluating skin lesions, positioning it as a promising tool for the diagnosis and management of skin diseases.

Objective This study aims to develop a microwave-induced thermoacoustic and ultrasound dual-modality microscopy system that integrates the advantages of both imaging techniques to investigate the dielectric properties of biological tissues at a microscopic level. Methods This paper first discusses a method to enhance system resolution by combining short-pulse microwave excitation with high-frequency point-focused ultrasonic transducer detection. A three-dimensional microwave-induced thermoacoustic microscopic imaging system was constructed based on this approach and further developed into a dual-modality system capable of both thermoacoustic and ultrasonic imaging. The image reconstruction and dual-modality image fusion strategies are also described. Subsequently, experiments were conducted in the following sequence: imaging of copper wires to evaluate the system's spatial resolution along the X/Y/Z axes; imaging of tubes containing 3% and 6% saline solutions and tubes filled with coupling agent/vegetable oil to demonstrate the complementary information provided by the two modalities; imaging of brain tissue and bone-cartilage samples to assess the applicability of the technology; and osteoporosis detection to validate the disease diagnostic capability of the dual-modality system. The microwave-induced thermoacoustic and ultrasound microscopic images of these samples were verified against corresponding photographs or micro-CT images. Results The thermoacoustic and ultrasonic images of the copper wire closely matched the physical photograph. The three-dimensional resolutions of the microwave-induced thermoacoustic and ultrasound imaging systems, as estimated from the copper wire experiment, were 178x178x88 mu m3 and 177x177x42 mu m3, respectively. These measured values align well with theoretical predictions. The dual-modality imaging system successfully combines dielectric property differences captured by thermoacoustic imaging and acoustic impedance variations captured by ultrasound imaging, thereby providing both functional and structural information of the samples. Specifically, the system distinguished between tubes containing saline solutions of different concentrations and those containing vegetable oil, demonstrating strong spatial consistency with physical photographs. The thermoacoustic image contrast among saline solutions corresponded to theoretical dielectric properties, while the ultrasonic contrast between saline and oil reflected their difference in acoustic impedance. The system identified multiple brain tissue structures, including the cortex, hippocampus, superior colliculus, corpus callosum, cingulate cortex, and striatum. The bimodal imaging approach exhibited superior performance, visualizing tissue structures with greater clarity and detail than either modality alone. The brain tissue images were consistent with physical photographs, tissue dielectric properties, and publicly available anatomical atlases. The bimodal system clearly delineated cartilage and epiphyseal lines via thermoacoustic imaging, while ultrasonic imaging revealed bone structures. Thermoacoustic imaging alone differentiated bone sections between normal and osteoporotic groups; however, incorporating prior skeletal contour information from ultrasound significantly enhanced discriminatory power, resulting in intergroup differences with higher statistical significance. The imaging results of bone samples corresponded well with physical photographs, micro-CT images, and theoretical analyses of dielectric properties for cartilage, normal bone, and osteoporotic bone. Conclusion The microwave-induced thermoacoustic and ultrasound dual-modality microscopy system developed in this study demonstrates potential for microscopic detection of complex biological tissues based on dielectric properties. It is expected to provide a new imaging tool for functional assessment of brain tissue and the skeletal system, as well as for studies on disease pathogenesis.

Photoacoustic imaging (PAI) has emerged as a transformative modality for bridging traditional Chinese medicine (TCM) theory and contemporary biomedical research in acupuncture mechanism studies. This review assesses PAI’s capacity to decode acupuncture-induced neuromodulatory and hemodynamic effects, with dual focus on the central nervous system (CNS) responses and acupoint-specific microcirculatory dynamics. Leveraging the photoacoustic effect coupled with ultrasonic detection, PAI enables non-invasive, high-resolution mapping of cerebral hemodynamic parameters, including blood flow, oxygen saturation and hemoglobin concentrations, in real time. Experimental evidence from murine models of cerebral hypoperfusion and ischemic stroke demonstrates acupoint-specific spatiotemporal activation patterns, particularly at Yongquan (KI1) and Yanglingquan (GB34), revealing cortical hemodynamic reorganization and angiogenesis. At the microcirculatory level, PAI identifies functional transitions from quiescent to activated vascular states during disease progression, characterized by altered perfusion dynamics and vascular permeability. While structural metrics (e.g., microvascular density and curvature) show no significant differences in knee osteoarthritis models, functional parameters such as hemoglobin flux and oxygen metabolism emerge as critical biomarkers of acupoint specificity. PAI further enhances treatment precision through standardized acupoint localization, as evidenced by electrostimulation studies at Hegu (LI4) and Zhongwan (CV12). This synthesis highlights PAI’s dual contributions: (1) validating CNS-mediated systemic regulation via acupoint-brain functional correlations, and (2) providing multimodal quantification of microcirculatory dynamics. Future directions emphasize integration of molecular probes for neuroendocrine pathway visualization and multimodal imaging to address unresolved thermal/optical interactions. By synergizing TCM principles with advanced biophotonics, PAI establishes a paradigm for mechanistic acupuncture research and clinical translation.

BACKGROUND:Sarcopenia, a significant geriatric syndrome, faces challenges in accurate diagnosis due to limitations of current imaging techniques. This study explores the novel application of multispectral optoacoustic tomography (MSOT) in evaluating sarcopenia, focusing on quantifying oxygen dynamics and collagen distribution in skeletal muscles. METHODS:We conducted MSOT imaging on the lower limbs of senescence-accelerated mouse prone 8 (SAMP8; n = 14) and senescence-accelerated mouse resistant 1 (SAMR1; n = 8) models, using light wavelengths of 760, 840 and 930 nm. CT, histopathology and immunofluorescence were used for cross-validation. RESULTS:Label-free MSOT imaging directly visualized muscle structure and metabolism with high spatiotemporal resolution. Compared to SAMR1 controls, sarcopenic SAMP8 mice demonstrated 23.8% lower HbO2 levels (SAMP8: 0.0016 ± 0.0003 a.u. vs. SAMR1: 0.0021 ± 0.0005 a.u.; p = 0.018) and reduced metabolic activity in skeletal muscles. SAMP8 mice also revealed 43.2% higher collagen content (SAMP8: 3.451 ± 1.159 a.u. vs. SAMR1: 2.409 ± 0.635 a.u.; p = 0.030) alongside more disordered muscle structure, suggesting increased fibrosis. An inverse correlation was observed between computed tomography (CT) values and MSOT-derived collagen signals (r = -0.789, p < 0.001), whereas no such correlation existed with HbO2, indicating that MSOT provides unique metabolic insights beyond traditional imaging techniques. CONCLUSIONS:This first application of MSOT in sarcopenia research highlights its potential as a noninvasive, real-time tool for early diagnosis, therapeutic evaluation and mechanistic understanding. Its ability to detect metabolic changes not captured by CT underscores its complementary role in comprehensive muscle assessment. Future research should focus on longitudinal studies and clinical translation.

With the advancement of modernization of traditional Chinese medicine (TCM) modernization and the development of computer and image processing technologies, there is a growing demand for objective and digital tongue diagnosis. While traditional tongue examination methods can partially achieve objective analysis of tongue color and texture, they have difficulty obtaining deep vascular networks and metabolic information of the tongue. To overcome this limitation, this study proposes a novel dynamic tongue monitoring method based on photoacoustic tomography (PAT), combined with multispectral photoacoustic quantitative algorithms, enabling real-time dynamic monitoring of tongue hemodynamics. Through continuous PAT monitoring of tongue changes in diabetic rats, we confirmed significant differences in hemodynamic parameters between diabetic and normal groups, mainly characterized by decreased oxyhemoglobin (HbO), increased deoxyhemoglobin (HbR), and significantly reduced oxygen saturation (sO(2)). By analyzing changes in tongue hemodynamic parameters, this study identifies the abnormal photoacoustic characteristics of diabetic tongues, providing quantitative evidence for TCM tongue diagnosis and promoting the objective and standardized development of TCM diagnostics.

Photoacoustic Imaging (PAI), as a biomedical imaging technology, boasts remarkable features containing exceptional resolution and outstanding contrast. However, when lasers propagate through biological tissues, its energy rapidly attenuates with distance. Consequently, the photoacoustic (PA) signal becomes weak, resulting in worse contrast and resolution of the PA image. To address this challenge, we develop the multi-scale retinex (MSR) algorithm for enhancing PA images. Subsequently, the MSR algorithm was utilized in animal and human experiments. And the enhanced images were quantitative analyzed by information entropy, contrast and brightness. The results indicate a significant improvement in both contrast and resolution of the PA images enhanced by the MSR algorithm.

In photoacoustic imaging (PAI), a delay-and-sum (DAS) beamforming reconstruction algorithm is widely used due to its ease of implementation and fast execution. However, it is plagued by issues such as high sidelobe artifacts and low contrast, that significantly hinder the ability to differentiate various structures in the reconstructed images. In this study, we propose an adaptive weighting factor called spatial coherence mean-to-standard deviation factor (scMSF) in DAS, which is extended into the spatial frequency domain. By combining scMSF with a minimum variance (MV) algorithm, the clutter level is reduced, thereby enhancing the image contrast. Quantitative results obtained from the phantom experiment demonstrate that our proposed method improves contrast ratio (CR) by 30.15 dB and signal-to-noise ratio (SNR) by 8.62 dB compared to DAS while also improving full-width at half maxima (FWHM) by 56%. From the in-vivo experiments, the scMSF-based reconstruction image exhibits a higher generalized contrast-to-noise ratio (gCNR), indicating improved target detectability with a 25.6% enhancement over DAS and a 22.5% improvement over MV.

Photoacoustic tomography (PAT) was utilized to investigate the hemodynamics effects of Chuanxiong in localized regions of mice. A four-day continuous gavage was administered to healthy mice (n=10), followed by data acquisition using PAT. It was observed that Chuanxiong influenced the concentration of total hemoglobin (HbT) in the brains and legs of mice. These results suggest a consistent impact of Chuanxiong on HbT concentration across various regions in mice, highlighting the potential of PAT in advancing our understanding of the action mechanisms of Chinese herbal medications and enhancing their clinical applications.

BackgroundTo investigate the relationship between the triglyceride and glucose (TyG) index and cognitive impairment (CI).MethodsFive authoritative databases were systematically searched for potentially relevant studies on ‘TyG index’ and ‘CI’ from inception to 27 April 2024. Two representative databases from the United Kingdom and United States were also included. We used the PICOS criteria to select available articles. All data was combined to compute Odd Ratios (ORs).Results15 studies were included in the meta-analysis (participants: 5604303). The pooled effect sizes demonstrate that individuals with a high TyG index exhibit a significantly elevated risk of CI compared to those with a low TyG index (OR = 2.16, 95%CI: 1.51; 3.08, p < 0.001). The subgroup analysis showed that inpatients with a high TyG index exhibited an increased risk of CI (OR = 4.56, 95%CI: 3.09; 6.74, p < 0.001). Furthermore, the risk of developing distinct types of CI differed significantly [CI: OR = 1.64, 95% CI: 1.29; 2.07, p < 0.001; Vascular Cognitive Impairment (VCI): OR = 5.39, 95% CI: 3.33; 8.70, p < 0.001].ConclusionA positive correlation exists between the TyG index and risk of CI, which has potential value in optimizing CI risk stratification among elderly people, especially those hospitalized.Systematic review registrationhttps://www.crd.york.ac.uk/prospero/, identifier CRD42023450336.

Traditional diagnostic techniques including visual examination, ultrasound (US), and magnetic resonance imaging (MRI) have limitations of in-depth information for the detection of nail disorders, resolution, and practicality. This pilot study, for the first time, evaluates a dual-modality imaging system that combines photoacoustic tomography (PAT) with the US for the multiparametric quantitative assessment of human nail. The study involved a small cohort of five healthy volunteers who underwent PAT/US imaging for acquiring the nail unit data. The PAT/US dual-modality imaging successfully revealed the fine anatomical structures and microvascular distribution within the nail and nail bed. Moreover, this system utilized multispectral PAT to analyze functional tissue parameters, including oxygenated hemoglobin, deoxyhemoglobin, oxygen saturation, and collagen under tourniquet and cold stimulus tests to evaluate changes in the microcirculation of the nail bed. The quantitative analysis of multispectral PAT reconstructed images demonstrated heightened sensitivity in detecting alterations in blood oxygenation levels and collagen content within the nail bed, under simulated different physiological conditions. This pilot study highlights the potential of PAT/US dual-modality imaging as a real-time, noninvasive diagnostic modality for evaluating human nail health and for early detection of nail bed pathologies.

Tissue dielectric properties can vary upon the incident of an acoustic wave. The goal of this study is to quantify this change due to the acoustoelectric effect (AE), and to obtain the frequency-dependent dielectric properties of tissues exposed to low-intensity focused ultrasound (LIFU). The dielectric properties of the blood, brain, chest muscle, heart, kidney, leg muscle, liver, lung, pancreas, and spleen of rats were measured by an open-ended coaxial probe method. The acoustic intensity of LIFU focus was 2.97 MPa (67.6 W/cm2), 3.95 MPa (120 W/cm2), and 5.17 MPa (204 W/cm2), respectively, and the measurement frequency band was 0.1–7.08 GHz. The measurement results show that with the LIFU modulation, the conductivity and dielectric constant decreased in the high-frequency band, and on the contrary, they increased in the low-frequency band, and the larger the acoustic intensity was, the more obvious the phenomenon was. This work contributes to a better understanding of the mechanisms by which ultrasound acts on the dielectric properties of biological tissues. It is expected that the findings from this study will provide a basis that the response of tissue to LIFU modulation can be monitored by noninvasive techniques such as microwave-induced thermoacoustic imaging (MTI) and microwave imaging, present a new idea for improving the endogenous contrast between different biological tissues in MTI and acoustoelectric imaging, and possibly lead to the development of a new imaging method based on the relaxation time of tissue after LIFU modulation.

This study aims to explore the feasibility of fine-needle aspiration biopsy (FNAB) under dual modal photoacoustic tomography(PAT)/ultrasound (US) imaging. A total of 25 patients who have thyroid nodules with thyroid imaging reporting and data system (TIRADS) 3 and 4 (malignant risk <85%) were recruited. The specimens obtained from the PAT/US-guided FNAB were collected for cytology analysis. Cytological diagnoses for the 25 patients were classified in perspective of the Bethesda system for reporting thyroid cytopathology diagnostic category (DC) I: 4%(1/25); DC II: 12% (3/25); DC III: 20% (5/25); DC IV: 8% (2/25); DC V: 32% (8/25); and DC VI: 24% (6/25). The DC I nodule exhibited inadequate cytology and had structural characteristic of predominant calcifications in PAT/US mapping. The DC V-VI nodules showed lower photoacoustic (PA) signals compared to the DC I-IV nodules. Regions with a high PA signal demonstrated a significant number of erythrocytes in FNAB cytology. Moreover, nodules with microcalcifications did not show a significant difference compared to their surroundings in the PA signal, while nodules with macrocalcifications gave higher PA signals compared to their surroundings. The conclusions are as follows: combining US with PAT can evaluate the structure and function of thyroid nodules in vivo. This study demonstrates that dual modal PAT/US imaging has the potential to be an effective clinical tool to guide FNAB of thyroid nodules.

为解决传统微波热声成像技术对含有骨骼的复杂生物组织难以完整清晰重建的问题, 本文提出新型双频微波热声成像技术. 即利用两个不同中心频率短脉宽微波激励组织得到两组单频微波热声数据, 两组数据利用区域像素均值与区域吸收系数补偿进行能量校准后, 以骨骼在不同频率下微波能量吸收系数的比值进行加权相减, 最后得到减小骨骼副作用的双频微波热声图像. 本文首先对双频微波热声成像方法的原理进行了研究, 然后介绍了搭建的双频微波热声成像系统, 最后进行了兔膝关节与鸡跖骨成像实验, 并对成像结果进行了定性观察与半定量量化分析. 实验结果表明, 与单频微波热声成像相比, 双频微波热声成像中的组织估算尺寸和微波热声信号趋势与相应的组织实际尺寸和理论分析更加符合. 双频微波热声成像技术能够减小骨骼的“负造影”作用带来的影响, 从而使受此作用影响的半月板、交叉韧带和骨髓腔清晰完整重建. 综上, 此方法能够提高微波热声成像技术对含骨复杂生物组织的成像能力, 从而推动相关应用研究的进展, 并为需要缓解骨骼副作用的其它影像学方法提供参考.

Photoacoustic imaging (PAI) is an emerging biomedical imaging modality, offering numerous advantages, including high resolution and high contrast. In its application to brain imaging, however, the photoacoustic (PA) signals from brain tissue weaken considerably due to the distortion effects of the skull. This attenuation reduces the resolution and contrast significantly. To address this issue, here we describe a Log-MSR algorithm that combines the logarithmic depth logarithmic enhancement (Log) algorithm and the multi-scale Retinex (MSR) algorithm. In this method, the Log algorithm performs local weighted compensation based on signal attenuation for different depths, while the MSR algorithm improves the contrast of the image. The proposed Log-MSR algorithm was tested and validated using several phantom and in vivo experiments. The enhanced images constructed by the Log-MSR algorithm were qualitatively and quantitatively analyzed in terms of brain structure and function. Our results show that the Log-MSR algorithm may provide a significant enhancement to photoacoustic imaging of deep brain tissue.

Background:Tumor radiotherapy combined with immunotherapy for solid tumors has been proposed, but tumor vascular structure abnormalities and immune microenvironment often affect the therapeutic effect of tumor, and multimodal imaging technology can provide more accurate and comprehensive information in tumor research. The purpose of this study was to evaluate the dynamic monitoring of tumor blood vessels and microenvironment induced by radiotherapy by magnetic resonance/photoacoustic (MR/PA) imaging, and to explore its application value in radiotherapy combined with immunotherapy.Methods:The tumor-bearing mice were randomly allocated into six groups, which received different doses of radiation therapy (2 Gy ×14 or 8 Gy ×3) and anti-programmed death ligand-1 (PD-L1) antibody for two consecutive weeks. MR/PA imaging was used to noninvasively evaluate the response of tumor to different doses of radiotherapy, combined with histopathological techniques to observe the tumor vessels and microenvironment.Results:The inhibitory effect of high-dose radiotherapy on tumors was significantly greater than that of low-dose radiotherapy, with the MR images revealing that the signal intensity decreased significantly (P<0.05). Compared with those in the other groups, the tumor vascular density decreased significantly (P<0.01), and the vascular maturity index increased significantly in the low-dose group (P<0.05). The PA images showed that the deoxyhemoglobin and total hemoglobin levels decreased and the SO2 level increased after radiation treatment (P<0.05). In addition, the high-dose group had an increased number of tumor-infiltrating lymphocytes (CD4+ T and CD8+ T cells) (P<0.01, P<0.05) and natural killer cells (P<0.001) and increased PD-L1 expression in the tumors (P<0.05). The combination of radiotherapy and immunotherapy increased the survival rate of the mice (P<0.05), and a regimen of an 8 Gy dose of radiation combined with immunotherapy inhibited tumor growth and increased the survival rate of the mice to a greater degree than the 2 Gy radiation dose with immunotherapy combination (P=0.002).Conclusions:Differential fractionation radiotherapy doses exert biological effects on tumor vascular and the immune microenvironment, and MR/PA can be used to evaluate tumor vascular remodeling after radiotherapy, which has certain value for the clinical applications of radiotherapy combined with immunotherapy.

BACKGROUND:Electrical conductivity directly correlates with tissue functional information such as blood and water contents, and quantitative extraction of tissue conductivity is of significant importance for disease detection and diagnosis using microwave-induced thermoacoustic tomography (TAT).OBJECTIVE:The existing quantitative TAT (qTAT) approaches capable of extracting tissue conductivity require two steps for the recovery of conductivity. Such two steps approaches depend on an accurate knowledge of the microwave energy loss distribution in tissue and offer a slow computational convergence rate. The purpose of this study is to develop a new algorithm to reconstruct tissue conductivity with higher reconstruction accuracy and greater computational efficiency.METHODS:We propose an improved qTAT method for direct recovery of tissue conductivity from thermoacoustic data measured along the boundary with only one step without the dependence of microwave energy loss information. The feasibility of our one-step qTAT method is validated in both simulated and tissue-mimicking phantom experiments with single-target and multi-target configurations with different contrast levels.RESULTS:Compared with the previous two-step methods, our one-step qTAT method improves the accuracy of conductivity recovery with approximately one-fold reduction in the mean absolute error (MAE) and root mean square error (RMSE) with p-values greater than 0.05. In addition, the convergence rate is improved by more than two folds for the one-step method.CONCLUSIONS:The study demonstrates that new method can quantitatively reconstruct conductivity of tissue more accurately and efficiently over the existing qTAT methods, leading to potentially enhanced accuracy for disease detection and diagnosis.