Integrated mechanical and structural features for photoacoustic characterization of atherosclerosis using a quasi-continuous laser

Photoacoustic method for measuring the elasticity of polydimethylsiloxane at various mixing ratios

Measuring elasticity without physical contact is challenging, as current methods often require deconstruction of the test sample. This study addresses this challenge by proposing and testing a photoacoustic effect-based method for measuring the elasticity of polydimethylsiloxane (PDMS) at various mixing ratios, which may be applied on the wide range of applications such as biomedical and optical fields. A dual-light laser source of the photoacoustic (PA) system is designed, employing cross-correlation signal processing techniques. The platform systems and a mathematical model for performing PDMS elasticity measurements are constructed. During elasticity detection, photoacoustic signal features, influenced by hardness and shapes, are analyzed using cross-correlation calculations and phase difference detection. Results from phantom tests demonstrate the potential of predicting Young's modulus using the cross-correlation method, aligning with the American Society for Testing and Materials (ASTM) standard samples. However, accuracy may be affected by mixed materials and short tubes. Normalization or calibration of signals is suggested for aligning with Young's coefficient.

Photoacoustic viscoelasticity assessment of prefrontal cortex and cerebellum in normal and prenatal valproic acid-exposed rats

Mechanical properties of brain tissues are from principal features from different points of view; diagnosis, the performance of the brain and neurological disorders. Particularly viscoelastic properties of the brain tissues are determinative. In this study based on a proposed accurate and non-invasive method, we have measured the viscoelastic properties of prefrontal cortex and cerebellum, two important brain regions involved in motor learning and pathophysiology of autism spectrum disorder (ASD). In this regard, using photoacoustic systems, viscoelastic properties of tissues from the cerebellum and prefrontal cortex of normal and prenatal VPA (Valproic acid)-exposed (i.e. autistic-like) offspring rats are measured. Results of our study show that the cerebellums of normal tissues are stiffer than the tissue obtained from autistic-like rats, while the viscoelasticity of the prefrontal cortex of normal tissues is higher than that of autistic ones. The proposed method for the measurement of viscoelastic properties of the brain tissue has the potential not only for the fundamental studies but as a diagnosis technique.

Single-Cell Photoacoustic Microrheology

Rheological properties, such as elasticity and viscosity, are fundamental biomechanical parameters that are related to the function and pathological status of cells and tissues. In this paper, an innovative photoacoustic microrheology (PAMR), which utilized the time and phase characteristics of photoacoustic (PA) response, was proposed to extract elastic modulus and viscosity. The feasibility and accuracy of the method were validated by tissue-mimicking agar-gelatin phantoms with various viscoelasticity values. PAMR realized single cell elasticity and viscosity mappings on the adipocyte and myocyte with micrometer scale. In clinical samples, normal blood cells and iron deficiency anemia cells were successfully distinguished due to their various rheological properties. This method expands the scope of conventional PA imaging and opens new possibilities for developing microrheological technology, prefiguring great clinical potential for interrogating mechanocellular properties.

Multi-parameter characterization of atherosclerotic plaques based on optical coherence tomography, photoacoustic and viscoelasticity imaging

Detection of atherosclerotic plaque vulnerability is the critical step in prevention of acute coronary events. Fibrous cap thickness, lipid core size, and inflammation extent are three key parameters for assessing plaque vulnerability. Here, we report on multimodality imaging of mice aortic plaques using a system that integrates optical coherence tomography (OCT), photoacoustic imaging (PAI), and photoacoustic viscoelasticity imaging (PAVEI). The thickness of fibrous cap is accurately evaluated by OCT, and PAI helps to determine the distribution and size of lipid core. The mechanical properties of plaques are closely related to the plaque compositions and the content and distribution of macrophages, while PAVEI can characterize the plaque viscoelasticity through the phase delay of photoacoustic signal. Experimental results demonstrate that the OCT-PAI-PAVEI system can comprehensively characterize the three traits of atherosclerotic plaques, thereby identifying high-risk lesions.

The Effect of Monophasic Pulsed Current with Stretching Exercise on the Heel Pain and Plantar Fascia Thickness in Plantar Fasciitis: A Randomized Controlled Trial

Plantar fasciitis (PF) is one of the most common causes of heel and foot pain. Monophasic pulsed current (MPC) is an electrical stimulation used to accelerate the healing processes. The purpose of this study was to determine the effect of MPC and MPC combined with plantar fascia stretching exercises (SE) on heel pain and plantar fascia thickness in treatment of PF and see if there is any relationship between heel pain and plantar fascia thickness after intervention. Forty-four participants diagnosed with PF were randomly assigned to two group; MPC group or MPC combined with plantar fascia SE. Plantar fascia thickness was measured with musculoskeletal ultrasound. Although no statistical differences between the two groups were found, heel pain and the plantar fascia thickness significantly decreased in both groups after the intervention (p < 0.001). No significant correlation was found between changes in heel pain and plantar fascia thickness after 4 weeks of treatment. Our results indicated that MPC can reduce heel pain and plantar fascia thickness caused by PF. However, MPC combined with plantar fascia SE is not superior to MCP only in terms of reduction in heel pain and plantar fascia thickening.

Assessing the development and treatment of rheumatoid arthritis using multiparametric photoacoustic and ultrasound imaging

Rheumatoid arthritis (RA), characterized by polyarthritis, is a chronic, systemic and inflammatory autoimmune disease. In this study, we developed a dual-modality multiparametric photoacoustic and ultrasound imaging technique, and successfully derived multiple parameters such as relative concentration of total hemoglobin (C_HbT ), ratio of angiogenesis, joint size and area of synovia to assess the development and treatment of RA. We established a model of adjuvant arthritis using a total number of 15 rats and randomly divided them into three groups: (a) targeted group in which the rats received targeted antirheumatic drugs; (b) nontargeted group in which the rats were treated with nontargeted antirheumatic drugs; (c) control group. We longitudinally monitored the joints of the rats in all three groups for up to 20 days and carried out quantitative analysis to evaluate the development and treatment of RA based on the derived parameters. The results suggest that the proposed dual-modality imaging technique is able to assess the effectiveness of the RA treatment using quantitative hemodynamic and morphological parameters. To show the clinical feasibility of this technique, we performed in vivo joint studies of health volunteers to visualize both structures and inside hemodynamics of the distal interphalangeal joint.

Phage display-derived oligopeptide-functionalized probes for in vivo specific photoacoustic imaging of osteosarcoma

Specific detection of various tumor types remains crucial for designing effective treatment strategies. We demonstrate photoacoustic imaging (PAI) using high-affinity and high-specificity peptide-based probes for accurate and specific diagnosis of osteosarcoma. Herein, two new tumor-specific oligopeptides, termed PT6 and PT7, were identified using phage display-based screening on an osteosarcoma cell line (UMR-106). The identified oligopeptides were able to detect clinical osteosarcoma samples on tissue microarrays. Oligopeptide-conjugated PEGylated gold nanorods (PGNR) were designed to specifically target UMR-106 cells. More importantly, PAI revealed that both PGNR-PT6 and PGNR-PT7 could bind selectively to subcutaneous UMR-106 xenografts after systemic administration and enhance the contrast of osteosarcoma images by 170% and 230%, respectively, compared to tumor-bearing mice injected with PGNRs conjugated to scrambled oligopeptides. PAI employing PGNRs conjugated to specifically designed nanoprobes may provide a new method for tumor type-specific diagnosis of osteosarcoma.

Mechanical evaluation of lipid accumulation in atherosclerotic tissues by photoacoustic viscoelasticity imaging

Photoacoustic viscoelasticity imaging (PAVEI) is a technique that directly provides the morphology of biological tissues with correlative mechanical information. In this Letter, we demonstrate the use of PAVEI to successfully characterize early-stage atherosclerotic plaques. Lipid, as the main material in early plaque lesions, embedded in gelatin was imaged to test the feasibility of PAVEI. Atherosclerosis of rabbits was studied ex vivo, and the rabbit arteries were imaged to show the intrinsic contrast of PAVEI. Our results demonstrate that PAVEI can provide valuable viscoelasticity information for early detection of atherosclerotic plaques, which yields new insights into biomechanical diagnosis of cardiovascular diseases.

Mechanical characterization of intraluminal tissue with phase-resolved photoacoustic viscoelasticity endoscopy

We developed a phase-sensitive side-scanning photoacoustic viscoelasticity endoscopy (PAVEE) for mechanical characterization of intraluminal tissues. In PAVEE, the PA phase can be extracted from the optical absorption induced ultrasonic waves and provides an index of viscoelasticity that is closely linked to tissue compositions. The transverse resolution of the PAVEE measured by carbon fiber was about 32 μm. The imaging capability of the PAVEE was verified using a vessel-mimicking phantom with different agar density. Moreover, PAVEE was investigated in processed lumen-shaped vascular tissues to evaluate the biomechanical features, which was highly consistent with the histology. The results demonstrated that the PAVEE can obtain viscoelastic properties of intraluminal tissues, which puts a new insight into the intravascular disease and holds great promise for plaque vulnerability detection.