Esophageal Findings in the Setting of a Novel Preventive Strategy to Avoid Thermal Lesions during Hybrid Thoracoscopic Radiofrequency Ablation for Atrial Fibrillation

Purpose The development of an atrio-esophageal fistula, a rare yet potentially lethal complication of ablation for atrial fibrillation, could be related to direct tissue heat transfer during and immediately after the ablation. We therefore studied the postoperative esophageal findings by esophagogastroduodenoscopy in patients that underwent a hybrid ablation procedure using a novel preventive strategy to avoid thermal lesions. Methods Thirty-four patients (28 males; 65 years ± 9 years) were retrospectively included. All underwent a hybrid ablation in our center between April 2015 and November 2019 and agreed to an esophagogastroduodenoscopy within 0–14 days (mean: 5 days) following the ablation. To reduce the incidence of thermal lesions three procedural preventive strategies were introduced: (i) videoscopic intrathoracic transesophageal echocardiographic probe visualization to understand the relationship between posterior left atrial wall and esophagus, with probe retraction before ablation; (ii) lifting the cardiac tissue away from the esophagus during energy application; and (iii) a 30-s cool-off period after energy delivery with irrigation of the device, the ablated tissue, and the surrounding tissues. Results No esophageal thermal lesions were observed. One third of patients were diagnosed with incidental esophageal findings unrelated to the ablation procedure (11; 32.4%). Conclusion Novel preventive strategies by visualization and by avoiding contact between the ablation catheter or ablated tissue and the pericardium, seems to eliminate the potential risk of esophageal thermal lesions in the setting of hybrid ablation. Since one third of patients had preexisting esophageal disease, a more comprehensive pre-operative screening could be important to reduce the risk.

УЛЬТРАСТРУКТУРНІ ОСОБЛИВОСТІ НЕЙРО-ГЛІАЛЬНО-КАПІЛЯРНИХ ВІДНОСИН СА3 ПОЛЯ ГІПОКАМПА ЧЕРЕЗ 21 ДОБУ ЗА УМОВ ЕКСПЕРИМЕНТАЛЬНОЇ ТЕРМІЧНОЇ ТРАВМИ

Severe thermal injury leads to a number of morphofunctional changes that occur in violation of integrity or loss of skin in deep burns and endogenous intoxication on the background of which significant structural and metabolic disorders in all organs and systems of the affected organism are developed. This is manifested in a complicated symptom complex of burn disease. Changes in the central nervous system play an important role in the pathogenesis of burn injury, the nature and depth of morphofunctional changes in individual cerebral structures, in particular in the hippocampus (central organ of the limbic system, which is especially sensitive to various pathogens), after thermal lesions remain poorly studied. The aim of our study was to establish the features of submicroscopic changes in the structural components of the hippocampus after 21 days under conditions of experimental thermal injury. The experimental study was performed on white laboratory male rats. Third-degree burns were applied under thiopental-sodium anesthesia with copper plates heated in boiled water to a temperature of 97–100°C. The size of the affected area was 18–20% of the rats’ body epilated surface. Histological changes were studied on the 21st day from the beginning of the experiment. For electron microscopy, the obtained ultrathin sections were contrasted with uranyl acetate and lead citrate according to the Reynolds method. It was found that on the 21st day after the experimental thermal injury significant alternative changes in neurons, glial cells and the microcirculatory tract of the hippocampus were defined which developed on the background of excessive endogenous intoxication. Neurons are hypochromic and sharply hyperchromic, disorganized and have an altered shape; there are cell-free areas. Endoplasmic reticulum, Golgi complex, mitochondria are destructively changed. Degeneration of macroglial cells has been noticed. Their nuclei are high in electron density in which heterochromatin predominates. Destruction and lysis of organelles, lysosomes have also been found in the cytoplasm. These changes of astrocytic glia lead to impaired trophic function and the relation between astrocytes and blood capillaries. Hemocapillaries wall remodeling is manifested by the total edema, compaction of the basement membrane. The lumenal surface of the plasmolemma of endothelial cells is homogeneous, indistinctly contoured. The cytoplasm of endothelial cells is swollen, enlightened, and poor in organelles; there is a small number of micropinocytic bubbles and vesicles.

Biomedical applications of photoacoustics for thermal therapy

This work demonstrates the feasibility of Photoacoustic tomography (PAT) and real-time photoacoustic (PA) monitoring using a single transducer prototype system to detect and/or monitor tumour growth using low absorbing targets embedded in turbid phantom and thermal lesions in tissue. A single transducer PA prototype system is build utilizing a laser system producing light in the near infra-red while untrasonic transducers detects the PA pressure waves generated. The ability to image tissue using PAT is initially demonstrated using gelatin phantoms with targets of similar optical properties to native and coagulated prostate tissue. Next, lesions in bovine muscle tissue and bovine liver are also imaged demonstrating the effectiveness of PAT tp detect lesions during thermal therapy (TT). Selective imaging is shown by varying the optical wavelength to preferentially absorb light and target specific structures which in turn produce high contrast after image reconstruction. Finally, the capability of using PA to monitor TT is explored by measuring the changes in the optical and mechanical properties of tissue equivalent albumen phantoms as a function of thermal dose on PA signals, thereby demonstrating the real time capability of this modality to monitor TT.

Biomedical applications of photoacoustics for thermal therapy

This work demonstrates the feasibility of Photoacoustic tomography (PAT) and real-time photoacoustic (PA) monitoring using a single transducer prototype system to detect and/or monitor tumour growth using low absorbing targets embedded in turbid phantom and thermal lesions in tissue. A single transducer PA prototype system is build utilizing a laser system producing light in the near infra-red while untrasonic transducers detects the PA pressure waves generated. The ability to image tissue using PAT is initially demonstrated using gelatin phantoms with targets of similar optical properties to native and coagulated prostate tissue. Next, lesions in bovine muscle tissue and bovine liver are also imaged demonstrating the effectiveness of PAT tp detect lesions during thermal therapy (TT). Selective imaging is shown by varying the optical wavelength to preferentially absorb light and target specific structures which in turn produce high contrast after image reconstruction. Finally, the capability of using PA to monitor TT is explored by measuring the changes in the optical and mechanical properties of tissue equivalent albumen phantoms as a function of thermal dose on PA signals, thereby demonstrating the real time capability of this modality to monitor TT.

Photoacoustic Detection and Optical Spectroscopy of High-Intensity Focused Ultrasound-Induced Thermal Lesions in Biologic Tissue

In this study, the capability of a photoacoustic (PA) method in detecting high-intensity focused ultrasound (HIFU) thermal lesions was investigated in chicken breast tissue in vitro and the optical properties of the HIFU-treated and native tissues were determined. Created with a 1-MHz HIFU transducer, the detectability of the induced thermal lesions was assessed photoacoustically at 720 and 845 nm and their optical properties were characterized in the wavelength range 500-900 nm. The results show that the averaged ratio of the peak-to-peak PA signal amplitude of HIFU-treated tissue to that of native tissue is more than 3 fold. The optical spectroscopy investigation revealed that the absorption and reduced scattering coefficients are higher for HIFU-treated tissues than native tissues. This work demonstrates the capability of the PA method in detecting HIFU-induced thermal lesions due, in part, to the increase in their optical absorption coefficient, reduced scattering coefficient, and deposited laser energy fluence.

Photoacoustic Detection and Optical Spectroscopy of High-Intensity Focused Ultrasound-Induced Thermal Lesions in Biologic Tissue

In this study, the capability of a photoacoustic (PA) method in detecting high-intensity focused ultrasound (HIFU) thermal lesions was investigated in chicken breast tissue in vitro and the optical properties of the HIFU-treated and native tissues were determined. Created with a 1-MHz HIFU transducer, the detectability of the induced thermal lesions was assessed photoacoustically at 720 and 845 nm and their optical properties were characterized in the wavelength range 500-900 nm. The results show that the averaged ratio of the peak-to-peak PA signal amplitude of HIFU-treated tissue to that of native tissue is more than 3 fold. The optical spectroscopy investigation revealed that the absorption and reduced scattering coefficients are higher for HIFU-treated tissues than native tissues. This work demonstrates the capability of the PA method in detecting HIFU-induced thermal lesions due, in part, to the increase in their optical absorption coefficient, reduced scattering coefficient, and deposited laser energy fluence.

Ultrasound shear wave elastography: numerical modeling and time-frequency analysis with an application in HIFU thermal lesion detection

In this work, a new numerical framework is proposed and implemented to simulate acoustic wave propagation in 3D viscoelastic heterogeneous media. The framework is based on the elastodynamic wave equation in which a 3D second-order time-domain perfectly matched layer (PML) formulation is developed to model unbounded media. The numerical framework is discretized by a finite difference formulation and its stability analysis is discussed. The proposed numerical method is capable of simulating 3D shear and longitudinal acoustic waves for arbitrary source geometries and excitations, together with arbitrary initial and boundary conditions. After validation of the framework, it was used to simulate the propagation of ultrasound shear wave in high intensity focused ultrasound (HIFU) induced thermal lesions located within soft tissue. The parameters in these simulations were obtained from standard double-indentation measurements of the viscoelastic parameters of normal and thermally coagulated chicken breast tissue samples. A HIFU system was used to induce thermal lesions in tissue. In this study, a new elastography procedure was also introduced to differentiate between the normal and HIFU induced thermal lesions. This method is based on time-frequency analysis of shear wave propagation within the tissue. In the proposed method, the Wigner-Ville distribution has been used as a time-frequency analytical technique to detect the location of shear wave propagating within the tissue, and to estimate the shear speed of the wave as well as its center frequency and attenuation coefficient. This method was applied to the acoustic wave propagation simulation results of the HIFU thermal lesion. It was finally used to estimate the local viscoelastic parameters of the medium. It was demonstrated that the proposed method is capable of differentiating the thermal lesions from the normal tissue based on their viscoelastic parameters.

Ultrasound shear wave elastography: numerical modeling and time-frequency analysis with an application in HIFU thermal lesion detection

In this work, a new numerical framework is proposed and implemented to simulate acoustic wave propagation in 3D viscoelastic heterogeneous media. The framework is based on the elastodynamic wave equation in which a 3D second-order time-domain perfectly matched layer (PML) formulation is developed to model unbounded media. The numerical framework is discretized by a finite difference formulation and its stability analysis is discussed. The proposed numerical method is capable of simulating 3D shear and longitudinal acoustic waves for arbitrary source geometries and excitations, together with arbitrary initial and boundary conditions. After validation of the framework, it was used to simulate the propagation of ultrasound shear wave in high intensity focused ultrasound (HIFU) induced thermal lesions located within soft tissue. The parameters in these simulations were obtained from standard double-indentation measurements of the viscoelastic parameters of normal and thermally coagulated chicken breast tissue samples. A HIFU system was used to induce thermal lesions in tissue. In this study, a new elastography procedure was also introduced to differentiate between the normal and HIFU induced thermal lesions. This method is based on time-frequency analysis of shear wave propagation within the tissue. In the proposed method, the Wigner-Ville distribution has been used as a time-frequency analytical technique to detect the location of shear wave propagating within the tissue, and to estimate the shear speed of the wave as well as its center frequency and attenuation coefficient. This method was applied to the acoustic wave propagation simulation results of the HIFU thermal lesion. It was finally used to estimate the local viscoelastic parameters of the medium. It was demonstrated that the proposed method is capable of differentiating the thermal lesions from the normal tissue based on their viscoelastic parameters.

Examination of Contrast Mechanisms in Optoacoustic Imaging of Thermal Lesions

Examination of Contrast Mechanisms in Optoacoustic Imaging of Thermal Lesions