Histotripsy Liquefaction of Large Hematoma for Intracerebral Hemorrhage Using Millisecond-Length Ultrasound Pulse Groups Combined With Fundamental and Second Harmonic Superposition: A Preliminary Study

Histotripsy: an innovative approach for minimally invasive tumour and disease treatment

Histotripsy is a noninvasive medical technique that uses high-intensity focused ultrasound (HIFU) to treat liver tumours. The two main histotripsy methods are boiling histotripsy and cavitation cloud histotripsy. Boiling histotripsy uses prolonged ultrasound pulses to create small boiling bubbles in the tissue, which leads to the breakdown of the tissue into smaller subcellular fragments. Cavitation cloud histotripsy uses the ultrasonic cavitation effect to disintegrate target tissue into precisely defined liquefied lesions. Both methods show similar treatment effectiveness; however, boiling histotripsy ensures treatment stability by producing a stable boiling bubble with each pulse. The therapeutic effect is ascribed to mechanical damage at the subcellular level rather than thermal damage. This article discusses the mechanisms, treatment parameters, and potential of histotripsy as a minimally invasive procedure that provides precise and controlled subcellular damage.

Ultrasound image segmentation using Gamma combined with Bayesian model for focused-ultrasound-surgery lesion recognition

This study aims to investigate the feasibility of combined segmentation for the separation of lesions from non-ablated regions, which allows surgeons to easily distinguish, measure, and evaluate the lesion area, thereby improving the quality of high-intensity focused-ultrasound (HIFU) surgery used for the non-invasive tumor treatment. Given that the flexible shape of the Gamma mixture model (GΓMM) fits the complex statistical distribution of samples, a method combining the GΓMM and Bayes framework is constructed for the classification of samples to obtain the segmentation result. An appropriate normalization range and parameters can be used to rapidly obtain a good performance of GΓMM segmentation. The performance values of the proposed method under four metrics (Dice score: 85%, Jaccard coefficient: 75%, recall: 86%, and accuracy: 96%) are better than those of conventional approaches including Otsu and Region growing. Furthermore, the statistical result of sample intensity indicates that the finding of the GΓMM is similar to that obtained by the manual method. These results indicate the stability and reliability of the GΓMM combined with the Bayes framework for the segmentation of HIFU lesions in ultrasound images. The experimental results show the possibility of combining the GΓMM with the Bayes framework to segment lesion areas and evaluate the effect of therapeutic ultrasound.

On-demand regulation and enhancement of the nucleation in acoustic droplet vaporization using dual-frequency focused ultrasound

Acoustic droplet vaporization (ADV) plays an important role in focused ultrasound theranostics. Better understanding of the relationship between the ultrasound parameters and the ADV nucleation could provide an on-demand regulation and enhancement of ADV for improved treatment outcome. In this work, ADV nucleation was performed in a dual-frequency focused ultrasound configuration that consisted of a continuous low-frequency ultrasound and a short high-frequency pulse. The combination was modelled to investigate the effects of the driving frequency and acoustic power on the nucleation rate, efficiency, onset time, and dimensions of the nucleation region. The results showed that the inclusion of short pulsed high-frequency ultrasound significantly increased the nucleation rate with less energy, reduced the nucleation onset time, and changed the length-width ratio of the nucleation region, indicating the dual-frequency ultrasound mode yields an efficient enhancement of the ADV nucleation, compared to a single-frequency ultrasound mode. Furthermore, the acoustic and temperature fields varied independently with the dual-frequency ultrasound parameters. This facilitated the spatial and temporal control over the ADV nucleation, and opens the door to the possibility to realize on-demand regulation of the ADV occurrence in ultrasound theranostics. In addition, the improved energy efficacy that is obtained with the dual-frequency configuration lowered the requirements on hardware system, increasing its flexibility and could facilitate its implementation in practical applications.

High-Pressure Low-Frequency Lateral Mode Phased-Array Transducer System for the Treatment of Deep Vein Thrombosis: An In Vitro Study

Deep vein thrombosis (DVT) can lead to a fatal disease known as pulmonary embolism. Application of high-power ultrasound has been successful in studies to mechanically fragment the clots. Single-element ultrasound transducers were used in most of the studies. Challenges associated with phased arrays, such as high electrical impedance and element breakdown at high voltages, were addressed in the previous study, and a high-power 64-element transducer module was designed and fabricated. In this study, a cylindrical array of 16 modules with the frequency of 260 kHz was modeled and constructed for DVT thrombolysis. The maximum pressure, focal size, and steering ability of the array were examined. In vitro experiments were conducted to assess the performance of the array. The simulated pressure amplitude of 34 MPa at the depth of 55 mm (average femoral vein (FV) distance from the inner surface of the thigh) was in consistent with the experiments and satisfied the purpose of this study. Moreover, the employed module distribution resulted in a focal spot dimension of 2.4×2.8×7.3 mm³ (at the 75% pressure amplitude level) that can be confined in a human FV with the average diameter of 12 mm. In vitro experiments manifested a partial and complete clot breakdown at 11.5- and 15-MPa pressure at the focus. The design and engineering of the array system was succeeded in maintaining the desired pressure and focal size even when steered. The results presented in this study suggest the potential of the designed array system for clinical applications.

Ultrastructural Analysis of Volumetric Histotripsy Bio-effects in Large Human Hematomas

Large-volume soft tissue hematomas are a serious clinical problem, which, if untreated, can have severe consequences. Current treatments are associated with significant pain and discomfort. It has been reported that in an in vitro bovine hematoma model, pulsed high-intensity focused ultrasound (HIFU) ablation, termed histotripsy, can be used to rapidly and non-invasively liquefy the hematoma through localized bubble activity, enabling fine-needle aspiration. The goals of this study were to evaluate the efficiency and speed of volumetric histotripsy liquefaction using a large in vitro human hematoma model. Large human hematoma phantoms (85 cc) were formed by recalcifying blood anticoagulated with citrate phosphate dextrose/saline-adenine-glucose-mannitol solution. Typical boiling histotripsy pulses (10 or 2 ms) or hybrid histotripsy pulses using higher-amplitude and shorter pulses (0.4 ms) were delivered at 1% duty cycle while continuously translating the HIFU focus location. Histotripsy exposures were performed under ultrasound guidance with a 1.5-MHz transducer (8-cm aperture, F# = 0.75). The volume of liquefied lesions was determined by ultrasound imaging and gross inspection. Untreated hematoma samples and samples of the liquefied lesions aspirated using a fine needle were analyzed cytologically and ultrastructurally with scanning electron microscopy. All exposures resulted in uniform liquid-filled voids with sharp edges; liquefaction speed was higher for exposures with shorter pulses and higher shock amplitudes at the focus (up to 0.32, 0.68 and 2.62 mL/min for 10-, 2- and 0.4-ms pulses, respectively). Cytological and ultrastructural observations revealed completely homogenized blood cells and fibrin fragments in the lysate. Most of the fibrin fragments were less than 20 μm in length, but a number of fragments were up to 150 μm. The lysate with residual debris of that size would potentially be amenable to fine-needle aspiration without risk for needle clogging in clinical implementation.

Histotripsy: the first noninvasive, non-ionizing, non-thermal ablation technique based on ultrasound

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technology guided by real-time imaging. Using focused ultrasound delivered from outside the body, histotripsy mechanically destroys tissue through cavitation, rendering the target into acellular debris. The material in the histotripsy ablation zone is absorbed by the body within 1-2 months, leaving a minimal remnant scar. Histotripsy has also been shown to stimulate an immune response and induce abscopal effects in animal models, which may have positive implications for future cancer treatment. Histotripsy has been investigated for a wide range of applications in preclinical studies, including the treatment of cancer, neurological diseases, and cardiovascular diseases. Three human clinical trials have been undertaken using histotripsy for the treatment of benign prostatic hyperplasia, liver cancer, and calcified valve stenosis. This review provides a comprehensive overview of histotripsy covering the origin, mechanism, bioeffects, parameters, instruments, and the latest results on preclinical and human studies.