Evaluation of Ultrasonic Attenuation in Primary and Secondary Human Liver Tumors and Its Potential Effect on High-Intensity Focused Ultrasound Treatment

Enhancing Liver Nodule Visibility and Diagnostic Classification Using Ultrasound Local Attenuation Coefficient Slope Imaging

OBJECTIVE

B-mode ultrasound (US) presents challenges in accurately detecting and distinguishing between benign and malignant liver nodules. This study utilized quantitative US local attenuation coefficient slope (LACS) imaging to address these limitations.

MATERIALS AND METHODS

This is a prospective, cross-sectional study in adult patients with definable solid liver nodules at US conducted from March 2021 to December 2023. The composite reference standard included histopathology when available or magnetic resonance imaging. LACS images were obtained using a phantom-free method. Nodule visibility was assessed by computing the contrast-to-noise ratio (CNR). Classification accuracy for differentiating benign and malignant lesions was assessed with the area under the receiver operating characteristic curve (AUC), along with sensitivity and specificity.

RESULTS

The study enrolled 97 patients (age: 62 y ± 13 [standard deviation]), with 57.0% malignant and 43.0% benign observations (size: 26.3 ± 18.9 mm). LACS images demonstrated higher CNR (12.3 dB) compared to B-mode (p < 0.0001). The AUC for differentiating nodules and liver parenchyma was 0.85 (95% confidence interval [CI]: 0.79-0.90), with higher values for malignant (0.93, CI: 0.88-0.97) than benign nodules (0.76, CI: 0.66-0.87). A LACS threshold of 0.94 dB/cm/MHz provided a sensitivity of 0.83 (CI: 0.74-0.89) and a specificity of 0.82 (CI: 0.73-0.88). LACS mean values were higher (p < 0.0001) in malignant (1.28 ± 0.27 dB/cm/MHz) than benign nodules (0.98 ± 0.19 dB/cm/MHz).

CONCLUSION

LACS imaging improves nodule visibility and provides better differentiation between benign and malignant liver nodules, showing promise as a diagnostic tool.

The effect of temperature constraints on the treatment of tumors using focused ultrasound-induced acoustic streaming

The transport of drugs into tumor cells near the center of the tumor is known to be severely hindered due to the high interstitial pressure and poor vascularization. The aim of this work is to investigate the possibility to induce acoustic streaming in a tumor. Two tumor cases (breast and abdomen) are simulated to find the acoustic streaming and temperature rise, while varying the focused ultrasound transducer radius, frequency, and power for a constant duty cycle (1%). In the absence of perfusion, the simulated rise in temperature, despite the low duty cycle, never reaches a steady state and is fitted to a logarithmic equation, enabling predictions of the temperature for long treatment times. Higher frequencies and larger probe radii are found to result in shorter treatment times relative to the temperature rise, at the cost of a smaller treated area. Results from the simulations indicate that it may be possible to achieve reasonable acoustic streaming values in tumor without the temperature exceeding 50 °C. Treatment times for streaming a distance of 50 μm in the breast case are shown to range from less than one and a half hour to 93 h, depending on the probe settings.

High-intensity focused ultrasound treatment for hepatocellular carcinoma

High-intensity focused ultrasound (HIFU) represents a method employing high-intensity ultrasound energy to induce thermal ablation of cancerous cells. Regarded as minimally invasive, HIFU treatment offers reduced risk of complications and abbreviated recovery periods compared to surgical interventions. Although predominantly utilized in the management of pancreatic malignancies, ongoing investigations are exploring its viability in addressing hepatocellular carcinoma. Although HIFU may be employed independently in hepatocellular carcinoma treatment, its potential as a synergistic component within combination therapies is under scrutiny. Moreover, emerging research endeavors have explored the multifaceted utility of HIFU, encompassing not only localized thermal ablation but also functionalities like drug delivery and gene therapy, augmenting its therapeutic efficacy. Despite the promising outlook of HIFU in the management of hepatocellular carcinoma, existing constraints and challenges persist. Continued research initiatives and technological innovations are anticipated to propel HIFU into a pivotal and established therapeutic modality in the foreseeable future. This article provides an overview of HIFU therapy for hepatocellular carcinoma and presents a comprehensive update on its current clinical status.

Sound speed and attenuation of human pancreas and pancreatic tumors and their influence on focused ultrasound thermal and mechanical therapies

BACKGROUND

There is increasing interest in using ultrasound for thermal ablation, histotripsy, and thermal or cavitational enhancement of drug delivery for the treatment of pancreatic cancer. Ultrasonic and thermal modelling conducted as part of the treatment planning process requires acoustic property values for all constituent tissues, but the literature contains no data for the human pancreas.

PURPOSE

This study presents the first acoustic property measurements of human pancreatic samples and provides examples of how these properties impact a broad range of ultrasound therapies.

METHODS

Data were collected on human pancreatic tissue samples at physiological temperature from 23 consented patients in cooperation with a hospital pathology laboratory. Propagation of ultrasound over the 2.1-4.5 MHz frequency range through samples of various thicknesses and pathologies was measured using a set of custom-built ultrasonic calipers, with the data processed to estimate sound speed and attenuation. The results were used in acoustic and thermal simulations to illustrate the impacts on extracorporeal ultrasound therapies for mild hyperthermia, thermal ablation, and histotripsy implemented with a CE-marked clinical system operating at 0.96 MHz.

RESULTS

The mean sound speed and attenuation coefficient values for human samples were well below the range of values in the literature for non-human pancreata, while the human attenuation power law exponents were substantially higher. The simulated impacts on ultrasound mediated therapies for the pancreas indicated that when using the human data instead of the literature average, there was a 30% reduction in median temperature elevation in the treatment volume for mild hyperthermia and 43% smaller volume within a 60°C contour for thermal ablation, all driven by attenuation. By comparison, impacts on boiling and intrinsic threshold histotripsy were minor, with peak pressures changing by less than 15% (positive) and 1% (negative) as a consequence of the counteracting effects of attenuation and sound speed.

CONCLUSION

This study provides the most complete set of speed of sound and attenuation data available for the human pancreas, and it reiterates the importance of acoustic material properties in the planning and conduct of ultrasound-mediated procedures, particularly thermal therapies.

Ablation for malignant liver tumor using high-intensity focused ultrasound and radio-frequency: A meta-analysis

BACKGROUND

Primary liver cancer is a major health issue, so finding the most effective treatment is vital.

OBJECTIVE

The present meta-analysis compares high-intensity focused ultrasound (HIFU) to radiofrequency (RF) ablation for primary liver cancer treatment.

METHODS

PubMed, MEDLINE, CNKI, VIP, and Wanfang were used to search for English and Chinese papers. After carefully confirming data completeness and applying inclusion and exclusion criteria, RevMan 5.3 was used to evaluate the included literature. Data analysis utilized a fixed-effects model for heterogeneity between 0.1 and 0.5.

RESULTS

The meta-analysis included 304 patients: 119 had HIFU and 185 RF ablation. For primary liver cancer, HIFU and RF ablation were equally efficacious (odds ratio 1.02, 95% confidence interval [0.54, 1.92]). Overall survival, disease-free survival, and complications at 1, 2, and 3 years were not significantly different (odds ratio 0.72, 95% confidence range [0.04, 12.79], P= 0.82).

CONCLUSION

The meta-analysis shows no significant difference in efficacy, long-term survival rates, or complication rates between HIFU and RF ablation for primary liver cancer, but more large-scale, high-quality randomized clinical trials are needed to prove their equivalence. Both therapy strategies seem promising, but additional information is needed to determine their respective merits.

Non-invasive High-Intensity Focused Ultrasound Treatment of Liver Tissues in an In Vivo Porcine Model: Fast, Large and Safe Ablations Using a Toroidal Transducer

A toroidal high-intensity focused ultrasound (HIFU) transducer was used to non-invasively treat liver tissues in vivo in a pig model. The transducer was divided into 32 concentric rings with equal surface areas operating at 2.5 MHz. First, attenuation of skin, fat, muscle and liver tissues was measured in fresh animal samples to adjust the energy delivered to the focal zone. Then, 8 animals were included in the present protocol and placed in a dorsal decubitus proclive position at an angle of 15°. The device was held by hand, and sonications were performed during apnea. Two thermal HIFU lesions were created in 40 s in each animal. The average abdominal wall thickness was 14.8 ± 1.3 mm (12.5-17.6 mm). The longest and shortest axes of the HIFU ablations were 20.9 ± 6.3 mm (14.0-33.7 mm) and 14.2 ± 5.5 mm (7.0-22.0 mm), respectively. All HIFU lesions were visible on sonograms. The correlation between the dimensions of the HIFU lesions observed on sonograms and those obtained during gross examination was r = 0.84. Creating large and fast ablations with reliable ultrasound imaging guidance in the liver using this handheld device may represent a new therapeutic option for patients with liver tumors.

Effects of human tissue acoustic properties, abdominal wall shape, and respiratory motion on ultrasound-mediated hyperthermia for targeted drug delivery to pancreatic tumors

Background

PanDox is a Phase-1 trial of chemotherapeutic drug delivery to pancreatic tumors using ultrasound-mediated hyperthermia to release doxorubicin from thermally sensitive liposomes. This report describes trial-related hyperthermia simulations featuring: (i) new ultrasonic properties of human pancreatic tissues, (ii) abdomen deflections imposed by a water balloon, and (iii) respiration-driven organ motion.

Methods

Pancreas heating simulations were carried out using three patient body models. Pancreas acoustic properties were varied between values found in the literature and those determined from our human tissue study. Acoustic beam distortion was assessed with and without balloon-induced abdomen deformation. Target heating was assessed for static, normal respiratory, and jet-ventilation-controlled pancreas motion.

Results

Human pancreatic tumor attenuation is 63% of the literature values, so that pancreas treatments require commensurately higher input intensity to achieve adequate hyperthermia. Abdominal wall deformation decreased the peak field pressure by as much as 3.5 dB and refracted the focal spot by as much as 4.5 mm. These effects were thermally counteracted by sidelobe power deposition, so the net impact on achieving mild hyperthermia was small. Respiratory motion during moving beam hyperthermia produced localized regions overheated by more than 8.0 °C above the 4.0 °C volumetric goal. The use of jet ventilation reduced this excess to 0.7 °C and yielded temperature field uniformity that was nearly identical to having no respiratory motion.

Conclusion

Realistic modeling of the ultrasonic propagation environment is critical to achieving adequate mild hyperthermia without the use of real time thermometry for targeted drug delivery in pancreatic cancer patients.

Regularized Ultrasound Phantom-Free Local Attenuation Coefficient Slope (ACS) Imaging in Homogeneous and Heterogeneous Tissues

Attenuation maps or measurements based on the local attenuation coefficient slope (ACS) in quantitative ultrasound (QUS) have shown potential for the diagnosis of liver steatosis. In liver cancers, tissue abnormalities and tumors detected using ACS are also of interest to provide new image contrast to clinicians. Current phantom-based approaches have the limitation of assuming a comparable speed of sound between the reference phantom and insonified tissues. Moreover, these methods present the inconvenience for operators to acquire data on phantoms and patients. The main goal was to alleviate these drawbacks by proposing a methodology for constructing phantom-free regularized (PF-R) local ACS maps and investigate the performance in both homogeneous and heterogeneous media. The proposed method was tested on two tissue-mimicking media with different ACS constructed as homogeneous phantoms, side-by-side and top-to-bottom phantoms, and inclusion phantoms with different attenuations. Moreover, an in vivo proof-of-concept was performed on healthy, steatotic, and cancerous human liver datasets. Modifications brought to previous works include: 1) a linear interpolation of the power spectrum in the log scale; 2) the relaxation of the underlying hypothesis on the diffraction factor; 3) a generalization to nonhomogeneous local ACS; and 4) an adaptive restriction of frequencies to a more reliable range than the usable frequency range. Regularization was formulated as a generalized least absolute shrinkage and selection operator (LASSO), and a variant of the Bayesian information criterion (BIC) was applied to estimate the Lagrangian multiplier on the LASSO constraint. In addition, we evaluated the proposed algorithm when applying median filtering before and after regularization. Tests conducted showed that the PF-R yielded robust results in all tested conditions, suggesting potential for additional validation as a diagnosis method.

Prediction of programmed cell death protein 1 in hepatocellular carcinoma patients using radiomics analysis with radiofrequency-based ultrasound multifeature maps

BACKGROUND

This study explored the feasibility of radiofrequency (RF)-based radiomics analysis techniques for the preoperative prediction of programmed cell death protein 1 (PD-1) in patients with hepatocellular carcinoma (HCC).

METHODS

The RF-based radiomics analysis method used ultrasound multifeature maps calculated from the RF signals of HCC patients, including direct energy attenuation (DEA) feature map, skewness of spectrum difference (SSD) feature map, and noncentrality parameter S of the Rician distribution (NRD) feature map. From each of the above ultrasound maps, 345 high-throughput radiomics features were extracted. Then, the useful radiomics features were selected by the sparse representation method and input into support vector machine (SVM) classifier for PD-1 prediction.

RESULTS AND CONCLUSION

Among all the RF-based prediction models and the ultrasound grayscale comparative model, the RF-based model using all of the three ultrasound feature maps had the highest prediction accuracy (ACC) and area under the curve (AUC), which were 92.5% and 94.23%, respectively. The method proposed in this paper is effective for the meaningful feature extraction of RF signals and can effectively predict PD-1 in patients with HCC.