Aberration correction in abdominal histotripsy

Evaluation of targeting accuracy of cone beam CT guided histotripsy in an in vivo porcine model

PURPOSE

The application of histotripsy, an emerging noninvasive, non-ionizing, and non-thermal tumor treatment, is currently limited by the inherent limitations of diagnostic ultrasound as the sole targeting modality. This study evaluates the feasibility and accuracy of cone beam computed tomography (CBCT) guidance for histotripsy treatments in an in vivo porcine model.

MATERIALS AND METHODS

Histotripsy treatments were performed in the liver of seven healthy swine under the guidance of a C-arm CBCT system that was calibrated to the robotic arm of the histotripsy system. For each treatment, pseudotumors (small histotripsy treatments of 15 mm) were created using conventional US guidance to serve as targets for subsequent CBCT guided treatments. A pretreatment CBCT with intravenous contrast was acquired for each swine and the center of the pseudotumor was selected as the target. The robotic arm automatically aligned the transducer to the selected target location. Ultrasound based aberration offset correction was performed when possible, and a 25 mm diameter treatment was performed. A post-treatment CBCT with intravenous contrast was then acquired to evaluate coverage, treatment size, and distance between the pseudotumor target and actual treatment zone center.

RESULTS

Treatments were technically successful and pseudotumors were completely covered in all seven treatments (7/7). The average treatment diameter was 39.3 ± 4.2 mm. The center-to-center distance between pseudotumor and actual treatments was 3.8 ± 1.3 mm.

CONCLUSION

CBCT provides accurate targeting for histotripsy treatment in vivo. While future work is required to assess safety and efficacy in the presence of obstructions, the proposed approach could supplement ultrasound imaging for targeting.

Overview of Therapeutic Ultrasound Applications and Safety Considerations: 2024 Update

A 2012 review of therapeutic ultrasound was published to educate researchers and physicians on potential applications and concerns for unintended bioeffects (doi: 10.7863/jum.2012.31.4.623). This review serves as an update to the parent article, highlighting advances in therapeutic ultrasound over the past 12 years. In addition to general mechanisms for bioeffects produced by therapeutic ultrasound, current applications, and the pre-clinical and clinical stages are outlined. An overview is provided for image guidance methods to monitor and assess treatment progress. Finally, other topics relevant for the translation of therapeutic ultrasound are discussed, including computational modeling, tissue-mimicking phantoms, and quality assurance protocols.

Neutrophil extracellular traps in tumor progression of gynecologic cancers

This article delves into the intricate interplay between tumors, particularly gynecologic malignancies, and neutrophil extracellular traps (NETs). The relationship between tumors, specifically gynecologic malignancies, and NETs is a multifaceted and pivotal area of study. Neutrophils, pivotal components of the immune system, are tasked with combating foreign invaders. NETs, intricate structures released by neutrophils, play a vital role in combating systemic infections but also play a role in non-infectious conditions such as inflammation, autoimmune diseases, and cancer. Cancer cells have the ability to attract neutrophils, creating tumor-associated neutrophils, which then stimulate the release of NETs into the tumor microenvironment. The impact of NETs within the tumor microenvironment is profound and intricate. They play a significant role in influencing cancer development and metastasis, as well as modulating tumor immune responses. Through the release of proteases and pro-inflammatory cytokines, NETs directly alter the behavior of tumor cells, increasing invasiveness and metastatic potential. Additionally, NETs can trigger epithelial-mesenchymal transition in tumor cells, a process associated with increased invasion and metastasis. The interaction between tumors and NETs is particularly critical in gynecologic malignancies such as ovarian, cervical, and endometrial cancer. Understanding the mechanisms through which NETs operate in these tumors can offer valuable insights for the development of targeted therapeutic interventions. Researchers are actively working towards harnessing this interaction to impede tumor progression and metastasis, opening up new avenues for future treatment modalities. As our understanding of the interplay between tumors and NETs deepens, it is anticipated that novel treatment strategies will emerge, potentially leading to improved outcomes for patients with gynecologic malignancies. This article provides a comprehensive overview of the latest research findings on the interaction between NETs and cancer, particularly in gynecologic tumors, serving as a valuable resource for future exploration in this field.

In Vivo Cavitation-Based Aberration Correction of Histotripsy in Porcine Liver

Histotripsy is a noninvasive ablation technique that focuses ultrasound pulses into the body to destroy tissues via cavitation. Heterogeneous acoustic paths through tissue introduce phase errors that distort and weaken the focus, requiring additional power output from the histotripsy transducer to perform therapy. This effect, termed phase aberration, limits the safety and efficacy of histotripsy ablation. It has been shown in vitro that the phase errors from aberration can be corrected by receiving the acoustic signals emitted by cavitation. For transabdominal histotripsy in vivo, however, cavitation-based aberration correction (AC) is complicated by acoustic signal clutter and respiratory motion. This study develops a method that enables robust, effective cavitation-based AC in vivo and evaluates its efficacy in the swine liver. The method begins with a high-speed pulsing procedure to minimize the effects of respiratory motion. Then, an optimal phase correction is obtained in the presence of acoustic clutter by filtering with the singular value decomposition (SVD). This AC method reduced the power required to generate cavitation in the liver by 26% on average (range: 0%-52%) and required ~2 s for signal acquisition and processing per focus location. These results suggest that the cavitation-based method could enable fast and effective AC for transabdominal histotripsy.

A target containing phantom for accuracy assessment of cone-beam CT-guided histotripsy

PURPOSE

Histotripsy is a nonionizing, noninvasive, and nonthermal focal tumor therapy. Cone-beam computed tomography (CBCT) guidance was developed for targeting tumors not visible on ultrasound. This approach assumes cavitation is formed at the geometrical focal point of the therapy transducer. In practice, the exact location might vary slightly between transducers. In this study, we present a phantom with an embedded target to evaluate CBCT-guided histotripsy accuracy and assess the completeness of treatments.

METHODS

Spherical (2.8 cm) targets with alternating layers of agar and radiopaque barium were embedded in larger phantoms with similar layers. The layer geometry was designed so that targets were visible on pre-treatment CBCT scans. The actual histotripsy treatment zone was visualized via the mixing of adjacent barium and agar layers in post-treatment CBCT images. CBCT-guided histotripsy treatments of the targets were performed in six phantoms. Offsets between planned and actual treatment zones were measured and used for calibration refinement. To measure targeting accuracy after calibration refinement, six additional phantoms were treated. In a separate investigation, two groups (N = 3) of phantoms were treated to assess visualization of incomplete treatments ("undertreatment" group: 2 cm treatment within 2.8 cm tumor, "mistarget" group: 2.8 cm treatment intentionally shifted laterally). Treatment zones were segmented (3D Slicer 5.0.3), and the centroid distance between the prescribed target and actual treatment zones was quantified.

RESULTS

In the calibration refinement group, a 2 mm offset in the direction of ultrasound propagation (Z) was measured. After calibration refinement, the centroid-to-centroid distance between prescribed and actual treatment volumes was 0.5 ± 0.2 mm. Average difference between the prescribed and measured treatment sizes in the incomplete treatment groups was 0.5 ± 0.7 mm. In the mistarget group, the distance between prescribed and measured shifts was 0.2 ± 0.1 mm.

CONCLUSION

The proposed prototype phantom allowed for accurate measurement of treatment size and location, and the CBCT visible target provided a simple way to detect misalignments for preliminary quality assurance of CBCT-guided histotripsy.