Non-invasive high-intensity focused ultrasound treatment of the placenta: a preliminary in-vivo study using a simian model

Experimental Evaluation of an Ultrasound-Guided High-Intensity-Focused Ultrasound Probe for Sonication of Artery

OBJECTIVES

This study aimed to develop an ultrasound-guided high-intensity-focused ultrasound (USgHIFU) probe for arterial sonication and to evaluate vascular contraction.

METHODS

The USgHIFU probe comprised two confocal spherical transducers for sonication and a US color Doppler flow imaging probe for guidance. A vessel-mimicking phantom was sonicated in two directions. In the vascular radial direction, an isolated rabbit aorta embedded in ex vivo pork liver was sonicated at different acoustic powers (245 and 519 W), flow rates (25, 30, and 50 mL/minute), and sonication energies (519, 980, and 1038 J). Changes in the postsonication vessels were evaluated using US imaging, microscopic observation, and histopathological analysis.

RESULTS

Beam focusing along the vascular radial direction caused significant deformation of both tube walls (n = 4), whereas focusing along the axial direction only affected the contraction of the anterior wall (n = 4). The contraction index (Dc) of the vessel sonicated at 245 W and 980 J was 56.2 ± 9.7% (n = 12) with 25 mL/minute. The Dc of the vessel sonicated at 519 W and 1038 J was 56.5 ± 7.8% (n = 17). The Dc of the vessel sonicated at 519 J total energy was 18.3 ± 5.1% (n = 12).

CONCLUSION

The developed USgHIFU probe induced greater vascular contractions by covering a larger area of the vessel wall in the radial direction. Sonication energy affects vascular contraction through temperature elevation of the vessel wall. When the acoustic power was high, an increase in acoustic power, even with comparable sonication energy, did not result in greater vessel contraction.

Clinical value of high-intensity focused ultrasound in fetal reduction

Complex twin reduction surgery is a common but challenging procedure that aims to reduce the risks and complications of multiple pregnancies. The search for safer and more effective methods has led to the development of high-intensity focused ultrasound (HIFU) technology in the field of fetal reduction. This technology utilizes high-energy sound waves to focus precisely on specific areas, achieving non-invasive therapeutic effects. This paper discusses the principles and features of HIFU technology, as well as its application in complex twin reduction surgery. The paper aims to elucidate the important role of this technology in improving surgical outcomes and reducing risks, explore the current limitations of the modality, and propose directions for future development. Through these investigations, it is hoped to improve overall understanding of HIFU, and thereby promote the application of this technology in the field of fetal reduction.

In vivo exposure of the bladder using a non-invasive high intensity focused ultrasound toroidal transducer

A toroidal high-intensity focused ultrasound (HIFU) transducer was used to expose normal bladder wall tissues non-invasively in vivo in a porcine model in order to investigate the potential to treat bladder tumors. The transducer was divided into 32 concentric rings with equal surface areas, operating at 2.5 MHz. Eight animals were split into two groups of 4. In the first group, post-mortem evaluation was performed immediately after ultrasound exposure. In the second group, animals survived for up to seven days before post-mortem evaluation. The ultrasound imaging guided HIFU device was hand-held during the procedure using optical tracking to ensure correct targeting. One thermal lesion in each animal was created using a 40 s exposure at 80 acoustic Watts (free-field) in the trigone region of the bladder wall. The average (±Standard Deviation) abdominal wall and bladder wall thicknesses were 10.3 ± 1.4 mm and 1.1 ± 0.4 mm respectively. The longest and shortest axes of the HIFU ablations were 7.7 ± 2.9 mm and 6.0 ± 1.8 mm, respectively, resulting in an ablation of the whole thickness of the bladder wall in most cases. Ablation were performed at an average depth (distance from the skin surface to the centre of the HIFU lesion) of 42.5 ± 3.8 mm and extended throughout the thickness of the bladder. There were two cases of injury to tissues immediately adjacent to the bladder wall but without signs of perforation, as confirmed by histological analysis. Non-invasive HIFU ablation using a hand-held toroidal transducer was successfully performed to destroy regions of the bladder wall in vivo.

High-intensity focused ultrasound for noninvasive fetal therapy

High-intensity focused ultrasound (HIFU) consists of an ultrasonic beam that is focused within the body to induce tissue necrosis through both heat energy and as a result of cavitation, which occurs without damaging any intervening tissues. Therefore, it is possible to cauterize and treat tumors without surgical invasion by administering HIFU irradiation from outside the body. This approach has been clinically applied in various fields in recent years, and fetal therapy is no exception, with several clinical applications reported, mainly in basic experiments. This review summarizes the recent basic and clinical findings focusing on fetal treatment with HIFU.

Retrospective validation of 11-13 weeks' gestation ultrasound characteristics as predictive tools for twin-twin transfusion syndrome and selective intrauterine growth restriction in monochorionic diamniotic twin pregnancies

Background

Twin to twin transfusion syndrome (TTTS) is a serious syndrome that can affect twin pregnancies involving a single placenta, impacts some of twin gestations with monochorionic diamniotic (MCDA) placentas. We validated the ultrasound characteristics of 11–13 weeks’ gestation to predict TTTS and selective intrauterine growth restriction (sIUGR) in MCDA pregnancies.

Methods

We retrospectively included all of the MCDA twin pregnancies with ultrasound characteristics, including the crown-rump length (CRL), ductus venosus pulsatility index for veins (DV PIV), and nuchal translucency (NT) thickness, at 11–13 weeks’ gestation, followed by mean difference and discordance comparison. Receiver operating characteristic (ROC) curves were constructed for the comparison of values of these predictive markers for identification of MCDA pregnancies with high-risk of adverse outcomes.

Results

A total of 98 MCDA pregnancies were included in this study. Among the 98, 34 (34.7%) developed sIUGR, whereas 10 (10.2%) expressed TTTS. Significant differences in NT discordance were found among the normal, sIUGR, and TTTS groups; moreover, a significant difference was found between pregnancies with normal outcomes and sIUGR (P<0.001), normal and TTTS (P<0.001), and sIUGR and TTTS (P<0.001). Difference in NT was determined to be the best predictive marker for sIUGR [area under the curve (AUC) =0.769; 95% confidence interval (CI): 0.591 to 0.992], and NT discordance was considered the best predictive marker for TTTS (AUC =0.802; 95% CI: 0.485 to 0.936).

Conclusions

Significant differences in NT discordance were found between the normal, sIUGR, and TTTS groups, while NT difference and NT discordance were identified as predictive markers for sIUGR and TTTS, respectively.

Development of a noninvasive HIFU treatment for breast adenocarcinomas using a toroidal transducer based on preliminary attenuation measurements

Breast cancer is the most commonly diagnosed type of cancer among women. For the last fifteen years, treatments that are less invasive than lumpectomy, such as high-intensity focused ultrasound (HIFU) therapy, have been developed, with encouraging results. In this study, a toroidal HIFU transducer was used to create lesions of at least 2 cm in diameter within less than one minute of treatment. The toroidal HIFU transducer created two focal zones that led to large, fast and homogeneous ablations (10.5 cc/min). The experiments were conducted in 30 human samples of normal breast tissues recovered from mastectomies to measure acoustic attenuation (N = 30), and then, HIFU lesions were created (N = 15). Eight HIFU ablations were performed to evaluate the reproducibility of the lesions. HIFU lesions were created in 45 s with a toroidal HIFU transducer working at 2.5 MHz. The longest and shortest axes of the HIFU lesions were 21.7 ± 3.1 mm and 23.5 ± 3.3 mm respectively, corresponding to an average volume of 7.3 ± 1.4 cm³. These HIFU lesions were performed at an average depth of 19.0 ± 1.5 mm, while the integrity of the skin was preserved. The HIFU-treated breast tissues had a higher level of attenuation (0.57 ± 0.11 Np.cm^-1.MHz^-1) when compared to the untreated tissues (0.21 ± 0.04 Np.cm^-1.MHz^-1). This study shows the feasibility of a fast and fully noninvasive treatment using a toroidal transducer for breast tumors measuring up to 15 mm in diameter.

Fast and Selective Ablation of Liver Tumors by High-Intensity Focused Ultrasound Using a Toroidal Transducer Guided by Ultrasound Imaging: The Results of Animal Experiments

This study demonstrated that high-intensity focused ultrasound (HIFU) produced with an intra-operative toroidal-shaped transducer causes fast, selective liver tumor ablations in an animal model. The HIFU device is composed of 256 emitters working at 3 MHz. A 7.5 MHz ultrasound imaging probe centered on the HIFU transducer guided treatment. VX2 tumor segments (25 mg) were implanted into the right lateral liver lobes of 45 New Zealand rabbits. The animals were evenly divided into groups 1 (toroidal HIFU ablation), 2 (surgical resection) and 3 (untreated control). Therapeutic responses were evaluated with gross pathology and histology 11 d post-treatment. Toroidal transducer-produced HIFU ablation (average ablation rate 10.5 cc/min) allowed fast and homogeneous tumor treatment. Sonograms showed all ablations. VX2 tumors were completely coagulated and surrounded by safety margins without surrounding-organ secondary HIFU lesions. HIFU group tumor volumes at autopsy (39 mm³) were significantly lower than control group volumes (2610 mm³, p < 0.0001). HIFU group tumor metastasis (27%) was lower than resected (33%) and control (67%) group metastasis. Ultrasound imaging, gross pathology and histology results supported these outcomes. HIFU procedures had no complications. Rabbit liver tumor ablation using a toroidal HIFU transducer under ultrasound imaging guidance might therefore be an effective intra-operative treatment for localized liver metastases.

Non-invasive dynamic observation of placental vascular anastomoses in monochorionic twins: Assessment using three-dimensional sonography combined with tomographic ultrasound imaging

INTRODUCTION

Three-dimensional (3D) sonography combined with tomographic ultrasound imaging (TUI) to observe placental vascular anastomoses in monochorionic diamniotic (MCDA) twin pregnancies was evaluated.

METHODS

Women with MCDA twin pregnancies at a gestational age of 16-32 weeks were enrolled in this retrospective study. Placental anastomoses were detected using two-dimensional (2D) and 3D sonography. Two-dimensional data were obtained by color and spectral Doppler and 3D data with high-definition flow within the area between twins' umbilical cord insertions. Volume post-processing using TUI mode identified anastomoses. Anastomotic findings on ultrasound were compared with fetoscopic surgery or postnatally injected placentas for diagnostic value. Anastomoses detection was compared between the two imaging modalities.

RESULTS

Seventy-six twin pregnancies were analyzed: 11 selective intrauterine growth restrictions (sIUGR), 10 twin-to-twin transfusion syndrome (TTTS), and 55 without complications. Seventy-one twin pregnancies had arterio-arterial (AA) anastomoses and 75 had arterio-venous (AV) anastomoses. Three-dimensional sonography combined with TUI was more sensitive (87.3%) and accurate (88.2%) in detecting AA anastomoses than 2D sonography (74.6%, 76.3%, respectively; P < 0.05), but had comparable sensitivity for AV anastomoses. The specificity of both modalities for anastomoses was 100%. The detection rate of AA anastomoses by 3D modality was (40%) TTTS vs. (87.3%) normal (P < 0.05), but comparable (90.9%) for sIUGR. The detection rates of AV anastomoses (90%, 81.8%) in TTTS and sIUGR were comparable with (87.3%) normal (P > 0.05).

DISCUSSION

Three-dimensional sonography combined with TUI highlighted placental anastomoses and may be useful for the clinical diagnosis and therapy of MCDA twin complications.

Prospective Validation of First-Trimester Ultrasound Characteristics as Predictive Tools for Twin-Twin Transfusion Syndrome and Selective Intrauterine Growth Restriction in Monochorionic Diamniotic Twin Pregnancies

OBJECTIVE

Monochorionic diamniotic (MCDA) twins are at increased risk of adverse outcome due to unequal placental sharing and placental vascular communications between the fetal circulations. Most centres perform ultrasound examination every 2-3 weeks to identify these complications. Identifying a high-risk cohort of MCDA twins in the first trimester would allow more efficient surveillance. We have attempted to validate first-trimester ultrasound characteristics as predictive tools for twin-twin transfusion syndrome (TTTS) and selective intrauterine growth restriction (sIUGR) in MCDA twins.

MATERIAL AND METHODS

This is a prospective cohort study including MCDA twins enrolled at the time of first-trimester combined screening. Differences in crown-rump length (CRL), nuchal translucency (NT) thickness, ductus venosus pulsatility index for veins (DV PIV), presence or absence of tricuspid regurgitation and right ventricular E/A ratio were assessed. Receiver operating characteristic (ROC) curves were used to assess the potential value of these measures as predictive tools for identifying a cohort of MCDA pregnancies at high risk of adverse pregnancy outcome.

RESULTS

Sixty-five MCDA pregnancies were included in the analysis. Nine (14%) developed TTTS, 17 (26%) developed sIUGR. The best predictive marker for TTTS was NT discordance of ≥20% (ROC AUC = 0.79; 95% CI 0.59-0.99). Combining measures did not improve performance (AUC = 0.80; 95% CI 0.62-0.99).

CONCLUSION

NT discordance was the most effective characteristic at predicting TTTS but still had a relatively poor positive predictive value (36%). Intertwin differences in CRL, DV PIV and E/A ratio were not predictive of subsequent pregnancy complications. None of these characteristics have sufficient efficacy to be used to triage MCDA twin pregnancies ongoing obstetric surveillance.

Noninvasive ablation of rabbit fetal and placental tissue targets in utero using magnetic resonance-guided high-intensity focused ultrasound

OBJECTIVE

Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) is a potential noninvasive therapy for fetal conditions. In utero MRgHIFU delivery and proton resonance frequency shift (PRFS) thermometry monitoring will control accuracy of HIFU ablation and confirm in situ tissue heating in a rabbit model.

METHODS

High-resolution 3T MR images were acquired in late-gestation rabbits (approximately 30 days, n = 5). HIFU sonications, using magnetic resonance (MR) thermometry as a guide, were delivered to achieve necrosis in relevant fetal targets. Thermometry, posttreatment magnetic resonance imaging (MRI), and follow-up histology confirmed ablation.

RESULTS

Placentas (n = 14) were treated with 127 ± 34 Wac; thermometry-indicated temperatures reached 67°C. Lungs (n = 8) were treated with 85 ± 15 Wac and reached 73°C, livers (n = 6) with 80 ± 15 Wac and reached 74°C, and kidneys (n = 5) with 100 Wac and reached 66°C. Histological changes showed focal areas of necrosis with circumferential hemorrhage and/or vasodilation, which transitioned abruptly to healthy tissue.

CONCLUSION

MRgHIFU therapy can effectively target and thermally treat specific in utero organs in this acute fetal rabbit model. PRFS gives in situ temperature control of therapy on tissues. Conceivably, MRgHIFU therapy may be applicable to specific fetal organ anomalies clinically and has the potential to improve the overall fetal outcome over traditional invasive surgical procedures.