W. A. N’Djin

Ultrasound surgery with a toric transducer allows the treatment of large volumes over short periods of time

Thermal ablation by physical agents is widely used in clinical settings, but it generally results in a small coagulated volume. Here, we report that a technologically advanced high intensity focused ultrasound transducer can significantly enlarge the coagulated volume over short periods of time. Eight ultrasound emitters were created by sectioning a single toric piezocomposite transducer. A single thermal lesion is created when the eight emitters perform alternative and consecutive 5s ultrasound exposures. This paper presents in vivo evidence that the coagulated volume obtained from a 40s total exposure in the liver was 8.6±4.8cm3.

Modèle de pseudotumeur pour guider l’ablation thermique par ultrasons focalisés : étude sur le porc

Resume Il n’existe pas de modele tumoral chez le porc pour etudier les effets des traitements localises par agents physiques des tumeurs du foie. Un modele de pseudotumeur reperable en echographie et macroscopiquement a ete etudie sur 20 porcs a moyen terme pour valider les etudes de therapie par ultrasons focalises au stade preclinique. Les pseudotumeurs ont des dimensions echographiques reproductibles (diametre : 9,6 ± 1,9 mm) et correlees a la mesure sur la piece operatoire (R 2 = 0,73). Une etude de ciblage de la therapie ultrasonore montre que ce modele permet de verifier si la destruction tissulaire observee sur la piece operatoire correspond a la zone ciblee sur l’image echographique.

In‐vivo ablation of liver tumors by high‐intensity‐focused ultrasound using a toroidal transducer. Results of animal experiments

The aim of this study was to demonstrate in a rabbit liver tumor model that high intensity focused ultrasound (HIFU) produced with toroidal‐shaped emitters may have a role in treating colorectal liver metastases. The HIFU device was composed of eight ultrasound emitters created by sectioning a single toroidal piezocomposite transducer. Each of the eight emitters was divided into 32 transducers operating at a frequency of 3 MHz. The toroidal transducer has a diameter of 70 mm and a radius of curvature of 70 mm. A 7.5 MHz ultrasound imaging probe (Vermon, Tours, France) was placed in the centre of the device. Using this transducer, single lesions of 7 cm3 were created in 40 seconds. Juxtaposition of single lesions was performed under ultrasound guidance. VX2 tumor segments (25 mg) were implanted into right lateral liver lobes of 45 New Zealand white rabbits. Fifteen rabbits were treated with toroidal HIFU ablation (Group 1). Fifteen rabbits were resected (Group 2). Fifteen rabbits were not treated and forme...

Preclinical Evaluation of the Accuracy of HIFU Treatments Using a Tumor‐Mimic Model. Results of Animal Experiments

Presented in this paper is a tumor‐mimic model that allows the evaluation at a preclinical stage of the targeting accuracy of HIFU treatments in the liver. The tumor‐mimics were made by injecting a warm mixture of agarose, cellulose, and glycerol that polymerizes immediately in hepatic tissue and forms a 1 cm discrete lesion that is detectable by ultrasound imaging and gross pathology. Three studies were conducted: (i) in vitro experiments were conducted to study acoustical proprieties of the tumor‐mimics, (ii) animal experiments were conducted in ten pigs to evaluate the tolerance of the tumor‐mimics at mid‐term (30 days), (iii) ultrasound‐guided HIFU ablation has been performed in ten pigs with tumor‐mimics to demonstrate that it is possible to treat a predetermined zone accurately. The attenuation of tumor‐mimics was 0.39 dB.cm‐1 at 1 MHz, the ultrasound propagation velocity was 1523 m.s‐1, and the acoustic impedance was 1.8 MRayls. The pigs tolerated tumor‐mimics and treatment well over the experiment...

Impact of Real Liver Motion on HIFU Treatments: an in‐vivo‐data‐based modeling

Organs motion is a key component in the treatment of abdominal lesions by HIFU, since it may influence the efficacy and treatment time. Previous studies on HIFU treatments showed the effect of motor‐controlled translations applied to in vitro liver samples. In vivo organs motions are more complex and could lead to various effects on HIFU treatments. Here we report that a combined method can be used for simulating the effect of real in vivo motion on HIFU lesion in the liver. Sequences of ultrasound images were acquired in vivo during an open procedure on 4 pigs during breathing and apnea using a 12 MHz ultrasound imaging probe. Ultrasound correlation‐based methods were used to estimate liver motion using speckle tracking. These in vivo motion data were included in numerical simulations based on Bio Heat Transfer Equation for evaluating the influence of motion on treatments performed with a 3 MHz spherical HIFU transducer. Data acquired during breathing confirmed that liver motions were mainly encountered ...

1D multi-element CMUT arrays for ultrasound thermal therapy

Interstitial therapeutic ultrasound devices are a promising technology for performing thermal ablation in a wide variety of organs. In this study, the use of Capacitive Micromachined Ultrasound Transducers (CMUTs) for interstitial heating applications was investigated. CMUTs exhibit potential advantages for use in therapeutic ultrasound applications in comparison to standard piezo ultrasound transducer technologies as they have good characteristics in terms of miniaturization (cell size: few dozens of microns), bandwidth (several MHz) and high electro-acoustic efficiency. Two designs of CMUT arrays were studied: (1) a 1D 128-element planar-CMUT array originally dedicated to abdominal ultrasound imaging purposes (5 MHz, element size: 0.3 × 8.0 mm2); (2) a 12-element linear-array, 32.4-mm long and 0.8-mm wide, developed specifically for minimally-invasive interstitial therapeutic applications (6 MHz, element size: 2.7 × 0.8 mm2). Simulations were performed to evaluate the ability to generate thermal lesions...

Segmental liver resection assisted by HIFU: tissue precauterization using a toroidal‐shaped HIFU transducer

The development of new cauterization techniques for hepatic resection is critical for improving the safety of the procedure. Previous studies showed the feasibility of using HIFU or radiofrequency precoagulation to limit blood loss during dissection of the organ. Here we report a new therapeutic modality using high intensity focused ultrasound (HIFU) to perform a bloodless hepatic resection that could represent a promising alternative. A comparative study was performed to evaluate the interest of using this complementary tool to improve surgical resection in the liver. This study used a 3 MHz HIFU toroidal‐shaped phased array transducer which allows the generation of a single conical lesion of 7 cm3 in 40 seconds. In order to minimize blood loss and dissection time, a barrier of coagulative necrosis was generated with the HIFU device before hepatectomy, by juxtaposing single conical lesions on the line of dissection. Resection assisted by HIFU (RA‐HIFU) was compared with classical dissections with clampin...

Effects of respiratory motion on in‐vivo HIFU treatments: a comparative study in the liver

Current development of HIFU strategies for the treatment of localized abdominal tumors are limited by organ motion during respiration. In preliminary studies, a numerical model simulated the effects of in‐vivo movements on HIFU treatments in the liver. It was shown that a HIFU treatment performed during respiration with juxtaposition of millimetrics lesions is modified in shape and homogeneity. Here, we report recent results from a comparative study which evaluated in simulation and in in‐vivo experiments, the interest of using, during respiratory, a toroidal‐shaped HIFU device developed for the treatment of Liver Metastases from Colorectal Cancer. These experiments were performed during an open procedure, on 9 pigs divided into 3 groups. On the first group, a spherical HIFU transducer was used to juxtapose 49 millimetrics lesions in the liver during respiration. The second group was treated during respiration with a 3 MHz toroidal‐shaped HIFU transducer. The last group (control) was treated during apnea....

A toroidial‐shaped HIFU transducer for assisting hepatic resection: a complementary tool for surgery

A toroidial‐shaped HIFU medical device with integrated ultrasound imaging was developed for the treatment of colorectal liver metastasis. The HIFU toroidial‐shaped transducer contained 256‐elements (working frequency: 3 MHz) and allows creating a single conical lesion of 7 cm3 in 40 seconds (Ifocal = 1700 W.cm−2). Volumes of treatment can then be significantly increase by juxtaposing single lesions. Presented here is the use of this device in an animal model as a complementary tool to improve surgical resection in the liver. A zone of coagulative necrosis before transecting the liver was performed using this device in order to minimize blood loss and dissection time during hepatectomy. Resection assisted by HIFU (RA‐HIFU) was compared with classical dissections with clamping (RC) and without clamping (Control). For each technique 14 partial liver resections were performed in seven pigs. Blood loss per dissection surface area was the main outcome parameter. Blood loss during liver transection was significa...

Thermal Ablation by High-Intensity-Focused Ultrasound Using a Toroid Transducer Increases the Coagulated Volume and Allows Coagulation Near Portal and Hepatic veins in Pigs

A new geometry of HIFU transducer is described to enlarge the coagulated volume. The geometry of the transducer was not spherical. The surface of the transducer was built based on a toroid geometry. The transducer was generated by the revolution of a circle about an axis lying in its plane. Eight emitters operating at a frequency of 3 MHz were diced out of a single toroid piezocomposite element. Each of the eight emitters was divided into 32 transducers. The focal zone is conical and located at 70 mm from the transducer. A 7.5 MHz ultrasound imaging probe is placed in the centre of the device for guiding the treatment. Our long‐term objective is to develop a device that can be used during surgery. In vivo trials have been performed on 13 pigs to demonstrate this new principle and to evaluate the vascular tolerance of the treatment. This new geometry combined with consecutive activation of the eight emitters around the toroid allows achieving a mean thermal ablation of 7.0±2.5 cm3 in 40 seconds. All lesion...