Biomedical subjects

David Melodelima

Publications and source records attributed to David Melodelima.

6 recordsLinked to original sources

PubMed2006

Elastography for breast cancer diagnosis using radiation force: system development and performance evaluation.

The use of impulsive acoustic radiation force for strain imaging was investigated. A focused ultrasound transducer was used to apply localized radiation force to a small volume of tissue mimic (100 mm3) for durations of 8 ms. A conventional real-time ultrasound imaging probe was used to obtain echo signals. The resulting strains were mapped using ultrasound correlation-based methods. The instantaneous strain immediately following cessation of the radiation force was observed at depth within homogeneous gels and within stiff inclusions, and was seen to vary approximately linearly with Young's modulus of the material. The highly localized and transient strain that is produced may permit the sensing of variations in tissue elastic properties that are difficult to detect with conventional elastography because of greater independence from boundary conditions. For example, the characteristic, bi-directional, high strain artefacts attributable to stress concentration, often seen with static elastography at tissue-inclusion interfaces, do not appear using the transient radiation force strain imaging technique.

Breast Neoplasms↗

PubMed2005

Intraluminal high intensity ultrasound treatment in the esophagus under fast MR temperature mapping: in vivo studies.

New curative and palliative treatments are needed to respond to the poor prognosis of esophageal cancer. The purpose of this study was to determine whether magnetic resonance imaging (MRI) and MR thermometry can be used to monitor the thermal ablation induced by an intraluminal high-intensity ultrasound applicator positioned in the esophagus. Experiments were performed in vivo in 2 pig esophagi (25 thermal lesions per pig). Respiratory gated or cardiac gated MR thermometry was performed with segmented echo-planar imaging gradient echo sequences. All MR acquisitions were performed without susceptibility artifacts or radiofrequency interference with the ultrasound device. The experimental procedure proposed for accurate measurement of temperature in the esophagus was found to achieve an SD of +/- 1.5 degrees C for respiratory gating and +/- 3.1 degrees C for cardiac gating. Gd-enhanced T(1)-weighted images were used to depict coagulation necrosis. Autopsy was performed immediately after the treatment. Ultrasound effects were inspected visually, and the dimensions of the lesions in the liver neighboring the esophagus were compared with those determined on the MRI images. The visually assessed thermal lesions showed good correlation with the MRI data (10% mean volume difference). The feasibility of esophageal thermal ablation using intraluminal high-intensity ultrasound and of on-line MR temperature monitoring was demonstrated.

Animals↗

PubMed2004

Comparison of two methods of treatment for intraluminal thermal ablation using an ultrasound cylindrical phased array.

Intraluminal (within the alimentary tract) thermal surgery has been shown to be a useful therapeutic option when extracorporeal focused ultrasound applicators cannot be used since their beam may not reach the target site. If plane transducers are used for the treatment of alimentary tract tumours, the applicator must be rotated in order to generate a cylindrical volume of necrosis. However, rotating these applicators and controlling their shooting direction presents technical difficulties. If tubular transducers are used it is difficult to treat arbitrary angles with a large therapeutic length. To solve these difficulties, the feasibility of an ultrasound phased array applicator has been evaluated using a cylindrical prototype (outer diameter 10.6 mm), which is composed of 16 elementary transducers working at 4.55 MHz and arranged on a quarter of the cylinder. Using this applicator it is possible to generate plane or cylindrical waves. Plane waves were generated by exciting eight successive elements of the array with appropriate delay times. The exposure direction was changed by exciting a different set of eight elements. In this way, the ultrasound beam was electronically rotated through the tissues. Cylindrical waves were generated by exciting several transducers without delay times. Imaging was provided using a miniature echographic probe. Ex vivo experiments were carried out in pig liver to compare two approaches of treatment. The first consisted of generating successive plane waves separated from each other by a 6 degrees angle. The second one consisted of exciting all the 16 elements without delay times. In the two cases, the lesions were well-defined and occupied a quarter of cylinder. In both sets of experiments, the sonication time and the intensity were 20 s and 17 W/cm(2), respectively. In the first case, the depth was up to 17 mm compared to 6 mm in the second case.

Animals↗

PubMed2004

Combination of thermal and cavitation effects to generate deep lesions with an endocavitary applicator using a plane transducer: ex vivo studies.

In the high-intensity focused ultrasound (US), or HIFU, field, it is well-known that the cavitation effect can be used to induce lesions of larger volume. The principle is based on the increase in the equivalent attenuation coefficient of the tissue in the presence of the bubbles created by cavitation. The elementary lesions produced by combination of cavitation and thermal effects, using focused transducers, were spherical and developed upstream of the focal point. This paper presents a method that combines cavitation with a thermal effect to obtain deeper lesions using a plane transducer, rather than a focused one. The cavitation effect was produced by delivering intensities of 60 W/cm2 at the face of the transducer for 0.5 s. The applicator was then rotated through 90 degrees at a constant speed of between 0.5 and 1.5 degrees /s. During this rotation, ex vivo tissues were exposed continuously to an acoustic intensity of 14 W/cm2 to combine the cavitation effect with a thermal effect. The necroses were, on average, twice as deep when the cavitation effect was used as those obtained with a thermal effect alone. Observed macroscopically, the lesions have a very well-delimited geometry. Temperature measurements made at different angles of treatment have shown that they were coagulation necroses.

Acoustics↗

PubMed2003

Transoesophageal ultrasound applicator for sector-based thermal ablation: first in vivo experiments.

New curative and palliative treatments must be proposed to respond to the bad long-term prognosis of oesophageal cancers. It has been demonstrated that high intensity ultrasound (US) can induce rapid, complete and well-defined coagulation necrosis. For the treatment of this cancer, we designed an applicator that uses an intraductal approach. The active part is an air-backed plane transducer. It has an external water-cooling system and operates at 10 MHz. Ex vivo experiments conducted on pig liver demonstrated the ability of this applicator to generate, by rotating the transducer, circular or sector-based coagulation necroses at predetermined depths up to 13 mm, with an excellent angular precision. The treatment of sector-based oesophageal tumours may be critical, where both malignant and healthy tissues are covered by the US beam. Thus, in vivo trials were conducted on five healthy pig oesophaguses to determine the maximal thermal dose that will not induce a perforation of the oesophagus or surrounding tissues. From the results of previous studies, this dose is high enough to treat pathological tissues. These promising results indicate that this US system represents a safe and effective tool for the clinical treatment of oesophageal tumours.

Animals↗

PubMed2002

Ultrasound cylindrical phased array for transoesophageal thermal therapy: initial studies.

This work was undertaken to investigate the feasibility of constructing a cylindrical phased array composed of 64 elements spread around the periphery (OD 10.6 mm) for transoesophageal ultrasound thermotherapy. The underlying operating principle of this applicator is to rotate a plane ultrasound beam electronically. For this purpose, eight adjacent transducers were successively excited with appropriate delay times so as to generate a plane wave. The exposure direction was changed by exciting a different set of eight elements. For these feasibility studies, we used a cylindrical prototype (OD 10.6 mm) composed of 16 elementary transducers distributed over a quarter of the cylinder, all operating at 4.55 MHz. The active part was mechanically reinforced by a rigid damper structure behind the transducers. It was shown that an ultrasound field similar to that emitted by a plane transducer could be generated. Ex vivo experiments on pig's liver demonstrated that the ultrasound beam could be accurately rotated to generate sector-based lesions to a suitable depth (up to 19 mm). Throughout these experiments, exposures lasting 20 s were delivered at an acoustic intensity of 17 W cm(-2). By varying the power from exposure to exposure, the depth of the lesion at different angles could be controlled.

Esophageal Neoplasms↗