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Artigues-près-Bordeaux, France

Hey S.,Laboratory for Molecular and Functional Imaging | Cernicanu A.,Philips | de Senneville B.D.,Laboratory for Molecular and Functional Imaging | Roujol S.,Laboratory for Molecular and Functional Imaging | And 4 more authors.
NMR in Biomedicine | Year: 2012

Catheter ablation using radio frequency (RF) has been used increasingly for the treatment of cardiac arrhythmias and may be combined with proton resonance frequency shift (PRFS) -based MR thermometry to determine the therapy endpoint. We evaluated the suitability of two different MR thermometry sequences (TFE and TFE-EPI) and three blood suppression techniques. Experiments were performed without heating, using an optimized imaging protocol including navigator respiratory compensation, cardiac triggering, and image processing for the compensation of motion and susceptibility artefacts. Blood suppression performance and its effect on temperature stability were evaluated in the ventricular septum of eight healthy volunteers using multislice double inversion recovery (MDIR), motion sensitized driven equilibrium (MSDE), and inflow saturation by saturation slabs (IS). It was shown that blood suppression during MR thermometry improves the contrast-to-noise ratio (CNR), the robustness of the applied motion correction algorithm as well as the temperature stability. A gradient echo sequence accelerated by an EPI readout and parallel imaging (SENSE) and using inflow saturation blood suppression was shown to achieve the best results. Temperature stabilities of 2°C or better in the ventricular septum with a spatial resolution of 3.5×3.5×8mm 3 and a temporal resolution corresponding to the heart rate of the volunteer, were observed. Our results indicate that blood suppression improves the temperature stability when performing cardiac MR thermometry. The proposed MR thermometry protocol, which optimizes temperature stability in the ventricular septum, represents a step towards PRFS-based MR thermometry of the heart at 3T. © 2011 John Wiley & Sons, Ltd. Source

Hey S.,Laboratory for Molecular and Functional Imaging | De Senneville B.D.,Laboratory for Molecular and Functional Imaging | Maclair G.,Laboratory for Molecular and Functional Imaging | Mougenot C.,Philips | And 3 more authors.
AIP Conference Proceedings | Year: 2010

In this work, a method for the optimization of volumetric MR-guided high intensity focused ultrasound (HIFU) ablations is presented. We propose to monitor the thermal dose in the target area to ensure a complete destruction of the tumor tissue. A trajectory of ablation points is optimized based on the thermal energy distribution measured by PRFS-based MR thermometry. The combination with a 3D motion correction technique including tracking of the focal point position allows for an effective destruction of the target tissue with minimal energy, time and damage outside the target area. The proposed method was tested successfully in an ex-vivo experiment under conditions simulating respiratory movement of abdominal organs. © 2010 American Institute of Physics. Source

Enholm J.K.,Philips | Kohler M.O.,Philips | Quesson B.,Laboratory for Molecular and Functional Imaging | Mougenot C.,Laboratory for Molecular and Functional Imaging | And 2 more authors.
IEEE Transactions on Biomedical Engineering | Year: 2010

Volumetric high-intensity focused ultrasound (HIFU) guided by multiplane magnetic resonance (MR) thermometry has been shown to be a safe and efficient method to thermally ablate large tissue volumes. However, the induced temperature rise and thermal lesions show significant variability, depending on exposure parameters, such as power and timing, as well as unknown tissue parameters. In this study, a simple and robust feedback-control method that relies on rapid MR thermometry to control the HIFU exposure during heating is introduced. The binary feedback algorithm adjusts the durations of the concentric ablation circles within the target volume to reach an optimal temperature. The efficacy of the binary feedback control was evaluated by performing 90 ablations in vivo and comparing the results with simulations. Feedback control of the sonications improved the reproducibility of the induced lesion size. The standard deviation of the diameter was reduced by factors of 1.9, 7.2, 5.0, and 3.4 for 4-, 8-, 12-, and 16-mm lesions, respectively. Energy efficiency was also improved, as the binary feedback method required less energy to create the desired lesion. These results show that binary feedback improves the quality of volumetric ablation by consistently producing thermal lesions of expected size while reducing the required energy as well. © 2009 IEEE. Source

Mougenot C.,Philips | Mougenot C.,Laboratory for Molecular and Functional Imaging | Kohler M.O.,Philips | Enholm J.,Philips | And 2 more authors.
Medical Physics | Year: 2011

Purpose: High-intensity focused ultrasound guided by magnetic resonance imaging has been extensively evaluated during the past decade as a clinical alternative for thermal ablation of tumor tissue. However, the maximal ablation volume is limited by the extensive treatment duration resulting from the small size of the focal point as compared to the average tumor size. Volumetric sonication has been shown to efficiently enlarge the ablated volume per sonication, but remains limited by the temperature increase induced in the skin and fat layers. In this study, multiplane MR thermometry is proposed for monitoring the near-field temperature rise in order to prevent related unintended thermal damage. Methods: The method was evaluated by performing sonications in the thigh muscle of 11 pigs maintained under general anesthesia. Volumetric ablations were performed by steering the focal point along trajectories consisting of multiple outward-moving concentric circles. Near-field heating was characterized with MR temperature maps and thermal dose maps. The results from the MR measurements were compared to simulations. Results: In this study, the measured maximum temperature rise was found to correlate linearly with the surface energy density within the near field of the beam path with a slope of 4.2 K mm2/J. This simple linear model appears to be almost independent of the trajectory pattern and the sonication depth. The safety limit to avoid lethal damage of the subcutaneous tissues of the porcine thigh was identified to be an absolute temperature of 50 °C, corresponding to a surface energy density of 2.5 J/ mm2 at 1.2 MHz. Conclusions: A linear relationship can be established to estimate the temperature increase based on the chosen power prior to ablation, thereby providing an a priori safety check for possible excessive near-field heating using a known surface energy density threshold. This method would also give the clinician the possibility to abort the sonication should excessive near-field temperature rise be seen before fat layer damage or skin burns are inflicted. © 2011 American Association of Physicists in Medicine. Source

Mougenot C.,Philips | Mougenot C.,Laboratory for Molecular and Functional Imaging | Quesson B.,Laboratory for Molecular and Functional Imaging | Moonen C.,Laboratory for Molecular and Functional Imaging | Sokka S.,Philips
AIP Conference Proceedings | Year: 2011

This study proposes to increase the ablated volume by sequential MR-HIFU sonications exploiting the thermal diffusion of the previous sonications with a reduced cooling time between consecutive volumetric ablations. As result the use of an optimized sonication pattern provides an efficient (1.6ml/kJ) and a fast (4.6ml/min) ablation. © 2011 American Institute of Physics. Source

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