Development of MRI methods for guidance of focused ultrasound treatment of pancreatic tumors

MR guided High Intensity Focused Ultrasound (MR-HIFU) is a promising non-invasive therapeutic modality. It makes use of ultrasound waves to cause localized heating of a target volume, e.g. a tumor, deep inside the patient’s body. MRI is used to plan, monitor and evaluate the treatment procedure, by means of high-resolution imaging and MR thermometry techniques that allow real-time temperature mapping. Currently, pancreatic cancer patients have a poor prognosis. While MR-HIFU holds potential to enable fully non-invasive treatment of these patients, more technical work is needed to develop a routinely used treatment modality. MR Imaging and energy delivery in the pancreas is challenging because it is located in the upper abdominal area, is subject to respiratory motion and air in the digestive tract leads to artifacts in the images. In this dissertation, new MRI methods were introduced and investigated to improve MRI temperature monitoring and MRI planning of the treatment procedure. In addition, near the pancreas, major vessels and nerves are present, that can be visualized using MRI techniques developed in this thesis. The celiac plexus, for example, a nerve structure that plays a major role in pain generation in these patients, and is therefore a target in pain management. While the work presented in this manuscript introduces promising solutions, future step should be carried towards real time implementation and clinical evaluation of these solutions

Development of MRI methods for guidance of focused ultrasound treatment of pancreatic tumors

MR guided High Intensity Focused Ultrasound (MR-HIFU) is a promising non-invasive therapeutic modality. It makes use of ultrasound waves to cause localized heating of a target volume, e.g. a tumor, deep inside the patient’s body. MRI is used to plan, monitor and evaluate the treatment procedure, by means of high-resolution imaging and MR thermometry techniques that allow real-time temperature mapping. Currently, pancreatic cancer patients have a poor prognosis. While MR-HIFU holds potential to enable fully non-invasive treatment of these patients, more technical work is needed to develop a routinely used treatment modality. MR Imaging and energy delivery in the pancreas is challenging because it is located in the upper abdominal area, is subject to respiratory motion and air in the digestive tract leads to artifacts in the images. In this dissertation, new MRI methods were introduced and investigated to improve MRI temperature monitoring and MRI planning of the treatment procedure. In addition, near the pancreas, major vessels and nerves are present, that can be visualized using MRI techniques developed in this thesis. The celiac plexus, for example, a nerve structure that plays a major role in pain generation in these patients, and is therefore a target in pain management. While the work presented in this manuscript introduces promising solutions, future step should be carried towards real time implementation and clinical evaluation of these solutions

Evaluation of common proton resonance frequency shift based MR Thermometry methods in the pancreas

International audienc

A planning strategy for combined motion-assisted/gated MR guided focused ultrasound treatment of the pancreas

Objective: To develop and evaluate a combined motion-assisted/gated MRHIFU heating strategy designed to accelerate the treatment procedure by reducing the required number of sonications to ablate a target volume in the pancreas. Methods: A planning method for combined motion-assisted/gated MRHIFU using 4D-MRI and motion characterization is introduced. Six healthy volunteers underwent 4D-MRI for target motion characterization on a 3.0-T clinical scanner. Using displacement patterns, simulations were performed for all volunteers for three sonication approaches: gated, combined motion-assisted/gated, and static. The number of sonications needed to ablate the pancreas head was compared. The influence of displacement amplitude and target volume size was investigated. Spherical target volumes (8, 15, 20 and 34 mL) and displacement amplitudes ranging from 5 to 25 mm were evaluated. For this case, the number of sonications required to ablate the whole target was determined. Results: The number of required sonications was lowest for a static target, 62 on average (range 49-78). The gated approach required most sonications, 126 (range 97-159). The combined approach was almost as efficient as the hypothetical static case, with an average of 78 (range 53-123). Simulations showed that with a 5-mm displacement amplitude, the target could be treated by making use of motion-assisted MRHIFU sonications only. In that case, this approach allowed the lowest number of sonication, while for 10 mm and above, the number of required sonications increased. Conclusion: The use of a combined motion-assisted/gated MRHIFU strategy may accelerate tumor ablation in the pancreas when respiratory-induced displacement amplitudes are between 5 and 10 mm

A planning strategy for combined motion-assisted/gated MR guided focused ultrasound treatment of the pancreas

Objective: To develop and evaluate a combined motion-assisted/gated MRHIFU heating strategy designed to accelerate the treatment procedure by reducing the required number of sonications to ablate a target volume in the pancreas. Methods: A planning method for combined motion-assisted/gated MRHIFU using 4D-MRI and motion characterization is introduced. Six healthy volunteers underwent 4D-MRI for target motion characterization on a 3.0-T clinical scanner. Using displacement patterns, simulations were performed for all volunteers for three sonication approaches: gated, combined motion-assisted/gated, and static. The number of sonications needed to ablate the pancreas head was compared. The influence of displacement amplitude and target volume size was investigated. Spherical target volumes (8, 15, 20 and 34 mL) and displacement amplitudes ranging from 5 to 25 mm were evaluated. For this case, the number of sonications required to ablate the whole target was determined. Results: The number of required sonications was lowest for a static target, 62 on average (range 49-78). The gated approach required most sonications, 126 (range 97-159). The combined approach was almost as efficient as the hypothetical static case, with an average of 78 (range 53-123). Simulations showed that with a 5-mm displacement amplitude, the target could be treated by making use of motion-assisted MRHIFU sonications only. In that case, this approach allowed the lowest number of sonication, while for 10 mm and above, the number of required sonications increased. Conclusion: The use of a combined motion-assisted/gated MRHIFU strategy may accelerate tumor ablation in the pancreas when respiratory-induced displacement amplitudes are between 5 and 10 mm

A planning strategy for combined self-scanned/gated MR- HIFU treatment in the pancreas

International audienc

A planning strategy for combined self-scanned/gated MR- HIFU treatment in the pancreas

International audienc

Modélisation des sites instrumentés et évaluation des flux d’azote

Les deux modèles NitroScape et TNT2 ont été appliqués pour simuler la cascade de l'azote sur les quatre sites instrumentés du projet : Naizin en Bretagne, OSOS en Centre-Val de Loire, Avenelles en Île-de-France et Auradé en Occitanie. Ces sites sont contrastés par leurs structures paysagères, leur étendue spatiale, topographie et contexte pédoclimatique, ainsi que par leurs pratiques agricoles et d'élevage. Les deux modèles permettent de simuler de manière spatialisée et dynamique les ordres de grandeur des flux des différentes formes d'azote (volatilisation et dépôt d'ammoniac, pertes directes et indirectes de N 2 O par dénitrification et nitrification, minéralisation, lixiviation de nitrates, prélèvement et restitution par les cultures) dans les différents compartiments des paysages (terrestre, aquatique, aérien). Les dynamiques des flux d'eau et d'azote à l'exutoire, qui intègre en un point l'ensemble des processus spatialisés du site, sont plutôt bien représentées par les modèles. Mais le manque de données ne permet pas toujours d'évaluer de manière précise la répartition spatiale des flux d'azote et l'intensité des processus de transfert et de transformation (e.g. présence d'animaux au pâturage, porosité des sols). Ce manque de données ne permet pas de statuer sur l'intensité des flux qui interagissent et se compensent (e.g. minéralisation, dénitrification, volatilisation), et différentes conditions initiales ont produit des flux simulés d'azote similaires à l'exutoire. L'analyse de sensibilité des modèles a permis de hiérarchiser les processus et les facteurs d'entrée les plus influant sur les variables cibles (e.g. pertes NO 3 , N 2 O, NH 3 , bilans N, rendements) et sur lesquelles il est prioritaire de focaliser les mesures. Les résultats obtenus sur les sites sont présentés, discutés et comparés. Ils montrent la nécessité de développements supplémentaires pour mieux représenter les structures paysagères et les flux d'azote (e.g. zones drainées, sols argileux dont les propriétés physiques évoluent au cours de l'année, paramétrisations de la diversité des cultures). Dénitrification moyenne (kg N/ha/an) calculée par les modèles, spatialisée (cartes) et intégrée (encadrés noirs) sur les quatre sites du projet

Psychiatric symptoms and mortality in older adults with major psychiatric disorders: results from a multicenter study

International audienc