FastRelaxMRI

Magnetic Resonance Imaging (MRI) enables to obtain images with high contrasts. Nevertheless, there is a need to develop quantitative methods to obtain a non-subjective scale in order to assess the evolution of a disease, to precisely evaluate the efficacy of a treatment, to monitor minimally-invasive procedures. The actual methods of relaxometry are either time-costly, not accurate, sensitive to respiration-motion or not applicable on short-T2* areas (lungs, bones, surrounding metallic implants). Consequently, this project focus on the development of the measurement of relaxation times in all these difficult conditions. This technical objective gets even more challenging as we intend to apply them for MR-guided therapies, whose specificity is real-time monitoring (both image acquisition and reconstruction). Therefore, the goal of our project is to develop multi-parametric sequences to obtain accurate relaxometry measurements on every organ of the body, and ultra-rapidly for numerous applications. This project is crucial before a world-wide clinical use in order to reduce exam cost, patient discomfort, waiting lists and to increase the accuracy of diagnoses, prognoses and follow-ups of patients. In addition, the project is of huge interest for interventional MR-guidance, especially cryoablation therapies, in need of quantitative real-time data to ensure their safety, their efficiency and their proper use. The project will involve the implementation of 2D non-Cartesian encodings of the k-space and Ultra-short Echo Time (UTE) into MR Gradient Echo sequences on a human research MR system at 3T. An innovative MR sequence enabling to simultaneously measure T1, T2 and T2* relaxation times will be developed. Acceleration techniques including Simultaneous Multi-Slice and Compressed Sensing, in parallel with motion-correction methods (using a Self-Gating module and post-processing in the image domain) will be implemented. Also ultra-fast reconstruction algorithms will be developed through the Gadgetron open-source software. These methodological developments will take place during the first two years, before any application on human volunteers. Then, high-resolution parametric maps of each body area (brain, thorax, abdomen, knees) are expected to be obtained in less than 3 min, which is faster than the current time required to obtain weighted-images for similar spatial resolutions. The new methods will then be applied on a large-animal (rabbit) model of lung tumors. The intended spatial resolution will be 0.5mm in-plane in order to obtain multi-parametric maps of early-growing tumors. The last years of the project will focus on the quantitative characterization of the temperature drop during a percutaneous cryoablation of the rabbit lung tumor in vivo. To do so, temperature values of the tumor and the surrounding lung region should be obtained from the parametric maps every ˜10s. In summary, the originality of the FastRelaxMRI project relies in the combination of multiple techniques within a single multi-parametric sequence so that it can be applied for multi-organ, multi-application human research and clinical routine. Developments within each technique (encodings, motion correction, acceleration) and developments to coordinate them are the novelties of the project. The improvements obtained in this project will be tremendous assets for the diagnosis, prognosis and surveillance of multiple pathologies, and could become the reference method to quantitatively-guide cryoablations.