Periodic Reporting for period 2 - SpreadMRI (Ultra-Fast, Spread-Spectrum Magnetic Resonance Imaging) Reporting period: 2021-03-01 to 2022-08-31 Summary of the context and overall objectives of the project A major limitation of MR is its rather low imaging speed compared, for example, to ultra sound, optical imaging or computerized tomography. However, imaging speed is one of the key factors if rapid changes need to be captured at a high spatial and temporal resolution. Examples are cardiac imaging to resolve the 3D beating heart at a high temporal and spatial scale during single breath hold, or time resolved imaging of the flow patterns of the entire arterial system in the brain to assess potential risks of stenosis, to name just a few. SpreadMRI investigates two novel and general concepts that aim to boost imaging speed by another factor of 2 to 10 compared to existing methods. The proposed techniques and concepts will open a huge variety of novel application of MR, both in the field of basic research and clinical routine applications. These concepts, have the potential to impact the field of MR that is comparable to the introduction of parallel imaging some two decades ago. SpreadMRI applies a spectral spin modulation that so far has not been employed in MR imaging, located between the kHz range of switched gradients and the hundreds of MHz range of the Larmor frequency. SpreadMRI is based on the rapid dynamic (up to MHz) and local modulation of magnetic fields produced by current loops (B0) and/or radio frequency loops (B1). These fields are modulated dynamically during signal acquisition to imprint local and distinct signal characteristics into the spin arrangement, which can be interpreted as a unique fingerprint onto confined regions within the object. Ultra-rapid imaging with SpreadMRI will allow investigating physiological and functional processes of living tissue with hitherto unrivalled temporal and spatial resolution, and will substantially change the landscape of fast MR imaging (and spectroscopy). The possibility to capture high spatially resolved dynamic information and the specific approach to encode MR signals with SpreadMRI will lead to major changes in the hardware and software environment of current MR-scanners. It includes a rich variety of challenges and developments, which will not only provide new insight within the areas covered by the proposal, but will definitely benefit conventional diagnostic MRI. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far A new local magnetic coil array (8 square loops) was built with geometry compatible with a shielded transmit/receive RF coil for in-vivo head imaging at 9.4T. With the temperature constantly monitored, each coil has its current independently driven and monitored by the power amplifiers, which were controlled by a high-speed signal generator/monitor device synchronized with the scanner. Several approaches have been applied to evaluate the safety of local magnetic coils for in-vivo measurement, such as computation of the electrical field distribution in a brain model, evaluation of potential neuro-stimulations with a neuron model of human brain to check and noise level checks of local coils during operation. First novel results of dynamic sensitivity profile switching have been published where receive sensitivity modulation was achieved by introducing PIN diodes in the receive loops, which allow rapid switching of capacitances in both arms of each loop coil and by that alter receive profiles, resulting in two distinct receive sensitivity configurations. A prototype 8-channel reconfigurable receive coil for human head imaging was built and MR measurements were performed in both phantom and human subject. A modified SENSE reconstruction for time-varying sensitivities was formulated and g-factor calculations were performed to investigate how modulation of receive sensitivity profiles during image encoding can improve parallel imaging reconstruction. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) We could experimentally demonstrate, that both novel approaches to speed up MRI are fully functionable. We believe that these very encouraging results will lead to further novel concepts in MRI acquisition that so far have not been used. Accelerated signal acquisition using locally modulated magnetic fields
