High-Power Diffusion Probe for Human Breast MRI – Phase 2

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Early detection of breast cancer is of utmost importance considering the high prevalence of this disease and the vastly improved prognosis in early stages. However, x-ray mammography screening results in a high number of false-positive findings. It has been shown that diffusion-weighted magnetic resonance imaging (DWI) can be used to avoid a large fraction of the resulting unnecessary biopsies. Despite the success of DWI for female breast imaging, further improvements in sensitivity would be of great value. For DWI, the performance of the gradient system generating the diffusion weighting is critical. Firstly, higher gradient amplitudes result in shorter echo times, and the enhanced signal quality can be translated to improved image resolution for better assessment of small lesions. Secondly, DWI measurements in vivo are usually only indirectly related to tissue structure since they only yield so-called apparent parameters due to the considerable motion of water molecules during gradient pulse application. Ultra-high gradient amplitudes resulting in short pulses could allow access to a new parameter space more directly related to tissue structure and substantially enhance tumor characterization.Thus, the aim of the present proposal is to develop a new device – a "High-Power Diffusion Probe" – that locally provides more than an order of magnitude higher gradient amplitudes in the female breast than presently available with clinical MR imagers (anticipated mean gradient amplitude > 1500 mT/m). This proposal builds on Phase 1, during which a low-duty-cycle breast gradient coil was constructed demonstrating the feasibility of reaching these unprecedented gradient amplitudes. All safety relevant aspects have been assessed, including potential nerve stimulation as well as thermal and electro-mechanical properties ensuring the possibility for in vivo application. It is planned to construct a high-power breast gradient coil in Phase 2 capable of high-duty-cycle operation as required for fast multi-slice imaging. This will be accomplished using novel manufacturing technologies, in particular copper 3D printing, which will result in lower thermal load compared to the first prototype. Materials with higher thermal conductivity and a multi-layer coil design will also be explored.The prototype from Phase 1 and the high-duty-cycle coil from Phase 2 will be integrated into a clinical MR scanner and used for a volunteer nerve stimulation study. To enable parallel imaging capabilities, a multi-channel RF receiver coil will be constructed. Artifact compensation techniques for conventional DWI will be implemented as well as advanced DWI sequences such as q-space imaging and time-dependent DWI. The potential of differentiating benign and malignant breast lesion using ultra-high gradients will be assessed in a proof-of-concept patient study. The technical and physiological feasibility for using local gradient coils in other body parts will also be explored.