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

考虑到乳腺癌的高患病率和早期阶段预后的极大改善，早期发现乳腺癌至关重要。然而，X射线乳腺摄影筛查导致大量的假阳性结果。它已被证明，弥散加权磁共振成像（DWI）可以用来避免大部分不必要的活检。尽管DWI在女性乳腺成像方面取得了成功，但进一步提高灵敏度将具有重要价值。对于DWI，生成扩散加权的梯度系统的性能至关重要。首先，更高的梯度幅度导致更短的回波时间，并且增强的信号质量可以转化为提高的图像分辨率，以便更好地评估小病变。其次，体内DWI测量通常仅与组织结构间接相关，因为它们仅产生所谓的表观参数，这是由于在梯度脉冲应用期间水分子的相当大的运动。导致短脉冲的超高梯度幅度可以允许访问与组织结构更直接相关的新参数空间，并显著增强肿瘤表征。本提案的目的是开发一种新的设备--“高功率扩散探头”--它在女性乳房局部提供比目前临床MR成像仪高一个数量级以上的梯度幅度（预期平均梯度振幅> 1500 mT/m）。该提案建立在第1阶段的基础上，在此期间构建了低占空比乳腺梯度线圈，证明了达到这些前所未有的梯度幅度的可行性。已评估了所有安全性相关方面，包括潜在的神经刺激以及确保体内应用可能性的热和机电性能。计划在第2阶段构建一个高功率乳腺梯度线圈，能够根据快速多层成像的要求进行高占空比操作。这将使用新的制造技术来实现，特别是铜3D打印，与第一个原型相比，这将导致更低的热负荷。第一阶段的原型和第二阶段的高占空比线圈将被集成到临床MR扫描仪中，并用于志愿者神经刺激研究。为了实现并行成像能力，将构建多通道RF接收器线圈。将实施常规DWI的磁共振补偿技术以及高级DWI序列，如q空间成像和时间相关DWI。将在概念验证患者研究中评估使用超高梯度区分良性和恶性乳腺病变的潜力。还将探讨在其他身体部位使用局部梯度线圈的技术和生理可行性。

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.