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

考虑到乳腺癌的高患病率和早期预后的极大改善，早期发现乳腺癌是至关重要的。然而，X光乳房X光检查会导致大量的假阳性结果。已有研究表明，扩散加权磁共振成像(DWI)可以用来避免很大一部分不必要的活检。尽管DWI在女性乳房成像中取得了成功，但进一步提高敏感度将是非常有价值的。对于DWI，产生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，增强的信号质量可以转化为更高的图像分辨率，以更好地评估微小病变。其次，体内DWI测量通常只与组织结构间接相关，因为在梯度脉冲应用过程中，由于水分子的大量运动，它们只产生所谓的表观参数。产生短脉冲的超高梯度幅度可以获得与组织结构更直接相关的新参数空间，并显著增强肿瘤的特征。因此，本提案的目的是开发一种新的设备-“高功率扩散探头”-在女性乳房局部提供比目前临床MR成像仪可用的高一个数量级的梯度幅度(预期平均梯度幅度和1500mT/m)。这一建议建立在第一阶段的基础上，在此阶段，构建了一个低占空比的乳房梯度线圈，证明了达到这些前所未有的梯度幅度的可行性。所有与安全性相关的方面都进行了评估，包括潜在的神经刺激以及确保体内应用的可能性的热和机电特性。计划在第二阶段构建一个能够满足快速多层成像所需的高占空比操作的高功率乳房梯度线圈。这将使用新的制造技术来实现，特别是铜3D打印，这将导致与第一个原型相比，热负荷更低。具有更高导热系数的材料和多层线圈设计也将被开发。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磁共振扫描仪中，并用于志愿者神经刺激研究。为了实现并行成像能力，将构建一个多通道射频接收器线圈。将实现常规DWI的伪影补偿技术以及高级DWI序列，例如Q空间成像和与时间相关的DWI。使用超高梯度区分乳腺良恶性病变的可能性将在一项验证性患者研究中进行评估。还将探索在身体其他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.