Centre for Functional and Metabolic Mapping, Robarts Research Institute, The University of Western Ontario, PO Box 5015, 100 Perth Drive, London, Ontario, N6A 5K8, Canada.
Phys Med Biol. 2010 Jan 21;55(2):497-514. doi: 10.1088/0031-9155/55/2/011. Epub 2009 Dec 21.
The never ending quest for higher magnetic field strengths in MRI and MRS has led to small and medium bore scanners at 9.4 T and above for both human and animal use; however, these bore diameters restrict the size of object that can be accommodated when using a conventional gradient coil. By replacing a cylindrical gradient-coil insert with a single-sided gradient coil, the scanner's functionality can be extended to include localized imaging of wider samples. As a prototype, a three-axis, cradle-shaped gradient coil was designed, fabricated and implemented in a 9.4 T animal MRI scanner. Since gradient fields are required only to be monotonic over the desired field of view, the cradle gradient coil was designed to produce high gradient efficiencies (up to 2.25 mT m(-1) A(-1) over a 5 cm imaging region) at the expense of gradient linearity. A dedicated three-dimensional algorithm was developed to correct the resultant image distortion. Preliminary images of a grid phantom and a mouse demonstrated the fidelity of the algorithm in correcting image distortion of greater than 200%. Eddy currents were measured along each gradient axis. A large 65.2 (Hz mT(-1) m) B(0) eddy current was produced by the y-axis, suggesting potential limitations of single-sided gradient coils.
在 MRI 和 MRS 中不断追求更高的磁场强度，导致了用于人体和动物的 9.4T 及以上的小中型孔径扫描仪；然而，这些孔径直径限制了在使用常规梯度线圈时可以容纳的物体大小。通过用单边梯度线圈替换圆柱形梯度线圈插入件，可以扩展扫描仪的功能，包括对更宽样本的局部成像。作为原型，设计、制造并在 9.4T 动物 MRI 扫描仪中实现了三轴、摇篮形梯度线圈。由于梯度场仅需要在期望的视野内单调变化，因此摇篮梯度线圈被设计为在牺牲梯度线性度的情况下产生高梯度效率（在 5cm 成像区域内高达 2.25mT m^(-1) A^(-1)）。开发了一种专用的三维算法来校正所得的图像失真。网格幻影和老鼠的初步图像表明，该算法在校正超过 200%的图像失真方面具有很高的准确性。沿着每个梯度轴测量了涡流。y 轴产生了一个大的 65.2(Hz mT^(-1) m)B(0)涡流，这表明单边梯度线圈可能存在局限性。
