Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey.
Magn Reson Med. 2011 Sep;66(3):846-58. doi: 10.1002/mrm.22830. Epub 2011 Mar 9.
The ultimate intrinsic signal-to-noise ratio is the highest possible signal-to-noise ratio, and the ultimate intrinsic specific absorption rate provides the lowest limit of the specific absorption rate for a given flip angle distribution. Analytic expressions for ultimate intrinsic signal-to-noise ratio and ultimate intrinsic specific absorption rate are obtained for arbitrary sample geometries. These expressions are valid when the distance between the point of interest and the sample surface is smaller than the wavelength, and the sample is homogeneous. The dependence on the sample permittivity, conductivity, temperature, size, and the static magnetic field strength is given in analytic form, which enables the easy evaluation of the change in signal-to-noise ratio and specific absorption rate when the sample is scaled in size or when any of its geometrical or electrical parameters is altered. Furthermore, it is shown that signal-to-noise ratio and specific absorption rate are independent of the permeability of the sample. As a practical case and a solution example, a uniform, circular cylindrically shaped sample is studied.
最终固有信噪比是可能达到的最高信噪比，而最终固有比吸收率则为给定翻转角分布的比吸收率提供了最低极限。针对任意样本几何形状，我们得到了最终固有信噪比和最终固有比吸收率的解析表达式。这些表达式在感兴趣点与样本表面之间的距离小于波长且样本均匀的情况下有效。以解析形式给出了对样本介电常数、电导率、温度、尺寸和静磁场强度的依赖性，这使得易于评估当样本尺寸缩放或其任何几何或电参数发生变化时，信噪比和比吸收率的变化。此外，还表明信噪比和比吸收率与样本的磁导率无关。作为一个实际案例和解决方案示例，研究了均匀的、圆柱形的样本。
