Hsieh Ching-Yi, Cheng Yu-Chung N, Neelavalli Jaladhar, Haacke E Mark, Stafford R Jason
Medical Physics Program, Wayne State University, Detroit, MI 48201.
Department of Radiology, Wayne State University, Detroit, MI 48201.
Magn Reson Imaging. 2015 May;33(4):420-36. doi: 10.1016/j.mri.2015.01.004. Epub 2015 Jan 26.
A new method is developed to measure the magnetic susceptibilities and radii of small cylinder-like objects at arbitrary orientations accurately. This method for most biological substances only requires a standard gradient echo sequence with one or two echo times, depending on the orientation of an object relative to the main magnetic field. For objects oriented at the magic angle, however, this method is not applicable. As a byproduct of this method, the cross-sectional area as well as signals inside and outside the object can be determined. The uncertainty of each measurement is estimated from the error propagation method. Partial volume, dephasing, and phase aliasing effects are naturally included in the equations of this method. A number of simulations, phantom, and pilot in-vivo human studies are carried out to validate the theory. When the maximal phase value at the boundary of a given cylindrical object is larger than 3 radians, and the phase inside the object is more than 1 radian, the susceptibility can be accurately quantified within 15%. The radius of the object can be determined to subpixel accuracy. This is the case when the signal-to-noise ratio inside the object is about 6:1 or higher and the radius of the object is about one pixel or larger. These conditions are realistic when considering medullary and pial veins for example.
开发了一种新方法，可精确测量任意取向的小圆柱状物体的磁化率和半径。对于大多数生物物质，此方法仅需要具有一两个回波时间的标准梯度回波序列，具体取决于物体相对于主磁场的取向。然而，对于以魔角取向的物体，此方法不适用。作为该方法的一个副产品，可以确定物体的横截面积以及物体内部和外部的信号。通过误差传播方法估计每次测量的不确定性。该方法的方程中自然包含部分体积、去相位和相位混叠效应。进行了大量模拟、体模和人体初步研究以验证该理论。当给定圆柱形物体边界处的最大相位值大于3弧度，且物体内部的相位大于1弧度时，磁化率可在15%的精度内准确量化。物体的半径可以确定到亚像素精度。例如，当物体内部的信噪比约为6:1或更高且物体的半径约为一个像素或更大时，就是这种情况。在考虑髓静脉和软脑膜静脉时，这些条件是现实的。
