Bottomley P A
General Electric Corporate Research and Development Center Schenectady, New York 12301.
Ann N Y Acad Sci. 1987;508:333-48. doi: 10.1111/j.1749-6632.1987.tb32915.x.
Spatial localization techniques are necessary for in vivo NMR spectroscopy involving heterogeneous organisms. Localization by surface coil NMR detection alone is generally inadequate for deep-lying organs due to contaminating signals from intervening surface tissues. However, localization to preselected planar volumes can be accomplished using a single selective excitation pulse in the presence of a pulsed magnetic field gradient, yielding depth-resolved surface coil spectra (DRESS). Within selected planes, DRESS are spatially restricted by the surface coil sensitivity profiles to disk-shaped volumes whose radii increase with depth, notwithstanding variations in the NMR signal density distribution. Nevertheless, DRESS is a simple and versatile localization procedure that is readily adaptable to spectral relaxation time measurements by adding inversion or spin-echo refocusing pulses or to in vivo solvent-suppressed spectroscopy of proton (1H) metabolites using a combination of chemical-selective RF pulses. Also, the spatial information gathering efficiency of the technique can be improved to provide simultaneous acquisition of spectra from multiple volumes by interleaving excitation of adjacent planes within the normal relaxation recovery period. The spatial selectivity can be improved by adding additional selective excitation spin-echo refocusing pulses to achieve full, three-dimensional point resolved spectroscopy (PRESS) in a single excitation sequence. Alternatively, for samples with short spin-spin relaxation times, DRESS can be combined with other localization schemes, such as image-selected in vivo spectroscopy (ISIS), to provide complete gradient controlled three-dimensional localization with a reduced number of sequence cycles.
对于涉及异质生物体的体内核磁共振波谱分析而言，空间定位技术是必不可少的。仅通过表面线圈核磁共振检测进行定位，对于深层器官通常是不够的，因为来自中间表面组织的污染信号会产生干扰。然而，在脉冲磁场梯度存在的情况下，使用单个选择性激发脉冲可以实现对预选平面体积的定位，从而产生深度分辨表面线圈波谱（DRESS）。在选定平面内，尽管核磁共振信号密度分布存在变化，但DRESS在空间上受到表面线圈灵敏度分布的限制，形成半径随深度增加的盘状体积。尽管如此，DRESS是一种简单且通用的定位方法，通过添加反转或自旋回波重聚焦脉冲，它很容易适用于光谱弛豫时间测量，或者通过化学选择性射频脉冲的组合，适用于质子（1H）代谢物的体内溶剂抑制波谱分析。此外，该技术的空间信息收集效率可以通过在正常弛豫恢复期间交错激发相邻平面来提高，以同时采集多个体积的波谱。通过添加额外的选择性激发自旋回波重聚焦脉冲，可以提高空间选择性，从而在单个激发序列中实现完整的三维点分辨波谱（PRESS）。或者，对于自旋 - 自旋弛豫时间较短的样品，DRESS可以与其他定位方案（如体内图像选择波谱分析（ISIS））相结合，以减少序列循环次数的方式提供完整的梯度控制三维定位。
