Xu Junzhong, Does Mark D, Gore John C
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, USA.
Magn Reson Med. 2009 Apr;61(4):828-33. doi: 10.1002/mrm.21793.
Magnetic resonance imaging measurements of the apparent rate of water diffusion in tumors are sensitive to variations in tissue cellularity, which have been shown useful for characterizing tumors and their responses to treatments. However, because of technical limitations on most MRI systems, conventional pulse gradient spin echo (PGSE) methods measure relatively long time scales, during which water molecules may encounter diffusion barriers at multiple spatial scales, including those much greater than typical cell dimensions. As such they cannot distinguish changes on subcellular scales from gross changes in cell density. Oscillating gradient spin echo (OGSE) methods have the potential to distinguish effects on restriction at much shorter time and length scales. Both PGSE and OGSE methods have been studied numerically by simulating diffusion in a three-dimensional, multicompartment tissue model. The results show that conventional measurements with the PGSE method cannot selectively probe variations over short length scales and, therefore, are relatively insensitive to intracellular structure, whereas results using OGSE methods at moderate gradient frequencies are affected by variations in cell nuclear sizes and can distinguish tissues that differ only over subcellular length scales. This additional sensitivity suggests that OGSE imaging may have significant advantages over conventional PGSE methods for characterizing tumors.
磁共振成像测量肿瘤中水分扩散的表观速率对组织细胞密度的变化敏感，这已被证明有助于表征肿瘤及其对治疗的反应。然而，由于大多数MRI系统存在技术限制，传统的脉冲梯度自旋回波（PGSE）方法测量的时间尺度相对较长，在此期间水分子可能会在多个空间尺度上遇到扩散障碍，包括那些远大于典型细胞尺寸的障碍。因此，它们无法区分亚细胞尺度的变化和细胞密度的总体变化。振荡梯度自旋回波（OGSE）方法有潜力在更短的时间和长度尺度上区分限制效应。PGSE和OGSE方法都已通过在三维多隔室组织模型中模拟扩散进行了数值研究。结果表明，使用PGSE方法的传统测量无法选择性地探测短长度尺度上的变化，因此对细胞内结构相对不敏感，而在中等梯度频率下使用OGSE方法的结果受细胞核大小变化的影响，并且可以区分仅在亚细胞长度尺度上不同的组织。这种额外的敏感性表明，OGSE成像在表征肿瘤方面可能比传统的PGSE方法具有显著优势。
