Bailey Colleen, Moosvi Firas, Stanisz Greg J
Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada; Department of Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Canada.
Magn Reson Med. 2014 May;71(5):1874-87. doi: 10.1002/mrm.24847. Epub 2013 Jun 25.
To map the intra-to-extracellular water exchange rate constant in rat xenografts using a two-compartment model of relaxation with water exchange and a range of contrast agent concentrations and compare with histology.
MDA-MB-231 cells were xenografted into six nude rats. Three bolus injections of gadodiamide were administered. When uptake in the tumor demonstrated a steady-state, T1 data were acquired by spoiled gradient recalled acquisitions at four flip angles. A global fit of data to a two-compartment model incorporating exchange was performed, assuming a distribution volume of 20% of the rat.
Voxels that did not reach steady-state and were excluded from parametric maps tended to be in large necrotic areas. TUNEL-negative (nonapoptotic) regions tended to have well-defined error bounds, with an average intra-to-extracellular exchange rate constant of 0.6 s(-1) . Apoptotic regions had higher exchange, but poorly determined upper bounds, with goodness of fit similar to that for a model assuming infinitely fast exchange. A lower bound of >3 s(-1) was used to establish voxels where the exchange rate constant was fast despite a large upper bound.
Water exchange rates were higher in apoptotic regions, but examination of statistical errors was an important step in the mapping process.
使用具有水交换功能的双室弛豫模型以及一系列造影剂浓度，绘制大鼠异种移植瘤内细胞内到细胞外的水交换速率常数，并与组织学结果进行比较。
将MDA-MB-231细胞异种移植到六只裸鼠体内。给予三次钆双胺团注注射。当肿瘤摄取显示达到稳态时，通过在四个翻转角下进行扰相梯度回波采集来获取T1数据。假设大鼠分布容积为20%，对数据进行全局拟合，使其符合包含交换的双室模型。
未达到稳态并被排除在参数图之外的体素往往位于大的坏死区域。TUNEL阴性（非凋亡）区域往往具有明确的误差范围，细胞内到细胞外的平均交换速率常数为0.6 s(-1)。凋亡区域具有更高的交换率，但上限测定不佳，拟合优度与假设无限快速交换的模型相似。尽管上限较大，但仍使用大于3 s(-1)的下限来确定交换速率常数较快的体素。
凋亡区域的水交换率较高，但检查统计误差是映射过程中的重要一步。
