Vinogradov Elena, Zhang Shanrong, Lubag Angelo, Balschi James A, Sherry A Dean, Lenkinski Robert E
Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
J Magn Reson. 2005 Sep;176(1):54-63. doi: 10.1016/j.jmr.2005.05.016.
Application of the exchange-sensitive, low-power RF pulses positioned on the bulk water resonance for imaging of the effects of PARACEST agents is proposed as an alternative to the standard CW off-resonance irradiation. Specifically, we applied a low-power WALTZ-16 RF train, with the 90 degrees pulse unit replaced by a pulse of the fixed length (WALTZ-16*). Using this sequence, the bulk water signal was found to be sensitive to exchange lifetimes with PARACEST complex bound protons, the transverse relaxation time of bulk water, and longitudinal relaxation time of bound protons. In this report, the concept of using WALTZ-16* to "activate" a PARACEST effect is introduced and some of the salient features of this technique with respect to experimental conditions and performance levels are discussed. Computational predictions are verified and explored by comparison with experimental spectroscopic and imaging data. It is shown that WALTZ-16* can be used to detect PARACEST agents with an RF intensity as low as 200 Hz for concentrations as low as a few tens of microM for lanthanide chelates having appropriate water-exchange rates (Tm,Dy).
有人提出，将位于体水共振处的交换敏感型低功率射频脉冲应用于顺磁化学交换饱和转移（PARACEST）剂效应成像，作为标准连续波非共振照射的替代方法。具体而言，我们应用了一种低功率的WALTZ-16射频脉冲序列，其中90度脉冲单元被固定长度的脉冲（WALTZ-16*）取代。使用该序列时，发现体水信号对与PARACEST复合物结合质子的交换寿命、体水的横向弛豫时间以及结合质子的纵向弛豫时间敏感。在本报告中，引入了使用WALTZ-16来“激活”PARACEST效应的概念，并讨论了该技术在实验条件和性能水平方面的一些显著特征。通过与实验光谱和成像数据进行比较，验证并探索了计算预测结果。结果表明，对于具有适当水交换速率（Tm，Dy）的镧系螯合物，WALTZ-16可用于检测浓度低至几十微摩尔、射频强度低至200赫兹的PARACEST剂。
