Department of Physical Sciences, Sunnybrook Research Institute, Toronto, Canada.
Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada.
Magn Reson Med. 2019 Nov;82(5):1684-1699. doi: 10.1002/mrm.27856. Epub 2019 Jun 22.
To compare magnetization transfer (MT) and CEST effects between 1.5T and 3T in phantom and in vivo experiments.
A pulsed saturation scheme using block-shaped pulses separated by gaps was used to overcome the single RF amplifier duty cycle limitations of a clinical 1.5T scanner. Modeling was performed by incorporating the extended phase graph formalism into a Bloch-McConnell simulation. Two saturation pulse types (with long and short pulses) were used. Estimated parameters for MT (the semi-solid pool fraction, M ; the semi-solid transverse relaxation time, T ) and CEST (asymmetry; areas) were compared between 1.5T and 3T in phantoms and in the healthy brain.
Improved fits were shown after inclusion of extended phase graphs. Semi-solid pool fractions in phantom (for agar with ammonium chloride) were higher for short compared to long pulses at 3T (by 19% over all concentrations) and higher at 1.5T compared to 3T (by 5%) using short pulses. In the in vivo experiments, differentiation of white and gray matter was seen in the brain at both field strengths with improved white-gray matter contrast at 3T. In white matter, the mean semi-solid fractions were 18 ± 2% at 3T and 15 ± 2% at 1.5T. The CEST asymmetry in white matter was negative (-4.9 ± 0.4%) at 3T and zero (0.0 ± 0.3%) at 1.5T.
The pulsed saturation method with short pulses, using the extended phase graph formalism in the Bloch McConnell simulations, led to improved model fits to the data, when compared to those without extended phase graphs.
在体模和活体实验中比较 1.5T 和 3T 之间的磁化转移（MT）和 CEST 效应。
使用由间隙隔开的块状脉冲的脉冲饱和方案克服了临床 1.5T 扫描仪中单个射频放大器工作周期的限制。通过将扩展相位图形式纳入 Bloch-McConnell 模拟中进行建模。使用两种饱和脉冲类型（长脉冲和短脉冲）。在体模和健康大脑中比较了 1.5T 和 3T 之间的 MT（半固体池分数，M；半固体横向弛豫时间，T）和 CEST（不对称；面积）的估计参数。
在包含扩展相位图后，显示出了更好的拟合。在 3T 时，与长脉冲相比，短脉冲下体模（含氯化铵琼脂）中的半固体池分数更高（所有浓度下均高 19%），而在 1.5T 时，与 3T 相比，短脉冲下的半固体池分数更高（高 5%）。在体内实验中，在两种场强下都可以在大脑中看到白质和灰质的分化，在 3T 时，白质-灰质对比度得到改善。在白质中，3T 时的平均半固体分数为 18 ± 2%，1.5T 时为 15 ± 2%。在白质中，CEST 不对称性为-4.9 ± 0.4%（3T）和 0.0 ± 0.3%（1.5T）。
在 Bloch McConnell 模拟中使用短脉冲的脉冲饱和方法，以及扩展相位图形式，与不使用扩展相位图的方法相比，导致数据的模型拟合得到改善。
