T2ρ and T1ρ adiabatic relaxations and contrasts
T2ρ and T1ρ adiabatic relaxations and contrasts
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DOI：
10.2174/157341108783339115
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发表时间：
2008-01-01
影响因子：
1.8
通讯作者：
Garwood, Michael
中科院分区：
文献类型：
--
作者：
Michaeli, Shalom;Sorce, Dennis J.;Garwood, Michael
旋转坐标系（T-2 ρ）中的横向弛豫是在90度激发脉冲之后没有脉冲间时间间隔的绝热全通（AFP）射频（RF）脉冲序列期间的主要弛豫机制。磁化分量保持横向于随时间变化的有效场，并以时间常数T-2 ρ进行弛豫。旋转坐标系中的纵向弛豫（T-1 ρ）是在激发脉冲之前放置的AFP RF脉冲序列期间的主要弛豫机制。这里，磁化沿着时间相关的有效场在绝热旋转过程中进行弛豫与时间常数T-1 ρ。本文详细描述了绝热脉冲期间由于偶极相互作用和交换引起的旋转坐标系弛豫。交换诱导和偶极相互作用的贡献取决于所使用的绝热脉冲的调制函数。固有的旋转帧弛豫速率常数对旋转帧中的有效频率（ω（eff））处的波动敏感，并且这在两种类型的AFP脉冲期间被不同地调制。这可能导致评估T-1 rho和T-2 rho弛豫受偶极弛豫途径和人脑组织中交换的影响的可能性，并提供在MRI中产生T-1 rho和T-2 rho对比的方法。
Transverse relaxation in the rotating frame (T-2 rho) is the dominant relaxation mechanism during a train of adiabatic full passage (AFP) radiofrequency (RF) pulses with no interpulse time intervals placed after the 90 degrees excitation pulse. The magnetization components remain transverse to the time-dependent effective field and undergo relaxation with the time constant T-2 rho. Longitudinal relaxation in the rotating frame (T-1 rho) is the dominant relaxation mechanism during a train of AFP RF pulses placed prior to an excitation pulse. Here, magnetization is aligned along the time-dependent effective field during adiabatic rotation undergoes relaxation with the time constant T-1 rho. A detailed description of rotating frame relaxations due to dipolar interactions and exchange during adiabatic pulses is presented herein. The exchange-induced and dipolar interaction contributions depend on the modulation functions of the adiabatic pulses used. The intrinsic rotating frame relaxation rate constant is sensitive to fluctuations at the effective frequencey (omega(eff)) in the rotating frame, and this is modulated differently during the two types of AFP pulses. This may lead to the possibility to assess T-1 rho and T-2 rho relaxation influenced by dipolar relaxation pathways and exchange in human brain tissue and provide a means to generate T-1 rho and T-2 rho contrasts in MRI.