Melhem E R, Jara H, Yucel E K
Department of Radiology, Boston University Medical Center, MA 02118, USA.
J Magn Reson Imaging. 1996 Nov-Dec;6(6):903-8. doi: 10.1002/jmri.1880060611.
Using a T1-weighted hybrid rapid acquisition with relaxation enhancement (RARE) MR sequence that implements an echo-to-view mapping scheme termed "low-high profile order," we evaluated signal intensity changes in different brain tissues as a function of number of slices, interslice gap, and echo train length (ETL). We also measured phase-encode and frequency-encode noise as well as blurring artifacts along the phase-encode direction as a function of ETL. Off-resonance magnetization transfer effects were demonstrated to be responsible for signal intensities changes in white matter and gray matter when using multislice techniques. These effects are amplified by increasing the number of slices and ETL. Due to the nature of the implemented echo-to-view mapping scheme, no on-resonance magnetization transfer effects were observed from the intraslice echo train. Selective background (white matter and gray matter) suppression in multislice T1-weighted hybrid RARE, secondary to off-resonance magnetization transfer effects, may provide better contrast resolution of enhancing central nervous system (CNS) lesions at much shorter scan time as compared to conventional spin-echo T1-weighted sequences. This improvement in contrast resolution as a function of ETL may be limited by worsening phase-encode noise and blurring artifacts.
我们使用一种T1加权混合快速采集与弛豫增强（RARE）磁共振序列，该序列采用一种称为“低-高轮廓顺序”的回波到视图映射方案，评估了不同脑组织中信号强度随切片数量、层间距和回波链长度（ETL）的变化。我们还测量了相位编码和频率编码噪声以及沿相位编码方向的模糊伪影随ETL的变化。当使用多层技术时，失谐磁化传递效应被证明是导致白质和灰质信号强度变化的原因。这些效应会随着切片数量和ETL的增加而放大。由于所采用的回波到视图映射方案的性质，在切片内回波链中未观察到共振磁化传递效应。多层T1加权混合RARE中由于失谐磁化传递效应导致的选择性背景（白质和灰质）抑制，与传统自旋回波T1加权序列相比，在更短的扫描时间内可能提供更好的增强中枢神经系统（CNS）病变的对比分辨率。这种作为ETL函数的对比分辨率的提高可能会受到相位编码噪声恶化和模糊伪影的限制。
