SPECTRAL-SPATIAL PULSES FOR REDUCED DISPLACEMENT ARTIFACTS AT 7 TESLA

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 对于高场（>= 3 T）的局部MR波谱（MRS），激发/重聚焦体积的化学位移配准不良是一个主要问题。 这是因为可实现的峰值RF幅度通常类似于较低场系统（具有相同尺寸的发射线圈），但是要成像的化学位移的范围成比例地更大。 使用高带宽饱和脉冲来修整感兴趣体积的未配准边缘，以RF加热为代价，可以减少这种情况。 我们一直在探索使用频谱空间脉冲的方法，它没有移位伪影。 方法和讨论： 传统的切片选择性激励和重聚焦脉冲以恒定的切片选择梯度沿着传输。 与激励k空间形式主义[1]相反，该梯度导致通过kz与时间的单个成角度的线。 该图案的傅里叶变换倾斜相同的角度。 这种倾斜是化学位移配准不良的根源。 利用与频谱空间脉冲[2，3]一起使用的振荡梯度，其给出了通过kz与时间的锯齿形轨迹，可以在由振荡频率定义的带宽上完全消除这种倾斜。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. For localized MR spectroscopy (MRS) at high field (>= 3 T), chemical shift misregistration of the excited/refocused volume is a major concern. This is because the peak achievable RF amplitude is typically similar to lower field systems (with the same sized transmit coil), but the range of chemical shifts to be imaged is proportionally larger. This is reduced using high bandwidth saturation pulses to trim the misregistered edges of the volume of interest, at the cost of RF heating. We have been exploring the approach of using spectral-spatial pulses, which have no shift artifact. Methods and Discussion: Conventional slice-selective excitation and refocusing pulses are transmitted along with a constant slice-select gradient. Invoking the excitation k-space formalism [1], this gradient results in a single, angled line through kz vs. time. The Fourier transform of this pattern is tilted by the same angle. This tilt is the source of chemical-shift mis-registration. With the oscillating gradient used with spectral-spatial pulses [2,3], which gives a zig-zag trajectory through kz vs. time, this tilt can be entirely removed over the bandwidth defined by the oscillation frequency.