Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
J Magn Reson Imaging. 2010 Jun;31(6):1530-7. doi: 10.1002/jmri.22196.
To demonstrate the feasibility of two-dimensional selective radio frequency (2DRF) excitations for fast-spin-echo imaging of inner fields-of-view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring.
Fast-spin-echo images (in-plane resolution 1.0 x 1.0 mm(2) or 0.5 x 1.0 mm(2)) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole-body MR system using blipped-planar 2DRF excitations.
Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast-spin-echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single-shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single-shot acquisitions is considerably reduced yielding effectively higher in-plane resolutions.
Inner-FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast-spin-echo (FSE) imaging, in particular at higher static magnetic fields.
演示二维选择性射频（2DRF）激发在快速自旋回波成像内部视场（FOV）中的可行性，以缩短采集时间、减少射频能量沉积并降低图像模糊度。
在 3T 全身磁共振系统上，使用带扰相的平面 2DRF 激发，对体模和健康志愿者进行内部 FOV（40mm，16mm 过采样）的快速自旋回波成像（平面分辨率为 1.0x1.0mm² 或 0.5x1.0mm²）。
将不需要的侧面激发定位在图像层面和层面堆叠之间的盲区，可以产生最小的 2DRF 脉冲持续时间（约 6msec），与快速自旋回波采集的典型回波间隔兼容。对于内部 FOV，回波和重聚焦 RF 脉冲的数量大大减少，与全 FOV（182mm）相比，这减少了约三分之一的射频能量沉积，并缩短了采集时间，例如，涡轮因子为 15 时从 39 秒缩短至 12 秒，或者单次采集时从 900msec 缩短至 280msec。此外，对于单次采集等高涡轮因子，会显著降低图像模糊度，从而有效地提高了平面分辨率。
使用 2DRF 激发进行内部 FOV 采集有助于缩短采集时间、改善图像模糊度，并降低快速自旋回波（FSE）成像的特定吸收率（SAR）限制，特别是在更高的静磁场强度下。
