Deppe Martin H, Parra-Robles Juan, Ajraoui Salma, Parnell Steven R, Clemence Matthew, Schulte Rolf F, Wild Jim M
Academic Radiology, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK.
J Magn Reson Imaging. 2009 Aug;30(2):418-23. doi: 10.1002/jmri.21852.
To compare susceptibility effects in hyperpolarized (3)He lung MRI at the clinically relevant field strengths of 1.5T and 3T.
Susceptibility-related B(0) inhomogeneity was evaluated on a macroscopic scale by B(0) field mapping via phase difference. Subpixel susceptibility effects were quantified by mapping T2. Comparison was made between ventilation images obtained from the same volunteers at both field strengths.
The B(0) maps at 3T show enhanced off-resonance effects close to the diaphragm and the ribs due to susceptibility differences. The average T2 from a voxel (20 x 4 x 4) mm(3) was determined as T2 = 27.8 msec +/- 1.2 msec at 1.5T compared to T2 = 14.4 msec +/- 2.6 msec at 3T. In ventilation images the most prominent effect is increased signal attenuation close to the intrapulmonary blood vessels at higher B(0).
Image homogeneity and T2 are lower at 3T due to increased B(0) inhomogeneity as a consequence of susceptibility differences. These findings indicate that (3)He imaging at 3T has no obvious benefit over imaging at 1.5T, as signal-to-noise ratio (SNR) was comparable for both fields in this work.
在1.5T和3T这两个临床相关场强下，比较超极化³He肺部磁共振成像（MRI）中的磁化率效应。
通过相位差进行B₀场映射，在宏观尺度上评估与磁化率相关的B₀不均匀性。通过映射T₂来量化亚像素磁化率效应。对相同志愿者在两个场强下获得的通气图像进行比较。
3T时的B₀图显示，由于磁化率差异，在靠近膈肌和肋骨处的失谐效应增强。在1.5T时，体素（20×4×4）mm³的平均T₂确定为T₂ = 27.8毫秒±1.2毫秒，而在3T时为T₂ = 14.4毫秒±2.6毫秒。在通气图像中，最显著的效应是在较高B₀时肺内血管附近信号衰减增加。
由于磁化率差异导致B₀不均匀性增加，3T时的图像均匀性和T₂较低。这些发现表明，在这项工作中，由于两个场强的信噪比（SNR）相当，3T时的³He成像相对于1.5T成像没有明显优势。
