Runge V M, Wood M L, Kaufman D M, Traill M R, Nelson K L
Department of Radiology, Tufs University, New England Medical Center Hospitals, Boston, Massachusetts 02111.
Radiographics. 1988 May;8(3):507-31. doi: 10.1148/radiographics.8.3.3380992.
The path to good head and spine images is narrow and treacherous. We have attempted to give the traveller a small but important set of basic rules, enabling him to cross with success. 1. Averaging can be used to achieve sufficient SNR for thin sections, but the cost in terms of scan time is high. Zooming the image (reducing the field of view) should generally be avoided, as the price in terms of SNR is very high. 2. Rectangular pixels and half-Fourier imaging are two methods for decreasing scan time. HFI, which produces high spatial resolution images, can be used when the SNR is not a limiting factor. Rectangular pixels improve the SNR, but decrease resolution. 3. To achieve good T1 contrast with spin echo imaging, set TE less than or equal to 20 msec. and TR less than or equal to 600 msec. For T2 weighted images, a TR between 2.0 and 3.0 sec. is preferred, typically with two echoes: for example, TEs of 25 and 90 msec. 4. Better slice profiles or gaps between slices can be used to combat slice-to-slice interference. This results in improved SNR on T1 weighted images and improved contrast on T2 weighted images. 5. Low bandwidth techniques may be used to improve the SNR on both T1 and T2 weighted images. Chemical shift artifact puts a finite limit on the extent to which this can be applied. 6. Motion compensating gradients are a tremendous boon to MRI and should be utilized in all possible head and spine applications. These reduce image degradation from CSF and vessel pulsation, as well as from involuntary motion. 7. Fast imaging techniques can be used in 2-D multislice mode to decrease scan time. Unfortunately the T2 contrast with this approach is far inferior to that of spin echo technique. 3-D FLASH, with 1 mm. sections, T1 contrast superior to spin echo technique, and the potential for high resolution reformatted images, may replace conventional 2-D, T1 weighted, spin echo imaging. Pulse techniques that combine all the advantages mentioned lie in the future. For example, one possible approach is a T2 weighted head screen that incorporates low bandwidth technique and HFI. This would produce high resolution images with reasonable SNR in approximately half the present scan time. Despite any further new developments, the trade-off between image quality and scan time will likely always remain.(ABSTRACT TRUNCATED AT 400 WORDS)
获得优质头部和脊柱图像的道路狭窄且充满险阻。我们试图为探索者提供一小套但却重要的基本规则，使其能够成功跨越。1. 对于薄层扫描，平均法可用于获得足够的信噪比，但扫描时间成本很高。一般应避免缩放图像（缩小视野），因为信噪比方面的代价非常高。2. 矩形像素和半傅里叶成像法是两种减少扫描时间的方法。当信噪比不是限制因素时，可使用能产生高空间分辨率图像的高分辨率成像（HFI）。矩形像素可提高信噪比，但会降低分辨率。3. 要通过自旋回波成像获得良好的T1对比度，设置TE小于或等于20毫秒，TR小于或等于600毫秒。对于T2加权图像，TR在2.0至3.0秒之间较为理想，通常有两个回波：例如，TE为25和90毫秒。4. 可使用更好的层面轮廓或层面间间隙来对抗层面间干扰。这会提高T1加权图像的信噪比，并改善T2加权图像的对比度。5. 低带宽技术可用于提高T1和T2加权图像的信噪比。化学位移伪影对其应用范围设置了有限的限制。6. 运动补偿梯度对磁共振成像（MRI）来说是极大的福音，应在所有可能的头部和脊柱检查中加以利用。这些可减少脑脊液和血管搏动以及非自主运动造成的图像退化。7. 快速成像技术可用于二维多层模式以减少扫描时间。不幸的是，这种方法的T2对比度远逊于自旋回波技术。具有1毫米层厚、T1对比度优于自旋回波技术且有生成高分辨率重组图像潜力的三维快速扰相梯度回波（3-D FLASH），可能会取代传统的二维T1加权自旋回波成像。结合上述所有优点的脉冲技术尚待未来实现。例如，一种可能的方法是采用结合低带宽技术和高分辨率成像的T2加权头部筛查。这将在大约目前扫描时间的一半内生成具有合理信噪比的高分辨率图像。尽管会有进一步的新进展，但图像质量和扫描时间之间的权衡可能始终存在。（摘要截选至400字）
