使用改进的三维快速大角度自旋回波(FLASE)对小梁骨进行自旋回波显微磁共振成像。

Spin-echo micro-MRI of trabecular bone using improved 3D fast large-angle spin-echo (FLASE).

作者信息

Magland J F, Wald M J, Wehrli F W

机构信息

Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104, USA.

出版信息

Magn Reson Med. 2009 May;61(5):1114-21. doi: 10.1002/mrm.21905.

Abstract

Fast large-angle spin echo (FLASE) is a common pulse sequence designed for quantitative imaging of trabecular bone (TB) microarchitecture. However, imperfections in the nonselective phase-reversal pulse render it prone to stimulated echo artifacts. The problem is further exacerbated at isotropic resolution. Here, a substantially improved RF-spoiled FLASE sequence (sp-FLASE) is described and its performance is illustrated with data at 1.5T and 3T. Additional enhancements include navigator echoes for translational motion sensing applied in a slice parallel to the imaging slab. Whereas recent work suggests the use of fully-balanced FLASE (b-FLASE) to be advantageous from a signal-to-noise ratio (SNR) point of view, evidence is provided here that the greater robustness of sp-FLASE may outweigh the benefits of the minor SNR gain of b-FLASE for the target application of TB imaging in the distal extremities, sites of exclusively fatty marrow. Results are supported by a theoretical Bloch equation analysis and the pulse sequence dependence of the effective T(2) of triglyceride protons. Last, sp-FLASE images are shown to provide detailed and reproducible visual depiction of trabecular networks in three dimensions at both anisotropic (137 x 137 x 410 microm(3)) and isotropic (160 x 160 x 160 microm(3)) resolutions in the human distal tibia in vivo.

摘要

快速大角度自旋回波(FLASE)是一种用于小梁骨(TB)微结构定量成像的常用脉冲序列。然而,非选择性相位反转脉冲的不完善使其容易产生受激回波伪影。在各向同性分辨率下,这个问题会进一步加剧。在此,描述了一种显著改进的射频扰相FLASE序列(sp-FLASE),并通过1.5T和3T的数据展示了其性能。额外的改进包括在与成像层面平行的切片中应用用于平移运动感知的导航回波。尽管最近的研究表明,从信噪比(SNR)的角度来看,使用完全平衡的FLASE(b-FLASE)具有优势,但本文提供的证据表明,对于四肢远端(仅含脂肪骨髓的部位)TB成像的目标应用,sp-FLASE更高的稳健性可能超过b-FLASE在小信噪比增益方面的优势。理论布洛赫方程分析以及甘油三酯质子有效T(2)的脉冲序列依赖性支持了这些结果。最后,sp-FLASE图像显示在体内人胫骨远端各向异性(137×137×410微米³)和各向同性(160×160×160微米³)分辨率下均能提供三维小梁网络的详细且可重复的视觉描绘。

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