在3特斯拉磁场下使用时间级联脉冲对人脑进行三维哈达玛编码质子光谱成像。

Three-dimensional Hadamard-encoded proton spectroscopic imaging in the human brain using time-cascaded pulses at 3 Tesla.

作者信息

Cohen Ouri, Tal Assaf, Gonen Oded

机构信息

Department of Radiology, New York University, New York, New York, USA; Biomedical Engineering, Columbia University, New York, New York, USA.

出版信息

Magn Reson Med. 2014 Oct;72(4):923-33. doi: 10.1002/mrm.25022. Epub 2013 Nov 20.

DOI:10.1002/mrm.25022

PMID:24259447

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC4028436/

Abstract

PURPOSE

To reduce the specific-absorption-rate (SAR) and chemical shift displacement (CSD) of three-dimensional (3D) Hadamard spectroscopic imaging (HSI) and maintain its point spread function (PSF) benefits.

METHODS

A 3D hybrid of 2D longitudinal, 1D transverse HSI (L-HSI, T-HSI) sequence is introduced and demonstrated in a phantom and the human brain at 3 Tesla (T). Instead of superimposing each of the selective Hadamard radiofrequency (RF) pulses with its N single-slice components, they are cascaded in time, allowing N-fold stronger gradients, reducing the CSD. A spatially refocusing 180° RF pulse following the T-HSI encoding block provides variable, arbitrary echo time (TE) to eliminate undesirable short T2 species' signals, e.g., lipids.

RESULTS

The sequence yields 10-15% better signal-to-noise ratio (SNR) and 8-16% less signal bleed than 3D chemical shift imaging of equal repetition time, spatial resolution and grid size. The 13 ± 6, 22 ± 7, 24 ± 8, and 31 ± 14 in vivo SNRs for myo-inositol, choline, creatine, and N-acetylaspartate were obtained in 21 min from 1 cm(3) voxels at TE ≈ 20 ms. Maximum CSD was 0.3 mm/ppm in each direction.

CONCLUSION

The new hybrid HSI sequence offers a better localized PSF at reduced CSD and SAR at 3T. The short and variable TE permits acquisition of short T2 and J-coupled metabolites with higher SNR.

摘要

目的

降低三维（3D）哈达玛光谱成像（HSI）的比吸收率（SAR）和化学位移偏移（CSD），并保持其点扩散函数（PSF）优势。

方法

引入一种二维纵向、一维横向HSI（L-HSI、T-HSI）序列的3D混合序列，并在体模和3特斯拉（T）的人脑模型中进行了演示。不是将每个选择性哈达玛射频（RF）脉冲与其N个单层分量叠加，而是在时间上进行级联，允许N倍更强的梯度，从而降低CSD。在T-HSI编码块之后的空间重聚焦180°RF脉冲提供可变的、任意的回波时间（TE），以消除不需要的短T2物质（如脂质）的信号。

结果

与具有相同重复时间、空间分辨率和网格大小的3D化学位移成像相比，该序列的信噪比（SNR）提高了10-15%，信号泄漏减少了8-16%。在TE≈20 ms时，从1 cm³体素中在21分钟内获得了肌醇、胆碱、肌酸和N-乙酰天门冬氨酸的体内SNR分别为13±6、22±7、24±8和31±14。每个方向上的最大CSD为0.3 mm/ppm。