Optimal echo times for multi-gradient echo-based B0 field-mapping.,NMR in Biomedicine

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Optimal echo times for multi-gradient echo-based B0 field-mapping.
NMR in Biomedicine ( IF 2.7 ) Pub Date : 2020-04-27 , DOI: 10.1002/nbm.4316
Yasmin Geiger ₁ , Assaf Tal ₁

Affiliation

B₀ field maps are used ubiquitously in neuroimaging, in disciplines ranging from magnetic resonance spectroscopy to temperature mapping and susceptibility‐weighted imaging. Most B₀ maps are acquired using standard gradient‐echo–based vendor‐provided sequences, often comprised of two echoes spaced a few milliseconds apart. Herein, we analyze the optimal spacing of echo times, defined as those maximizing precision—minimizing the standard deviation—for a fixed total acquisition time. Field estimation is carried out using a weighted least squares estimator. The standard deviation is shown to be approximately inversely proportional to the total acquisition time, suggesting a law of diminishing returns, whereby substantial gains are obtained up to a certain point, with little improvement beyond that point. Validations are provided in a phantom and a group of volunteers. Multi‐gradient echo sequences are readily available on all manufacturer platforms, making our recommendations straightforward to implement on any modern scanner.

中文翻译：

基于多梯度回波的 B0 场映射的最佳回波时间。

B ₀场图广泛用于神经成像，从磁共振波谱到温度映射和磁化率加权成像等学科。大多数 B ₀地图是使用标准的基于梯度回波的供应商提供的序列获取的，通常由间隔几毫秒的两个回波组成。在这里，我们分析了回波时间的最佳间隔，定义为在固定的总采集时间下最大化精度——最小化标准偏差。使用加权最小二乘估计器进行场估计。标准偏差与总采集时间大致成反比，表明存在收益递减规律，即在某一点之前获得大量收益，超过该点几乎没有改善。验证是在一个幻像和一组志愿者中提供的。多梯度回波序列可在所有制造商平台上轻松获得，使我们的建议可以直接在任何现代扫描仪上实施。

更新日期：2020-04-27

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