Uncertainty and bias in contrast concentration measurements using spoiled gradient echo pulse sequences
Uncertainty and bias in contrast concentration measurements using spoiled gradient echo pulse sequences
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DOI：
10.1088/0031-9155/53/9/010
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发表时间：
2008-05-07
影响因子：
3.5
通讯作者：
Parker, Dennis L.
中科院分区：
文献类型：
--
作者：
Schabel, Matthias C.;Parker, Dennis L.
动态对比增强磁共振成像（DCE-MRI）是一种广泛使用的评估组织生理学的技术。破坏梯度回波 (SPGR) 脉冲序列是采集 DCE-MRI 数据的最常用方法之一，可通过强大的 T-1 加权提供高时间和空间分辨率。简要回顾了 SPGR 信号到浓度的转换，并推导了有限信噪比 (SNR) 和基线扫描时间的浓度测量不确定度的新封闭式表达式。该结果适用于任意浓度依赖性弛豫率，并且在与理论 SPGR 信号方程相同的域内有效。还导出了可测量浓度的下限和上限的表达式。证明了浓度和组织相关的最佳翻转角的存在，该最佳翻转角可以最小化浓度不确定性，并且表明，对于临床相关的脉冲序列参数，该最佳翻转角明显大于相应的恩斯特角。对 DCE-MRI 文献中的三个脉冲序列的分析表明，使用此处讨论的方法优化翻转角可在 0.5-5.0 mM 浓度范围内将有效 SNR 潜在提高 10-1166%，同时测量精度损失最小或无损失，低至 0.1 mM。来自三名研究患者的体内数据为我们对浓度测量不确定性的理论表达提供了进一步的支持，预测和实验估计值一致在 +/- 30% 范围内。由翻转角偏差以及对比前弛豫时间和对比弛豫率（纵向和横向）产生的浓度偏差方程也以封闭形式导出。由此产生的方程表明，即使翻转角和/或对比前纵向弛豫时间的相对较小的错误指定，特别是在高对比浓度下，也可能对浓度测量的偏差产生重大影响。
Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a widely used technique for assessing tissue physiology. Spoiled gradient echo (SPGR) pulse sequences are one of the most common methods for acquisition of DCE-MRI data, providing high temporal and spatial resolution with strong T-1-weighting. Conversion of SPGR signal to concentration is briefly reviewed, and a new closed-form expression for concentration measurement uncertainty for finite signal-to-noise ratio (SNR) and baseline scan time is derived. This result is applicable to arbitrary concentration-dependent relaxation rate and is valid over the same domain as the theoretical SPGR signal equation. Expressions for the lower and upper bounds on measurable concentration are also derived. The existence of a concentration- and tissue-dependent optimal flip angle that minimizes concentration uncertainty is demonstrated and it is shown that, for clinically relevant pulse sequence parameters, this optimal flip angle is significantly larger than the corresponding Ernst angle. Analysis of three pulse sequences from the DCE-MRI literature shows that optimization of flip angle using the methods discussed here leads to potential improvements of 10-1166% in effective SNR over the 0.5-5.0 mM concentration range with minimal or no loss of measurement accuracy down to 0.1 mM. In vivo data from three study patients provide further support for our theoretical expression for concentration measurement uncertainty, with predicted and experimental estimates agreeing to within +/- 30%. Equations for concentration bias resulting from biases in flip angle and from pre-contrast relaxation time and contrast relaxivity ( both longitudinal and transverse) are also derived in closed-form. The resulting equations show the potential for significant contributions to bias in concentration measurement arising from even relatively small mis-specification of flip angle and/or pre-contrast longitudinal relaxation time, particularly at high contrast concentrations.