Rodgers Zachary B, Englund Erin K, Langham Michael C, Magland Jeremy F, Wehrli Felix W
Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
Neuroimage. 2015 Feb 1;106:441-50. doi: 10.1016/j.neuroimage.2014.10.061. Epub 2014 Nov 4.
Susceptometry-based oximetry (SBO) and T2-relaxation-under-spin-tagging (TRUST) are two promising methods for quantifying the cerebral metabolic rate of oxygen (CMRO2), a critical parameter of brain function. We present a combined method, interleaved TRUST (iTRUST), which achieves rapid, simultaneous quantification of both susceptometry- and T2-based CMRO2 via insertion of a flow-encoded, dual-echo gradient-recalled echo (OxFlow) module within the T1 recovery portion of the TRUST sequence. In addition to allowing direct comparison between SBO- and TRUST-derived venous oxygen saturation (Yv) values, iTRUST substantially improves TRUST temporal resolution for CMRO2 quantification and obviates the need for a separate blood flow measurement following TRUST acquisition. iTRUST was compared directly to TRUST and OxFlow alone in three resting subjects at baseline, exhibiting close agreement with the separate techniques and comparable precision. These baseline data as well as simulation results support the use of two instead of the traditional four T2 preparation times for T2 fitting, allowing simultaneous quantification of susceptometry- and T2-based Yv (and CMRO2) with three- and six-second temporal resolution, respectively. In 10 young healthy subjects, iTRUST was applied during a 5% CO2 gas mixture-breathing paradigm. T2-based Yv values were lower at baseline relative to susceptometry (62.3 ± 3.1 vs. 66.7 ± 5.1 %HbO2, P<0.05), but increased more in response to hypercapnia. As a result, T2-based CMRO2 decreased from 140.4 ± 9.7 to 120.0 ± 9.5 μMol/100g/min, a significant -14.6 ± 3.6% response (P < 0.0001), whereas susceptometry-based CMRO2 changed insignificantly from 123.4 ± 18.7 to 127.9 ± 25.7, a 3.3 ± 9.7% response (P = 0.31). These differing results are in accord with previous studies applying the parent OxFlow or TRUST sequences individually, thus supporting the reliability of iTRUST but also strongly suggesting that a systematic bias exists between the susceptometry- and T2-based Yv quantification techniques.
基于磁化率测量的血氧测定法（SBO）和自旋标记下的T2弛豫法（TRUST）是两种很有前景的用于量化脑氧代谢率（CMRO2）的方法，脑氧代谢率是脑功能的一个关键参数。我们提出了一种组合方法，即交错TRUST（iTRUST），通过在TRUST序列的T1恢复部分插入一个流动编码的双回波梯度回波（OxFlow）模块，实现了基于磁化率测量和基于T2的CMRO2的快速、同时量化。除了能够直接比较基于SBO和TRUST得出的静脉血氧饱和度（Yv）值外，iTRUST还显著提高了用于CMRO2量化的TRUST时间分辨率，并且无需在TRUST采集后单独进行血流测量。在三名静息状态的受试者基线期将iTRUST直接与单独的TRUST和OxFlow进行比较，结果显示与单独的技术结果高度一致且精度相当。这些基线数据以及模拟结果支持在T2拟合中使用两个而非传统的四个T2准备时间，从而能够分别以三秒和六秒的时间分辨率同时量化基于磁化率测量和基于T2的Yv（以及CMRO2）。在10名年轻健康受试者中，在吸入5%二氧化碳混合气体的范式期间应用了iTRUST。基于T2的Yv值在基线期相对于基于磁化率测量的值较低（62.3±3.1对66.7±5.1%HbO2，P<0.05），但对高碳酸血症的反应增加更多。结果，基于T2的CMRO2从140.4±9.7降至120.0±9.5μMol/100g/min，有显著的-14.6±3.6%的反应（P<0.0001），而基于磁化率测量的CMRO2从123.4±18.7至127.9±25.7变化不显著，有3.3±9.7%的反应（P = 0.31）。这些不同的结果与之前分别应用原始OxFlow或TRUST序列的研究一致，因此支持了iTRUST的可靠性，但也强烈表明在基于磁化率测量和基于T2的Yv量化技术之间存在系统偏差。
