小儿脑肿瘤 T 弛豫时间的变化及其对代谢产物定量的影响。
Variation of T relaxation times in pediatric brain tumors and their effect on metabolite quantification.
机构信息
Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, West Midlands, UK.
Birmingham Children's Hospital NHS Foundation Trust, Birmingham, West Midlands, UK.
出版信息
J Magn Reson Imaging. 2019 Jan;49(1):195-203. doi: 10.1002/jmri.26054. Epub 2018 Apr 26.
BACKGROUND
Metabolite concentrations are fundamental biomarkers of disease and prognosis. Magnetic resonance spectroscopy (MRS) is a noninvasive method for measuring metabolite concentrations; however, quantitation is affected by T relaxation.
PURPOSE
To estimate T relaxation times in pediatric brain tumors and assess how variation in T relaxation affects metabolite quantification.
STUDY TYPE
Retrospective.
POPULATION
Twenty-seven pediatric brain tumor patients (n = 17 pilocytic astrocytoma and n = 10 medulloblastoma) and 24 age-matched normal controls.
FIELD STRENGTH/SEQUENCE: Short- (30 msec) and long-echo (135 msec) single-voxel MRS acquired at 1.5T.
ASSESSMENT
T relaxation times were estimated by fitting signal amplitudes at two echo times to a monoexponential decay function and were used to correct metabolite concentration estimates for relaxation effects.
STATISTICAL TESTS
One-way analysis of variance (ANOVA) on ranks were used to analyze the mean T relaxation times and metabolite concentrations for each tissue group and paired Mann-Whitney U-tests were performed.
RESULTS
The mean T relaxation of water was measured as 181 msec, 123 msec, 90 msec, and 86 msec in pilocytic astrocytomas, medulloblastomas, basal ganglia, and white matter, respectively. The T of water was significantly longer in both tumor groups than normal brain (P < 0.001) and in pilocytic astrocytomas compared with medulloblastomas (P < 0.01). The choline T relaxation time was significantly longer in medulloblastomas compared with pilocytic astrocytomas (P < 0.05), while the T relaxation time of NAA was significantly shorter in pilocytic astrocytomas compared with normal brain (P < 0.001). Overall, the metabolite concentrations were underestimated by ∼22% when default T values were used compared with case-specific T values at short echo time. The difference was reduced to 4% when individually measured water T s were used.
DATA CONCLUSION
Differences exist in water and metabolite T relaxation times for pediatric brain tumors, which lead to significant underestimation of metabolite concentrations when using default water T relaxation times.
LEVEL OF EVIDENCE
3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:195-203.
背景
代谢物浓度是疾病和预后的基本生物标志物。磁共振波谱（MRS）是一种测量代谢物浓度的非侵入性方法；然而，定量会受到 T 弛豫的影响。
目的
估计儿科脑肿瘤的 T 弛豫时间，并评估 T 弛豫变化如何影响代谢物定量。
研究类型
回顾性。
人群
27 名儿科脑肿瘤患者（n=17 例毛细胞星形细胞瘤和 n=10 例髓母细胞瘤）和 24 名年龄匹配的正常对照。
磁场强度/序列：在 1.5T 上采集短（30 毫秒）和长回波（135 毫秒）单体素 MRS。
评估
通过将两个回波时间的信号幅度拟合到单指数衰减函数来估计 T 弛豫时间，并使用该弛豫时间来校正代谢物浓度估计值。
统计检验
对每个组织组的平均 T 弛豫时间和代谢物浓度进行单因素方差分析（ANOVA），并进行配对 Mann-Whitney U 检验。
结果
在毛细胞星形细胞瘤、髓母细胞瘤、基底节和白质中，水的平均 T 弛豫时间分别为 181 毫秒、123 毫秒、90 毫秒和 86 毫秒。在肿瘤组中，水的 T 弛豫时间均明显长于正常脑（P<0.001），在毛细胞星形细胞瘤中明显长于髓母细胞瘤（P<0.01）。与毛细胞星形细胞瘤相比，髓母细胞瘤的胆碱 T 弛豫时间明显延长（P<0.05），而与正常脑相比，毛细胞星形细胞瘤的 NAA T 弛豫时间明显缩短（P<0.001）。总的来说，与短回波时间的特定于病例的 T 值相比，当使用默认 T 值时，代谢物浓度会低估约 22%。当单独测量水 T s 时，差异减少到 4%。
数据结论
儿科脑肿瘤的水和代谢物 T 弛豫时间存在差异，这导致当使用默认水 T 弛豫时间时，代谢物浓度会显著低估。
证据水平
3 技术功效：第 2 阶段 J. Magn. Reson. Imaging 2019;49:195-203.
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