Goode S D, Krishan S, Alexakis C, Mahajan R, Auer D P
Department of Academic Radiology, Queens Medical Centre, Nottingham, UK.
AJNR Am J Neuroradiol. 2009 May;30(5):972-7. doi: 10.3174/ajnr.A1496.
Tools for noninvasive mapping of hemodynamic function including cerebrovascular reactivity are emerging and may become clinically useful to predict tissue at hemodynamic risk. One such technique assesses blood oxygen level-dependent (BOLD) MR imaging contrast in response to hypercapnia, but the reliability of its quantification is uncertain. The aim of this study was to prospectively investigate the intersubject and interhemispheric variability and short-term reproducibility of hypercapnia functional MR imaging (fMRI) in healthy volunteers and to assess the effects of different methods of quantification and normalization.
Sixteen healthy volunteers, (7 women and 9 men) underwent hypercapnia fMRI with a clinical 1.5T scanner; 8 underwent scanning twice. We determined BOLD amplitude changes using a visually defined block design or automated regression to end-tidal (ET) carbon dioxide (CO2). Absolute percent signal intensity changes (PSC) were extracted for whole-brain, gray matter, and middle cerebral artery territory, and also normalized to ETCO2 change. Intersubject and intrasubject (between hemispheres and sessions) coefficients of variation (COV) were derived. We assessed the effects of different quantification methods on reproducibility indices using the t test and U tests.
The mean change in ETCO2 was 7.8 +/- 3.3 mm Hg. Averaged BOLD increases varied from 2.54% to 2.92%. Short-term reproducibility was good for absolute PSC (4.8% to 10%) but poor for normalized PSC (range, 24% to 27% COV). Intersubject reproducibility varied between 11% and 23% for absolute PSC and, again, was poorer for normalized data (32% to 39%). Interhemispheric reproducibility of absolute PSC was excellent ranging between 1.24 and 2.16% COV.
In conclusion, quantification of cerebrovascular reactivity with use of hypercapnia fMRI was found to have good between-session and very good interhemispheric reproducibility. The technique holds promise as a diagnostic tool, especially for sensitive detection of unilateral disease.
用于血流动力学功能无创成像（包括脑血管反应性）的工具正在不断涌现，可能在临床上有助于预测处于血流动力学风险的组织。其中一种技术是评估对高碳酸血症反应的血氧水平依赖（BOLD）磁共振成像对比，但对其定量的可靠性尚不确定。本研究的目的是前瞻性地调查健康志愿者中高碳酸血症功能磁共振成像（fMRI）的受试者间和半球间变异性以及短期可重复性，并评估不同定量和归一化方法的影响。
16名健康志愿者（7名女性和9名男性）使用临床1.5T扫描仪进行高碳酸血症fMRI检查；其中8人进行了两次扫描。我们使用视觉定义的组块设计或自动回归到呼气末（ET）二氧化碳（CO2）来确定BOLD幅度变化。提取全脑、灰质和大脑中动脉区域的绝对信号强度变化百分比（PSC），并将其归一化到ETCO2变化。得出受试者间和受试者内（半球间和扫描间）变异系数（COV）。我们使用t检验和U检验评估不同定量方法对可重复性指标的影响。
ETCO2的平均变化为7.8±3.3 mmHg。平均BOLD增加范围为2.54%至2.92%。绝对PSC的短期可重复性良好（4.8%至10%），但归一化PSC的可重复性较差（COV范围为24%至27%）。绝对PSC的受试者间可重复性在11%至23%之间，同样，归一化数据的可重复性较差（32%至39%）。绝对PSC的半球间可重复性极佳，COV在1.24%至2.16%之间。
总之，发现使用高碳酸血症fMRI对脑血管反应性进行定量具有良好的扫描间和非常好的半球间可重复性。该技术有望成为一种诊断工具，特别是对于单侧疾病的敏感检测。
