The Research Institute and Diagnostic Imaging, The Hospital for Sick Children, Toronto, Canada.
Phys Med Biol. 2011 Mar 7;56(5):1225-42. doi: 10.1088/0031-9155/56/5/001. Epub 2011 Feb 1.
Magnetic resonance imaging (MRI) relaxation times provide indirect estimates of tissue O(2) for monitoring tumour oxygenation. This study provides insight into mechanisms underlying longitudinal (R(1) = 1/T(1)) and transverse effective (R(2)* = 1/T(2)) relaxation rate changes during inhalation of 100% O(2) and 3%, 6% and 9% CO(2) (balanced O(2)) in a rabbit tumour model. Quantitative R(1), R(2), and dynamic contrast-enhanced (DCE) imaging was performed in six rabbits 12-23 days following implantation of VX2 carcinoma cells in the quadricep muscle. Invasive measurements of tissue partial pressure of O(2) (pO(2)) and perfusion were also performed, which revealed elevated pO(2) levels in all tumour regions for all hyperoxic gases compared to baseline (air) and reduced perfusion for carbogen. During 100% O(2) breathing, an R(1) increase and R(2)* decrease consistent with elevated pO(2) were observed within tumours. DCE-derived blood flow was weakly correlated with R(1) changes from air to 100% O(2). Further addition of CO(2) (carbogen) did not introduce considerable changes in MR relaxation rates, but a trend towards higher R(1) relative to breathing 100% O(2) was observed, while R(2)* changes were inconsistent. This observation supports the predominance of dissolved O(2) on R(1) sensitivity and demonstrates the value of R(1) over R(2)* for tissue oxygenation measures.
磁共振成像（MRI）弛豫时间提供了组织氧的间接估计，用于监测肿瘤氧合。本研究深入了解了在兔子肿瘤模型中吸入 100%O2 和 3%、6%和 9%CO2（平衡 O2）时纵向（R1=1/T1）和横向有效（R2*=1/T2*）弛豫率变化的机制。在 VX2 癌细胞植入股四头肌 12-23 天后，对六只兔子进行了定量 R1、R2和动态对比增强（DCE）成像。还进行了组织氧分压（pO2）和灌注的侵入性测量，结果显示与基线（空气）相比，所有高氧气体都使所有肿瘤区域的 pO2 水平升高，而碳化氧合作用则降低了灌注。在 100%O2 呼吸期间，在肿瘤内观察到与升高的 pO2 一致的 R1 增加和 R2减少。DCE 衍生的血流与从空气到 100%O2 的 R1 变化弱相关。进一步添加 CO2（碳化氧合）不会导致 MR 弛豫率发生明显变化，但观察到与呼吸 100%O2 相比，R1 相对升高的趋势，而 R2变化不一致。这一观察结果支持溶解氧对 R1 敏感性的主导作用，并证明了 R1 用于组织氧合测量的价值超过 R2。
