The Research Institute and Diagnostic Imaging, The Hospital for Sick Children, Toronto, Ontario, Canada.
Acad Radiol. 2011 Sep;18(9):1159-67. doi: 10.1016/j.acra.2011.04.016. Epub 2011 Jun 24.
Longitudinal (T(1)) and effective transverse (T(2)) magnetic resonance (MR) relaxation times provide noninvasive measures of tissue oxygenation. The objective for this study was to quantify independent effects of inhaled O(2) and CO(2) on normal tissue T(1) and T(2) in rabbit liver, kidney, and paraspinal muscle.
Three gas challenges (100% O(2), 10% CO(2) [balance air], and carbogen [90% O(2) + 10% CO(2)]) were delivered to the rabbits in random order to isolate the effects of inspired O(2) and CO(2). During each challenge, quantitative T(1) and T(2)* maps were collected on a 1.5 Tesla MR imaging. Mean changes in T(1) (ΔT(1)) and T(2)* (ΔT(2)*) were calculated from regions of interest in each organ.
Greatest ΔT(1) and ΔT(2)* changes were observed in liver for 10% CO(2) and in kidney for 100% O(2). ΔT(1) and ΔT(2)* generally followed predicted patterns when transitioning from air breathing: lower T(1)/higher T(2)* with inspired O(2), higher T(1)/lower T(2)* with inspired CO(2), and variable T(1)/T(2)* changes in the presence of both (ie, carbogen). New observations also emerged: 1) between-gas-challenge transitions revealed the greatest significance in ΔT(2)* for the liver and kidney resulting from the isolation of independent O(2) and CO(2) effects; 2) ΔT(2)* provided the best sensitivity and detected both tissue oxygenation and blood volume modulation; and 3) ΔT(1) sensitivity was restricted mainly to tissue oxygenation in the absence of counteracting vasodilatation.
Robust use of MR relaxation times as noninvasive biomarkers requires an understanding of their relative sensitivity to organ-specific physiological responses.
纵向弛豫时间（T(1)）和有效横向弛豫时间（T(2)*）磁共振（MR）弛豫时间提供了组织氧合的非侵入性测量。本研究的目的是量化吸入 O(2)和 CO(2)对正常兔肝、肾和脊柱旁肌肉 T(1)和 T(2)*的独立影响。
将三种气体挑战（100% O(2)、10% CO(2)[平衡空气]和碳氧合气[90% O(2)+10% CO(2)])以随机顺序输送到兔子体内，以分离吸入 O(2)和 CO(2)的影响。在每次挑战期间，在 1.5T MR 成像上采集定量 T(1)和 T(2)图谱。从每个器官的感兴趣区域计算 T(1)（ΔT(1)）和 T(2)（ΔT(2)*）的平均变化。
在肝组织中，10% CO(2)引起的ΔT(1)和 ΔT(2)*变化最大，在肾组织中，100% O(2)引起的ΔT(1)和 ΔT(2)*变化最大。当从空气呼吸过渡时，ΔT(1)和 ΔT(2)*通常遵循预测模式：吸入 O(2)时 T(1)/T(2)*升高，吸入 CO(2)时 T(1)/T(2)*降低，而同时存在 O(2)和 CO(2)时 T(1)/T(2)*变化（即碳氧合气）。还出现了新的观察结果：1）不同气体挑战之间的转变揭示了肝和肾组织中 ΔT(2)*的最大变化，这是由于 O(2)和 CO(2)的独立影响得到了分离；2）ΔT(2)*提供了最佳的敏感性，并检测到组织氧合和血容量调节；3）在没有拮抗血管扩张的情况下，ΔT(1)的敏感性主要局限于组织氧合。
磁共振弛豫时间作为非侵入性生物标志物的广泛应用需要了解它们对器官特异性生理反应的相对敏感性。
