Guivel-Scharen V, Sinnwell T, Wolff S D, Balaban R S
Laboratory of Cardiac Energetics, National Heart Lung and Blood Institute, Bldg. 10, Bethesda, Maryland, 20892-1061, USA.
J Magn Reson. 1998 Jul;133(1):36-45. doi: 10.1006/jmre.1998.1440.
Metabolites in proton chemical exchange with water were detected via the water proton signal using saturation transfer techniques in model systems and biological tissues. The metabolites were selectively saturated and the resulting decrease in the much larger water proton pool was used to monitor the metabolite. This indirect detection scheme can result in a several orders of magnitude increase in sensitivity for metabolites over direct detection methods. A control irradiation scheme was devised to compensate for macromolecular/water magnetization transfer. Using this approach, significant chemical exchange regions at approximately 1 and 2.5 ppm were detected in kidney medulla. Using a difference imaging technique between a control irradiation above (-1.74 ppm) and below (+1.74 ppm) the water resonance, a chemical exchange image of the kidney was calculated. These data revealed a linear gradient of chemical exchange increasing from the cortex to the medulla. Studies on medullary acid extracts and urine revealed that the exchange observed in the kidney was predominantly with low molecular weight metabolites. Urea (1 ppm) was identified as contributing to the kidney/urine chemical exchange; however, other unidentified metabolites may also contribute to this effect. These studies demonstrate that tissue metabolites can be detected and imaged via the water protons using the signal amplification properties of saturation transfer in the presence of water/macromolecule magnetization transfer.
在模型系统和生物组织中，利用饱和转移技术通过水质子信号检测与水发生质子化学交换的代谢物。代谢物被选择性地饱和，然后利用大得多的水质子池的信号下降来监测代谢物。这种间接检测方案相较于直接检测方法，可使代谢物的灵敏度提高几个数量级。设计了一种对照照射方案来补偿大分子/水的磁化转移。采用这种方法，在肾髓质中检测到了大约1 ppm和2.5 ppm处的显著化学交换区域。利用水共振上方（-1.74 ppm）和下方（+1.74 ppm）的对照照射之间的差异成像技术，计算出了肾脏的化学交换图像。这些数据揭示了从皮质到髓质化学交换呈线性梯度增加。对髓质酸提取物和尿液的研究表明，在肾脏中观察到的交换主要是与低分子量代谢物发生的。已确定尿素（1 ppm）是肾脏/尿液化学交换的原因之一；然而，其他未鉴定的代谢物也可能导致这种效应。这些研究表明，在存在水/大分子磁化转移的情况下，利用饱和转移的信号放大特性，可通过水质子检测和成像组织代谢物。
