Nishizawa S, Leyton M, Okazawa H, Benkelfat C, Mzengeza S, Diksic M
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Quebec, Canada.
J Cereb Blood Flow Metab. 1998 Oct;18(10):1121-9. doi: 10.1097/00004647-199810000-00009.
We tested in normal human subjects a less invasive method to obtain plasma input function required in the calculation of the brain serotonin synthesis rate measured with positron emission tomography (PET) and alpha-[11C]methyl-tryptophan (alpha-MTrp). The synthesis rates derived with the arterial input function were compared to those derived from venous plasma and venous sinus time-radioactivity curves obtained from dynamic PET images. Dynamic PET images were obtained for the lengths up to 90 minutes after an injection of alpha-MTrp (400 to 800 MBq). Input functions were generated from both artery and vein in three subjects, and from artery only in two subjects. Net unidirectional uptake constants of alpha-MTrp (K*; mL/g/min) were calculated in several brain regions graphically using data between 20 and 60 minutes after injection with different input functions. In the five subjects with arterial sampling, we tested two methods for correcting the input functions from the venous samples: (1) normalization to the mean exposure time at 20 minutes from arterial curve; and (2) the use of the venous sinus curve for the first 20 minutes. Venous curves coincided with the arterial ones after about 20 minutes. When the venous curves were used, there was an underestimation of the area under the curves up to 20 minutes, resulting in a 5% to 30% overestimation of K* values. Combined use of the sinus curve up to 20 minutes and venous curve from 20 to 60 minutes as an input function resulted in the K* (mL/g/min) values larger by 7.1 +/- 3.8% than the K* values estimated with the arterial input function. Normalization of the venous curve to the exposure time at 20 minutes obtained from the arterial plasma curve resulted in a bias in the K* of about -0.34 +/- 3.32%. The bias from the K* values was propagated to the serotonin synthesis rates. The use of a combination of the venous blood samples and venous sinus as the input function resulted in an acceptable bias in the serotonin synthesis rates from the tissue time-radioactivity curves generated by PET.
我们在正常人体受试者中测试了一种侵入性较小的方法，以获取正电子发射断层扫描（PET）和α-[¹¹C]甲基色氨酸（α-MTrp）测量脑血清素合成率时所需的血浆输入函数。将通过动脉输入函数得出的合成率与从动态PET图像获得的静脉血浆和静脉窦时间-放射性曲线得出的合成率进行比较。在注射α-MTrp（400至800 MBq）后长达90分钟的时间内获取动态PET图像。在三名受试者中从动脉和静脉生成输入函数，在两名受试者中仅从动脉生成输入函数。使用注射后20至60分钟之间的数据，以图形方式计算了几个脑区中α-MTrp的净单向摄取常数（K*；mL/g/min），使用了不同的输入函数。在进行动脉采样的五名受试者中，我们测试了两种校正静脉样本输入函数的方法：（1）根据动脉曲线在20分钟时的平均暴露时间进行归一化；（2）在前20分钟使用静脉窦曲线。大约20分钟后，静脉曲线与动脉曲线重合。当使用静脉曲线时，曲线下面积在20分钟之前被低估，导致K值高估5%至30%。将窦曲线前20分钟和静脉曲线20至60分钟组合用作输入函数，得出的K（mL/g/min）值比用动脉输入函数估计的K值大7.1±3.8%。将静脉曲线根据从动脉血浆曲线获得的20分钟时的暴露时间进行归一化，导致K偏差约为-0.34±3.32%。K*值的偏差传播到血清素合成率。将静脉血样本和静脉窦组合用作输入函数，导致PET生成的组织时间-放射性曲线得出的血清素合成率存在可接受的偏差。
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