Carson R E, Channing M A, Blasberg R G, Dunn B B, Cohen R M, Rice K C, Herscovitch P
Positron Emission Tomography Department, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
J Cereb Blood Flow Metab. 1993 Jan;13(1):24-42. doi: 10.1038/jcbfm.1993.6.
Positron emission tomography studies with the opiate antagonist [18F]cyclofoxy ([18F]CF) were performed in baboons. Bolus injection studies demonstrated initial uptake dependent on blood flow. The late uptake showed highest binding in caudate nuclei, amygdala, thalamus, and brainstem and the least accumulation in cerebellum. By 60 min postinjection, regional brain radioactivity cleared at the same rate as metabolite-corrected plasma, i.e., transient equilibrium was achieved. Compartmental modeling methods were applied to time-activity curves from brain and metabolite-corrected plasma. Individual rate constants were estimated with poor precision. The model estimate of the total volume of distribution (VT), representing the ratio of tissue radioactivity to metabolite-corrected plasma at equilibrium, was reliably determined. The apparent volume of distribution (Va), the concentration ratio of tissue to metabolite-corrected plasma during transient equilibrium, was compared with the fitted VT values to determine if single-scan methods could provide accurate receptor measurements. Va significantly overestimated VT and produced artificially high image contrast. These differences were predicted by compartment model theory and were caused by a plasma clearance rate that was close to the slowest tissue clearance rate. To develop a simple method to measure VT, an infusion protocol consisting of bolus plus continuous infusion (B/I) of CF was designed and applied in a separate set of studies. The Va values from the B/I studies agreed with the VT values from both B/I and bolus studies. This infusion approach can produce accurate receptor measurements and has the potential to shorten scan time and simplify the acquisition and processing of scan and blood data.
用阿片类拮抗剂[18F]环福昔（[18F]CF）对狒狒进行了正电子发射断层扫描研究。团注注射研究表明，初始摄取依赖于血流。晚期摄取在尾状核、杏仁核、丘脑和脑干中显示出最高的结合，而在小脑中的积累最少。注射后60分钟，脑区放射性以与代谢物校正血浆相同的速率清除，即达到了瞬态平衡。将房室模型方法应用于脑和代谢物校正血浆的时间-活性曲线。个体速率常数的估计精度较差。可靠地确定了代表平衡时组织放射性与代谢物校正血浆之比的分布总体积（VT）的模型估计值。比较了瞬态平衡期间组织与代谢物校正血浆的浓度比——表观分布容积（Va）与拟合的VT值，以确定单扫描方法是否能提供准确的受体测量值。Va显著高估了VT，并产生了人为的高图像对比度。这些差异由房室模型理论预测，是由接近最慢组织清除率的血浆清除率引起的。为了开发一种测量VT的简单方法，设计了一种由CF团注加持续输注（B/I）组成的输注方案，并应用于另一组研究中。B/I研究中的Va值与B/I和团注研究中的VT值一致。这种输注方法可以产生准确的受体测量值，并且有可能缩短扫描时间，简化扫描和血液数据的采集与处理。
