Spence A M, Muzi M, Graham M M, O'Sullivan F, Krohn K A, Link J M, Lewellen T K, Lewellen B, Freeman S D, Berger M S, Ojemann G A
Department of Neurology, University of Washington School of Medicine, Seattle 98195, USA.
J Nucl Med. 1998 Mar;39(3):440-8.
Calculation of the glucose metabolic rate (MRGlc) in brain with PET and 2-[18F]fluoro-2-deoxy-D-glucose (FDG) requires knowing the rate of uptake of FDG relative to glucose from plasma into metabolite pools in the tissue. The proportionality factor for this is the FDG lumped constant (LC[FDG]), the ratio of the volumes of distribution of FDG and glucose multiplied by the hexokinase phosphorylation ratio for the two hexoses, Km(Glc) x Vm(FDG)/Km(FDG) x Vm(Glc) x MRGlc equals the FDG metabolic rate (MRFDG) divided by the LC(FDG), i.e., MRGlc = MRFDG/LC(FDG) and LC(FDG) = MRFDG/MRGlc. This investigation tested the hypothesis that LC(FDG) is significantly higher in gliomas than it is in brain uninvolved with tumor.
We imaged 40 patients with malignant gliomas with 1-[11C]glucose followed by FDG. The metabolic rates MRGlc and MRFDG were estimated for glioma and contralateral brain regions of interest by an optimization program based on three-compartment, four-rate constant models for the two hexoses.
The LC(FDG), estimated as MRFDG/MRGlc, in gliomas was 1.40 +/- 0.46 (mean +/- s.d.; range = 0.72-3.10), whereas in non-tumor-bearing contralateral brain, it was 0.86 +/- 0.14 (range = 0.61-1.21) (p < 0.001, glioma versus contralateral brain).
These data strongly suggest that the glioma LC(FDG) exceeds that of contralateral brain, that quantitation of the glioma MRGlc with FDG requires knowing the LC(FDG) specific for the glioma and that the LC(FDG) of normal brain is higher than previously reported estimates of about 0.50. 2-Fluoro-2-deoxy-D-glucose/PET studies in which glioma glucose metabolism is calculated by the autoradiographic approach with normal brain rate constants and LC(FDG) will overestimate glioma MRGlc, to the extent that the glioma LC(FDG) exceeds the normal brain LC(FDG). "Hot spots" visualized in FDG/PET studies of gliomas represent regions where MRGlc, LC(FDG) or their product is higher in glioma than it is in uninvolved brain tissue.
使用正电子发射断层扫描（PET）和2-[18F]氟-2-脱氧-D-葡萄糖（FDG）计算脑内葡萄糖代谢率（MRGlc）需要了解FDG从血浆进入组织代谢池的摄取率相对于葡萄糖摄取率的情况。其比例因子为FDG集总常数（LC[FDG]），即FDG与葡萄糖分布容积之比乘以两种己糖的己糖激酶磷酸化率，Km(Glc)×Vm(FDG)/Km(FDG)×Vm(Glc)×MRGlc等于FDG代谢率（MRFDG）除以LC(FDG)，即MRGlc = MRFDG/LC(FDG)且LC(FDG) = MRFDG/MRGlc。本研究检验了以下假设：胶质瘤中的LC(FDG)显著高于未受肿瘤累及的脑区。
我们对40例恶性胶质瘤患者先进行1-[11C]葡萄糖成像，随后进行FDG成像。通过基于两种己糖的三室、四速率常数模型的优化程序，估算胶质瘤和对侧脑感兴趣区域的代谢率MRGlc和MRFDG。
胶质瘤中以MRFDG/MRGlc估算的LC(FDG)为1.40±0.46（均值±标准差；范围 = 0.72 - 3.10），而在未患肿瘤的对侧脑区，其为0.86±0.14（范围 = 0.61 - 1.21）（p < 0.001，胶质瘤与对侧脑相比）。
这些数据有力地表明，胶质瘤的LC(FDG)超过对侧脑区，用FDG定量胶质瘤的MRGlc需要了解胶质瘤特异性的LC(FDG)，且正常脑的LC(FDG)高于先前报道的约0.50的估计值。在通过自显影方法并使用正常脑速率常数和LC(FDG)来计算胶质瘤葡萄糖代谢的2-氟-2-脱氧-D-葡萄糖/PET研究中，会高估胶质瘤的MRGlc，高估程度取决于胶质瘤的LC(FDG)超过正常脑LC(FDG)的程度。在胶质瘤的FDG/PET研究中显示的“热点”代表了胶质瘤中MRGlc、LC(FDG)或其乘积高于未受累脑组织的区域。
