Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908, USA.
Magn Reson Med. 2012 Jun;67(6):1730-9. doi: 10.1002/mrm.23139. Epub 2011 Aug 16.
Pancreatic β-cell imaging would be useful in monitoring the progression of and therapies for diabetes. The purpose of this study was to develop and evaluate quantitative β-cell MRI using manganese (Mn(2+)) labeling of β cells, T1 mapping, and a two-site water exchange model. Normal, pharmacologically-treated, and severely diabetic mice underwent injection of MnCl(2). Pancreatic water proton T1 relaxation was measured using Look-Locker MRI, and two-site water exchange analysis was used to estimate model parameters including the intracellular water proton relaxation rate constant (R1(ic)) and the intracellular fraction as indicators of β-cell function and mass, respectively. Logarithmic plots of T1 relaxation revealed two distinct proton pools relaxing with different T1s, and the two-site water exchange model fit the measured T1 relaxation data better than a monoexponential model. The intracellular R1(ic) time course revealed the kinetics of β-cell Mn(2+) labeling. Pharmacological treatments with nifedipine, tolbutamide, and diazoxide altered R1(ic), indicating that beta cell function was a determinant of Mn(2+) uptake. Intracellular fraction was significantly higher in mice with normal β cell mass than in diabetic mice (14.9% vs. 14.4%, P < 0.05). Two-site water exchange analysis of T1 relaxation of the Mn(2+)-enhanced pancreas is a promising method for quantifying β cell volume fraction and function.
胰腺β细胞成像是监测糖尿病进展和治疗的有用方法。本研究旨在开发和评估使用锰（Mn(2+)）标记β细胞、T1 映射和双位点水交换模型的定量β细胞 MRI。正常、药物治疗和严重糖尿病小鼠接受 MnCl(2)注射。使用 Look-Locker MRI 测量胰腺水质子 T1 弛豫，并用双位点水交换分析来估计模型参数，包括细胞内水质子弛豫率常数（R1(ic)）和细胞内分数，分别作为β细胞功能和质量的指标。T1 弛豫的对数图显示了两个具有不同 T1 的不同质子池，双位点水交换模型比单指数模型更能拟合测量的 T1 弛豫数据。细胞内 R1(ic)时间过程揭示了β细胞 Mn(2+)标记的动力学。硝苯地平、甲苯磺丁脲和二氮嗪的药物治疗改变了 R1(ic)，表明β细胞功能是 Mn(2+)摄取的决定因素。正常β细胞质量的小鼠的细胞内分数明显高于糖尿病小鼠（14.9%比 14.4%，P<0.05）。Mn(2+)增强胰腺 T1 弛豫的双位点水交换分析是定量β细胞体积分数和功能的有前途的方法。
