Kjaer L, Thomsen C, Larsson H B, Henriksen O, Ring P
Department of Magnetic Resonance, Hvidovre Hospital, University of Copenhagen, Denmark.
Acta Radiol. 1988 Jul-Aug;29(4):473-9.
Despite the complexity of biologic tissues, a monoexponential behaviour is usually assumed when estimating relaxation processes in vivo by magnetic resonance imaging (MRI). This study was designed to evaluate the potential of biexponential decomposition of T1 and T2 relaxation curves obtained at 1.5 tesla (T). Measurements were performed on a phantom of bicompartmental perspex boxes with combinations of different CuSO4 concentrations. T1 determination was based on a 12-points partial saturation inversion recovery pulse sequence. T2 determination was provided by a multiple spin echo sequence with 32 echoes. Applying biexponential curve analysis, a significant deviation from a monoexponential behaviour was recognized at a ratio of corresponding relaxation rates of about 3 and 2, estimating T1 and T2 relaxation, respectively (p less than 0.01, F-test). Requiring an SD less than or equal to 10 per cent for each set of parameters, the biexponential model was accepted when this ratio exceeded a factor of 5 and 8, respectively. Referring to 'expected' T1 and T2 values, however, an accuracy within 20 per cent only was observed at ratios of at least 6 and 15. It is concluded that quantitative estimation of individual and specific relaxation components in complex biologic tissues by MRI may prove very difficult.
尽管生物组织具有复杂性，但在通过磁共振成像（MRI）对体内弛豫过程进行估计时，通常假定为单指数行为。本研究旨在评估在1.5特斯拉（T）下获得的T1和T2弛豫曲线双指数分解的潜力。测量是在具有不同硫酸铜浓度组合的双隔室有机玻璃盒体模上进行的。T1的测定基于一个12点的部分饱和反转恢复脉冲序列。T2的测定由一个具有32个回波的多自旋回波序列提供。应用双指数曲线分析，在相应弛豫率之比约为3和2时，分别估计T1和T2弛豫，发现与单指数行为存在显著偏差（p小于0.01，F检验）。对于每组参数，要求标准差小于或等于10%，当该比率分别超过5倍和8倍时，双指数模型被接受。然而，参考“预期”的T1和T2值，仅在比率至少为6和15时观察到20%以内的准确度。得出的结论是，通过MRI对复杂生物组织中的个体和特定弛豫成分进行定量估计可能非常困难。
