Consideration of random errors in the quantitative imaging of NMR relaxation

Quantitative magnetic resonance imaging is a field whose development is at an early stage. Relatively little work has been done to assess the reliability of the values obtained from the quantitative maps previously presented. Here, the problem of spatial mapping of T₁ relaxation is studied. The effects of random errors on the results of imaging experiments incorporating saturation-recovery and fast inversion-recovery measurements are examined. Consideration is given to various factors affecting experimental design, common to all implementations of these techniques: the $\text{S}\text{N}$ ratio, the number of relaxation points sampled, and their distribution. No attempt has been made to assess different fitting algorithms. It is demonstrated that quantitative image data can be well modeled by simulations, leading to the conclusion that a T₁-imaging experiment can be regarded simply as a set of independentT₁ measurements, one on each image voxel. Results from previous work on bulk T₁ measurements are therefore applicable to quantitative imaging and are used to design an efficient imaging experiment, under a typical clinical time constraint of approximately one hour.