Analysis of the Precision of Variable Flip Angle T₁ Mapping with Emphasis on the Noise Propagated from RF Transmit...

In magnetic resonance imaging, precise measurements of longitudinal relaxation time (T₁) is crucial to acquire useful information that is applicable to numerous clinical and neuroscience applications. In this work, we investigated the precision of T₁ relaxation time as measured using the variable flip angle method with emphasis on the noise propagated from radiofrequency transmit field ([Formula: see text]) measurements. The analytical solution for T₁ precision was derived by standard error propagation methods incorporating the noise from the three input sources: two spoiled gradient echo (SPGR) images and a [Formula: see text] map. Repeated in vivo experiments were performed to estimate the total variance in T₁ maps and we compared these experimentally obtained values with the theoretical predictions to validate the established theoretical framework. Both the analytical and experimental results showed that variance in the [Formula: see text] map propagated comparable noise levels into the T₁ maps as either of the two SPGR images. Improving precision of the [Formula: see text] measurements significantly reduced the variance in the estimated T₁ map. The variance estimated from the repeatedly measured in vivoT₁ maps agreed well with the theoretically-calculated variance in T₁ estimates, thus validating the analytical framework for realistic in vivo experiments. We concluded that for T₁ mapping experiments, the error propagated from the [Formula: see text] map must be considered. Optimizing the SPGR signals while neglecting to improve the precision of the [Formula: see text] map may result in grossly overestimating the precision of the estimated T₁ values.