Analysis of the Precision of Variable Flip AngleT1Mapping with Emphasis on the Noise Propagated from RF Transmit Field Maps.
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 ofT1relaxation 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 forT1precision 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. Repeatedin vivoexperiments were performed to estimate the total variance inT1maps 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 theT1maps as either of the two SPGR images. Improving precision of the [Formula: see text] measurements significantly reduced the variance in the estimatedT1map. The variance estimated from the repeatedly measuredin vivoT1maps agreed well with the theoretically-calculated variance inT1estimates, thus validating the analytical framework for realisticin vivoexperiments. We concluded that forT1mapping 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 estimatedT1values.
Laboratory for Social and Neural Systems Research, University of ZürichZürich, Switzerland; Department of Information Technology and Electrical Engineering, Institute of Biomedical Engineering, ETH ZürichZürich, Switzerland.
Yoojin
Y
Lee
Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
Martina F
MF
Callaghan
Laboratory for Social and Neural Systems Research, University of ZürichZürich, Switzerland; Department of Information Technology and Electrical Engineering, Institute of Biomedical Engineering, ETH ZürichZürich, Switzerland.
Zoltan
Z
Nagy
B1+ map; T1 map; error propagation; precision; uncertainty; variable flip angle