Benefits and Pitfalls

It has been well reported in recent years that the accuracy of VFA T₁ estimates is very sensitive to pulse sequence implementations Baudrexel et al., 2017Lutti & Weiskopf, 2013Stikov et al., 2015, and as such is less robust than the gold standard inversion recovery technique. In particular, the signal bias resulting from insufficient spoiling can result in inaccurate T₁ estimates of up to 30% relative to inversion recovery estimated values Stikov et al., 2015. VFA T₁ map accuracy and precision is also strongly dependent on the quality of the measured B₁ map Lee et al., 2017, which can vary substantially between implementations Boudreau et al., 2017. Modern rapid B₁ mapping pulse sequences are not as widely available as VFA, resulting in some groups attempting alternative ways of removing the bias from the T₁ maps like generating an artificial B₁ map through the use of image processing techniques Liberman et al., 2013 or omitting B₁ correction altogether Yuan et al., 2012. The latter is not recommended, because most MRI scanners have default pulse sequences that, with careful protocol settings, can provide B₁ maps of sufficient quality very rapidly Boudreau et al., 2017Samson et al., 2006Wang et al., 2005.

Despite some drawbacks, VFA is still one of the most widely used T₁ mapping methods in research. Its rapid acquisition time, rapid image processing time, and widespread availability makes it a great candidate for use in other quantitative imaging acquisition protocols like quantitative magnetization transfer imaging Cercignani et al., 2005Yarnykh, 2002 and dynamic contrast enhanced imaging Li et al., 2018Sung et al., 2013.