Disappearance of multiple sclerosis lesions with severely prolonged T1 on images obtained by a FLAIR pulse sequence.

Although the superiority of FLAIR over conventional T2-weighted spin-echo (SE) is still unclear, one potential advantage would be its use in quantitative lesion load measurements. We have observed a potential pitfall regarding the use of FLAIR in image quantification. We report a case where a part of the hyperintense lesions on T2 SE, which was hypointense on T1 SE, subsequently was found to be isointense to brain on FLAIR images. Therefore, quantification of lesion load by means of FLAIR might underestimate the "true" lesion load, as seen on T2 SE.