Reply to the Letter to the Editor: “Visualization of the saccule and utricle with non-contrast-enhanced FLAIR sequences”

by Hikaru Fukutomi and Thomas Tourdias (thomas.tourdias@chu-bordeaux.fr)

Visualization of the saccule and utricle with non-contrast-enhanced FLAIR sequences

Dear Editor-in-Chief,

We thank Dr. Eliezer for his comments on our article. We fully agree with Dr. Eliezer that the formal validation will require a direct comparison of the non-contrast method optimized here [1] with the standard post-gadolinium method. At this stage, we tried to identify the best combination of MR parameters that could capture differences of relaxation times that are likely to exist between the endo- and the perilymphatic spaces. We relied on expected anatomical disposition of utricle and saccule in this first step.

It is interesting to read that Dr. Eliezer’s group has unpublished data pointing toward identical T1 values between endo- and perilymphatic spaces which is in lines with our conclusion and with the need to enhance T2 contrast as we did with a long T2-prep module.

We agree with Dr. Eliezer that separation of the structures is however still challenging even with the T2-prep module because sequence optimization in MR is always based on tradeoffs. It is true that, in order to capture the thin band of perilymph between utricle and saccule, it is better to favor higher signal which is balanced by lower contrast. This is exactly what we concluded by pointing toward a TI that is higher than the nulling point of endolymphatic space in order to get more signal even though the counterpart might be imperfect nulling of some part of the endolymphatic space [1]. We will be happy to provide Dr. Eliezer full series of images upon request.

Now, the method that we have optimized is therefore to be evaluated for its clinical performances against delayed images after gadolinium injection. We don’t expect to replace the reference-standard gadolinium method for all the patients but we might be able to demonstrate a place for such a non-gadolinium method in a triage algorithm.