Comparison of the detectability of UBOs in Neurofibromatosis Type I patients with proton density-weighted and FLAIR sequences in 3T MRI

Objective

In NF 1 patients, significant numbers of so-called unidentified bright objects (UBOs) can be found. The aim of the study was to investigate whether the detectability of UBOs increases at 3T by comparing Proton density-weighted images (PDw) with fluid-attenuated inversion recovery (FLAIR) sequences.

Patients and methods

A total of 14 NF1 patients (7 male, 7 female, between 8 and 26 years old, mean age 15.4 years) were examined by a 3T magnetic resonance scanner. The presence of UBOs was evaluated on PD-w and FLAIR images by 4 evaluators. Detectability was rated by a three-point scoring system: lesions which were “well defined/detectable”, “suspicious” or “detected after a second look”. The Wilcoxon signed-rank test was used for comparisons between the raters. The level of significance was P < 0.05.

Results

Significantly more lesions were marked as “well defined/detectable” in the PD-w Sequence compared to FLAIR at 3T (P < 0.001 for all four evaluators together, as well as for each evaluator separately). In particular, PD-w proved to be superior for detecting UBOs located in the medulla oblongata, dentate nucleus and hippocampal region, regardless of the level of the raters' experience.

Conclusion

This is the first study which compares FLAIR and PD-w at 3T for the diagnosis of UBOs in NF1. At this field strength significantly more UBOs were detected in the PD-w compared to FLAIR sequences, especially for the infratentorial regions. As UBOs occur at very early stages of the disease in patients with suspected NF1, PD-w might aid in the early diagnosis when using 3T scanners.