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.