Assessment of Silent T1-weighted head imaging at 7 T.

Objectives: This study aimed to assess the performance of a "Silent" zero time of echo (ZTE) sequence for T1-weighted brain imaging using a 7 T MRI system.

Methods: The Silent sequence was evaluated qualitatively by two neuroradiologists, as well as quantitatively in terms of tissue contrast, homogeneity, signal-to-noise ratio (SNR) and acoustic noise. It was compared to conventional T1-weighted imaging (FSPGR). Adequacy for automated segmentation was evaluated in comparison with FSPGR acquired at 7 T and 1.5 T. Specific absorption rate (SAR) was also measured.

Results: Tissue contrast and homogeneity in Silent were remarkable in deep brain structures and in the occipital and temporal lobes. Mean tissue contrast was significantly (p < 0.002) higher in Silent (0.25) than in FSPGR (0.11), which favoured automated tissue segmentation. On the other hand, Silent images had lower SNR with respect to conventional imaging: average SNR of FSPGR was 2.66 times that of Silent. Silent images were affected by artefacts related to projection reconstruction, which nevertheless did not compromise the depiction of brain tissues. Silent acquisition was 35 dB(A) quieter than FSPGR and less than 2.5 dB(A) louder than ambient noise. Six-minute average SAR was <2 W/kg.

Conclusions: The ZTE Silent sequence provides high-contrast T1-weighted imaging with low acoustic noise at 7 T.

Key Points: • "Silent" is an MRI technique allowing zero time of echo acquisition • Its feasibility and performance were assessed on a 7 T MRI system • Image quality in several regions was higher than in conventional techniques • Imaging acoustic noise was dramatically reduced compared with conventional imaging • "Silent" is suitable for T1-weighted head imaging at 7 T.