Use of Ultrashort Echo Time MRI to Improve Skullbase Imaging

Introduction: Typically, the bone of the skullbase has appeared as a signal void on magnetic resonance (MR) imaging, making it impossible to differentiate from adjacent air. This is due to the short T2 nature of bone which forces clinicians to rely on computed tomography, with its ionizing radiation, to evaluate osseous structures. Through the use of novel MR sequences with ultra-short echo times (UTE), short T2 structures can now be visualized.

Methods: 8 patients (50% female) who were undergoing MR imaging of the skullbase for diagnostic purposes (62.5% for vestibular schwannoma surveillance), at a tertiary care center were prospectively enrolled over the year 2022 in a study evaluating UTE imaging. CT scans were completed in 50% of the patients as part of their workup. The repetition time, short echo time, and long echo time for the UTE sequence were 11 msec, 0.032 msec, and 2.2 msec respectively. The length of time for the UTE sequence was measured for each patient. All images were independently assessed by two neurotologists and a neuroradiologist.

Results: All patients tolerated the UTE sequence without issue. The protocol added only 6 minutes to the total scanning time compared to earlier published work which added 27 minutes. In all 8 patients, the ossicular chain was successfully identified and the trabeculations of the mastoid air cells along with the antrum were seen. In comparison to non-contrasted T1 weighted images, where healthy peripheral nerves are poorly seen, UTE allowed for clear delineation of all segments of the facial and cochlear nerves. The jugular bulb and sigmoid sinus were also visible. Lastly, vestibular schwannomas could be distinguished from normal brain parenchyma. Intriguingly, the tumor shape appeared larger on UTE than on contrasted T1 weighted images in a few patients.

Conclusions: UTE is safe and effective for visualizing structures not normally seen on traditional MRI, potentially allowing for improved surgical planning. Although UTE bone imaging is still currently inferior to CT, we anticipate that with additional refinement, such techniques will reduce the need for multimodality imaging in the future.