Abstract
The pointwise encoding time reduction with radial acquisition (PETRA) ultrashort echo time MR imaging sequence at 3T enables visualization of the facial nerve from the brain stem, through the temporal bone, to the stylomastoid foramen without intravenous contrast. Use of the PETRA sequence, or other ultrashort echo time sequences, should be considered in the MR imaging evaluation of certain skull base tumors and perhaps other facial nerve and temporal bone pathologies.
Highlights
The cisternal, canalicular, labyrinthine, geniculate, tympanic, and mastoid segments of the facial nerve are either not detectable or only faintly visible on noncontrast T1-weighted MR images.[1]
The signal intensity of all facial nerve segments was significantly greater for the 4-minute pointwise encoding time reduction with radial acquisition (PETRA) protocol images compared the IR-FSPGR images (Table 2)
SNR and contrast-to-noise ratio (CNR) values were consistently similar or higher with the 4-minute PETRA protocol compared with the default PETRA protocol (Tables 3 and 4)
Summary
The cisternal, canalicular, labyrinthine, geniculate, tympanic, and mastoid segments of the facial nerve are either not detectable or only faintly visible on noncontrast T1-weighted MR images.[1]. UTE sequences capture signal from rapidly decaying short-T2 tissue, such as cortical bone[3] and middle ear ossicles[4] and, should capture signal from the petrous and mastoid portions of the temporal bone. Peripheral nerves have detectable signal in the ultrashort T2 spectrum,[5] so UTE imaging should provide visualization of the facial nerve. UTE imaging minimizes air-related susceptibility artifacts[6] and would minimize artifacts from the middle ear cavity and mastoid air cells that may contribute to nonvisualization of the facial nerve on spin-echo and gradient-echo sequences. The pointwise encoding time reduction with radial acquisition (PETRA) UTE sequence provides more con
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