18, 19 With ongoing MR imaging technical advances enabling ever-faster scan times and higher contrast/spatial resolution, there is a potential for this single technique to provide comprehensive imaging assessment for patients, a “one-stop shop.” In this report, we discuss our initial experience with ZTE and provide multiple examples demonstrating the diagnostic utility of the sequence for craniofacial bone imaging. In ZTE, readout gradients are turned on before the RF pulse so that data acquisition can begin immediately after excitation. This requires high-performance coils with rapid transmit/receive switching capabilities and uses center-out k-space encoding. With ZTE, the readout gradient is already on during the RF pulse, precluding conventional section/slab selection. This necessitates a high-bandwidth excitation with a short-duration hard pulse to ensure that the excitation is as homogeneous and as consistent as possible across the entire FOV from repetition to repetition. The RF excitation is immediately followed by a 3D data acquisition. Gradients are used continuously and modulated between repetitions to sample data along radial trajectories in k-space, rather than being rapidly turned on and off. This process minimizes mechanical vibration and enables a virtually silent technique. Fully sampling the k-space with radial trajectories requires significantly more repetitions (TRs) than an equivalent 3D Cartesian acquisition. Reduction of total scan time is achieved with the use of short TRs and small flip angles for quasi-steady-state magnetization. ![]() Most scan time is targeted toward data acquisition, with minimal dead time occurring during the RF pulse and a single gradient step (On-line Fig 1). The technique uses lower changes in amplitude over time (dB/dt) than con-ventional sequences low flip angles and built-in scanner safety measures counter the short RF pulse duration that would otherwise raise concern for a high specific absorption rate (SAR).ģ- 6 This feature permits rapid isotropic scanning with high resistance to artifacts, including susceptibility and motion.
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