FIGURE 9.

High gradient head imaging. The displayed parameters are amplitude coefficient A, total scan time T_scan (min:s) and relative scan time for the same SNR, τ_scan. Top row: three perpendicular slices of the same 3D volume acquired with PETRA. Bottom row: the corresponding HYFI images are of comparable quality but τ_scan is considerably reduced. Thanks to the short dead time (Δt = 15 μs) and the high bandwidth (2 MHz), these proton density‐weighted images contain and resolve signals from short‐T ₂ materials and tissues, such as the plastic cover of the ear protection helmet, teeth, skull and other bones, and possibly myelin in the brain. Furthermore, high robustness against local susceptibility gradients is observed in the sinuses. The higher scan efficiency of HYFI as well as reduced acoustic noise considerably improve patient comfort during such a long scan. Note that the artifact in the neck region (first column) is created by signal stemming from the chest area, which is aliased into the field of view due to gradient ambiguity