WE-G-217A-01: Fast Recovery Driven Equilibrium with Automated Switching to Avoid Artifacts.

PURPOSE To reduce image artifacts from the unnecessary use of driven- equilibrium. Driven-equilibrium methods known as fast recovery, RESTORE, or DRIVE enable reduction of repetition time (TR) and hence acquisition time in RARE (FSE or TSE) imaging by applying additional RF pulses following each echotrain to accelerate T1 recovery. Fast recovery (FR) techniques are most useful when TR is less than 4*T1. For neuroimaging, the benefit of FR diminishes as TR increases beyond ∼3s. In regions of rapid susceptibility change such as near metallic implants, FR techniques can introduce artifact because the magnetization is not properly rephased when the FR pulses are applied. In our clinical practice we observe that technologists frequently adjust TR over a range of 2-5s on a patient- specific basis to minimize scan time. We do not observe, however, that technologists reliably disable FR when TR is long enough, introducing possible artifacts. METHODS An FR-FSE pulse sequence was modified to automatically disable the FR feature whenever TR exceeded a user-defined threshold (TR0). Under IRB approval, a healthy volunteer was scanned with the sequence using TRs ranging from 1-5s, and TR0=900ms or 6s. Contrast- to-noise measurements were made between CSF, gray matter and white matter for each dataset. RESULTS The volunteer study shows decreasing benefit of FR as TRs increase beyond 3s. A patient with bilateral auditory brainstem implants scanned with and without FR demonstrates FR-induced artifacts. CONCLUSIONS We demonstrate an FR-FSE pulse sequence that automatically disables fast-recovery whenever TR exceeds an operator- selected threshold. The pulse sequence avoids unnecessary artifacts in regions of rapid susceptibility changes, while retaining the advantages of FR when TR<TR0. Clinical images from a patient with bilateral auditory brainstem implants demonstrate potential artifacts introduced by FR, and the benefits of automatically avoiding unnecessary use of FR.