Optimizing 3D EPI for rapid T₁‐weighted imaging

Abstract

Funding information GE HealthcarePurpose: To investigate the use of 3D EPI for rapid T 1 -weighted brain imaging, focusing on the RF pulse's influence on the contrast between gray and white matter. Methods: An interleaved 3D EPI sequence use partial Fourier and CAIPIRINHA sampling was used to acquire T 1 -weighted brain volumes with isotropic resolution, low echo times, and low geometric distortions. Five different RF pulses were evaluated in terms of fat suppression performance and gray-white matter contrast. Two binomial RF pulses were compared to a single rectangular (WE-rect) RF pulse exciting only water, and two new RF pulses developed in this work, where one was an extension of the WE-rect, and the other was an SLR pulse. The technique was demonstrated in three clinical cases, where brain tumor patients were imaged before and after gadolinium administration. Results: A fat-suppressed 3D EPI sequence with a phase encoding bandwidth of around 100 Hz was found to exhibit a good trade-off between geometrical distortions and scan duration. Whole-brain T 1 -weighted 3D EPI images with 1.2 mm isotropic voxel size could be acquired in 24 seconds. The WE-rect, its extension, and the SLR RF pulses resulted in reduced magnetization transfer effects and provided a 20% mean increase in gray-white matter contrast. Conclusion: Using a high phase encoding bandwidth and RF pulses that reduce magnetization transfer effects, a fat-suppressed multi-shot 3D EPI sequence can be used to rapidly acquire isotropic T 1 -weighted volumes.

Segmented K-Space Blipped-Controlled Aliasing in Parallel Imaging (Skipped-CAIPI) for High Spatiotemporal Resolution Echo Planar Imaging

“…Segmentation can be applied along the shot-selective CAIPI trajectory to achieve even larger y -blips as a multiple of the shot-selective y -blip (6). In this work, we go one step further and propose segmentation along the blipped-CAIPI trajectory to also obtain all intermediate y -blips and EFs .…”

“…2 used sagittal slice orientation (readout: head-feet). All EPI scans employed a single hard pulse excitation set to approximately 2.4ms duration for water excitation at 3T (6,43). A single external PC scan (5° excitation) followed by 100 FLASH dummy shots and ACS lines (44) were acquired as a prescan (Fig.…”

“…Furthermore, the 2 × 2 z 1 pattern was sampled with varying segmentation factors, S = 15,10,5. Finally, 1.2mm isotropic data were acquired, adapting and extending a rapid T 1 -weighted scan recently proposed for clinical use (6): for consistent TR=15.7ms and TE=4.35ms across different CAIPI patterns, EF = 7 and minimal sequence dead times and shots per measurement were maintained by adjusting S as facilitated by skipped-CAIPI (Tab. 2).…”

“…An increasing number of structural imaging (1–6), quantitative imaging (7–10) or high spatiotemporal resolution functional imaging (11–21) applications have been approached by dedicated echo planar imaging (EPI) (22) implementations. Many of those aim at higher spatial resolution than usual, e.g.…”

“…base resolution and echo time) often enforce a suboptimal CAIPI pattern instead of a noise-optimal one. Recently, shot-selective CAIPI has been combined with interleaved multi-shot segmentation fostering rapid T 1 -weighted anatomical imaging (6). Still, this approach is limited to only a fraction of traditional segmentation options without controlled aliasing.…”