FAQs
What are the common applications of EPTI?
EPTI can be viewed as a general readout technique and the next-generation EPI, and be readily inserted into the pulse sequence for different MRI contrasts. We and others have demonstrated the applications of EPTI in i) multi-echo fMRI for enhanced fMRI sensitivity; ii) layer fMRI with improved specificity; iii) distortion-free diffusion & diffusion relaxometry; iv) fast quantitative MRI (simultaneous whole brain T1, T2, T2*, PD and B1 mapping in 3 mins at 1-mm iso); v) efficient myelin-water imaging. Other applications can include: perfusion imaing (e.g., ASL, DCE, DSC).
When to use single-shot EPTI and when to use multi-shot EPTI (2D sequence)?
We have originally introduced EPTI as a multi-shot 2D acquisition, which is highly suitable for high-spatial resolution applications, but results in moderate temporal resolution (5-10 s). By developing and optimizing new encoding strategies, we now achieved single-shot EPTI for standard spatial resolution (1.2-3 mm iso) within comparable temporal resolution to single-shot EPI (1-2 s for whole brain coverage), while providing distortion-free densely-sampled multi-echo imaging.
Use multi-shot EPTI if you are targeting at high-spatial resolution or imaging challenging areas without requiring high temporal resolution.
Use single-shot EPTI if you are targeting at standard spatial resolution but requires high temporal resolution and high robustness to motion/physiological noise.
What are the potential artifacts and how to perform correction in EPTI?
One artifact observed in early versions (VE platforms) of the 2D EPTI sequence was signal variation in certain slice groups caused by RF spoiling in the fat-saturation module. This issue has been resolved in the latest VE release (v202506 and later), as well as in the XA and Pulseq versions.
For multi-shot sequences, a common challenge is shot-to-shot phase variation, so in multi-shot EPTI, we offer several correction options in the reconstruction, including global, 1D, and 2D high-order phase correction methods, which effectively correct for these effects. single-shot EPTI is inherently more robust and does not suffer from such shot-to-shot phase inconsistencies.
B0 field fluctuations across volumes (e.g., due to subject motion or respiration) only cause minor signal variations that can be effectively mitigated through a simple B0 update instead of causing dynamic geometric distortions as in EPI, therefore improving temporal stability in EPTI compared to EPI, especially at tissue boundaries such as gray matter (see Fig. 4 and 5 in the single-shot EPTI paper for details). To further improve robustness to motion and physiological noise, post-processing methods that leverage EPTI's rich multi-echo information can further reduce these nuisance effects.
What is the benefit of 3D-EPTI?
3D EPTI improves SNR efficiency for high-resolution imaging—particularly high isotropic resolution—making it well-suited for high-resolution fMRI and quantitative mapping. While 3D EPTI is currently not available, we do have future plans to implement 3D EPTI using Pulseq (to support more sequence platforms). We are also actively working on new 3D EPTI acquisitions for fMRI and other applications. If you're interested, feel free to submit the feedback form or contact us for potential collaborations.