Purpose
To develop 3D ultrashort‐TE (UTE) sequences with tight TE intervals (δTE), allowing for accurate mapping of lungs under free breathing.
Methods
We have implemented a four‐echo UTE sequence with δTE (< 0.5 ms). A Monte‐Carlo simulation was performed to identify an optimal number of echoes that would result in a significant improvement in the accuracy of the fit within an acceptable scan time. A validation study was conducted on a phantom with known short values (< 5 ms). The scanning protocol included a combination of a standard multi‐echo UTE with six echoes (2.2‐ms intervals) and a new four‐echo UTE (TE < 2 ms) with tight TE intervals δTE. The human imaging was performed at 3 T on 6 adult volunteers. mapping was performed with mono‐exponential and bi‐exponential models.
Results
The simulation for the proposed 10‐echo acquisition predicted over 2‐fold improvement in the accuracy of estimating the short compared with the regular six‐echo acquisition. In the phantom study, the was measured up to three times more accurately compared with standard six‐echo UTE. In human lungs, maps were successfully obtained from 10 echoes, yielding average values = 1.62 ± 0.48 ms for mono‐exponential and = 1.00 ± 0.53 ms for bi‐exponential models.
Conclusion
A UTE sequence using δTE was implemented and validated on short phantoms. The sequence was successfully applied for lung imaging; the bi‐exponential signal model fit for human lung imaging may provide valuable insights into the diseased human lungs.