Lung T₂* mapping using 3D ultrashort TE with tight intervals TE

Purpose: To develop 3D ultrashort-TE (UTE) sequences with tight TE intervals (delta TE), allowing for accurate T-2* mapping of lungs under free breathing. Methods: We have implemented a four-echo UTE sequence with delta TE (< 0.5ms). A Monte-Carlo simulation was performed to identify an optimal number of echoes thatwould result in a significant improvement in the accuracy of the T-2* fitwithin an acceptable scan time. Avalidation studywas conducted on a phantomwith known short T-2* values (< 5ms). 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< 2ms) with tight TE intervals delta TE. The human imaging was performed at 3 T on 6 adult volunteers. T-2* 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 T-2* compared with the regular six-echo acquisition. In the phantom study, the T-2* was measured up to three times more accurately compared with standard six- echo UTE. In human lungs, T-2* mapswere successfully obtained from 10 echoes, yielding average values T-2* = 1.62 +/- 0.48 ms for mono-exponential and T-2s* = 1.00 +/- 0.53 ms for bi-exponential models. Conclusion: A UTE sequence using dTE was implemented and validated on short T-2* 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.