Application of spin echoes in the regime of weak dephasing to T -mapping of the lung.

Purpose: This work presents an approach to mapping the entire lung's proton density and T within a single breath-hold and analyzes the apparent T when exciting with a spin echo generating pulse in comparison to a standard gradient echo acquisition.

Methods: An inversion-recovery SNAPSHOT-FLASH sequence with a stack-of-stars k-space readout with a golden angle increment was modified to use a spin echo generating radiofrequency-pulse for excitation. Data of five volunteers were acquired on a 3T scanner and image reconstruction was performed by an iterative algorithm adopted from MR-Fingerprinting.

Results: The feasibility of acquiring quantitative maps of the entire lung with a resolution of 5 × 5 × 10 mm within 7.5 s is demonstrated. It is shown that the proposed spin echo forming radiofrequency-pulse increases the apparent proton density compared to a rectangular pulse. Further, the apparent T is reduced in the spin echo case compared to the gradient echo sequence.

Conclusion: The proposed spin echo based method results in T maps that are comparable to the ones that were acquired with ultra-short echo time sequences elsewhere. The T shortening is believed to originate from increased signal contributions of the extra vascular compartment, which has a short T2∗ and T . Magn Reson Med 79:960-967, 2018. © 2017 International Society for Magnetic Resonance in Medicine.