Improved Scan Efficiency of 3D Fast Spin Echo with Subspace-Constrained Reconstruction

Introduction: Scan efficiency plays a critical role in Fast Spin Echo (FSE) imaging because of the long TR intervals necessary to achieve the desired image contrast. Given a fixed scan-time budget, there are a finite number of TR intervals to collect echo trains, and this number is independent of the echo train length (ETL). However, in conventional reconstruction, long ETLs cause image blurring and mixed contrast due to uncompensated signal decay [1-3]. Model-based approaches that account for signal decay can overcome this limitation [4-8], but the impact of ETL is unclear when operating in an undersampled regime. In this work, we explore the utility of using a subspace-constrained reconstruction to increase ETLs without increasing noise or image blurring [7]. We show the approach has a fixed SNR cost, independent of ETL, compared to a reconstruction endowed with perfect knowledge of relaxation.