Multi-echo IDEAL Cardiac Water-Fat Imaging

Introduction In cardiac magnetic resonance imaging, separation of water and fat signals is important for improved visualization of enhancing myocardium and pericardial disease, as well as direct visualization of fat in pathologies such as arrythmogenic right ventricular cardiomyopathy (ARVC), fatty tumors, and fatty infiltration of chronic myocardial infarctions. Fat can appear similar to slow blood flow with some methods, and fat may obscure enhancing myocardium, particularly epicardial enhancement that can occur in myocarditis, pericarditis, and non-ischemic cardiomyopathies. Chemical shift based water-fat separation methods have been used to provide separate water and fat images in balanced-SSFP CINE imaging [1] and myocardial viability imaging [2,3]. Here, we demonstrate the ability of IDEAL [1,4] to decompose fat and water signals in cardiac imaging with a gated multi-echo segmented gradient-echo sequence. Included are the use of near-optimal TE increments that maximize SNR performance [4] and a modified version of an advanced field-map estimation method with region-growing [5]. Methods A multi-echo gradient echo sequence with 3 echoes acquired with positive (fly-back) readouts was implemented with and without inversion recovery (IR) at 1.5T (Signa HDx, GE Healthcare, Milwaukee, WI). Parameters included: TR/TE1/ΔTE/BW = 7.2-7.8/1.51.7/1.9-2.0/±100kHz; FOV/Matrix/Slice Thickness = 35cm/192x192/6-8mm; 16-32 views per segment; and one segment in each or every second cardiac cycle, for a duration of 13-25 cardiac cycles per slice. In addition, a T2-preparation sequence (T2-Prep) with or without IR was available [6,7]. The technique was demonstrated in patients and volunteers for several clinical imaging situations. Results An example of “rule-out” suspected ARVC is shown in Figure 1, acquired in diastole without IR. A conventional double-IR blackblood sequence (1a) used for comparison showed high signal in the mid RV wall concerning for fat vs. slow flow (arrows). This was easily resolved as blood and not fat using IDEAL (1b,1c) images. Myocardial viability imaging with IR (TI=200ms) for suppression of myocardial signal is shown in Figure 2 (no infarct in this patient), with good separation of water (2a) and fat (2b) signal.