Real‐time water/fat imaging at 0.55T with spiral out‐in‐out‐in sampling

Abstract

AbstractPurposeTo develop an efficient and flexible water/fat separated real‐time MRI (RT‐MRI) method using spiral out‐in‐out‐in (OIOI) sampling and balanced SSFP (bSSFP) at 0.55T.MethodsA bSSFP sequence with golden‐angle spiral OIOI readout was developed, capturing three echoes to allow water/fat separation. A low‐latency reconstruction that combines all echoes was available for online visualization. An offline reconstruction provided water and fat RT‐MRI in two steps: (1) image reconstruction with spatiotemporally constrained reconstruction (STCR) and (2) water/fat separation with hierarchical iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (HIDEAL). In healthy volunteers, spiral OIOI was acquired in the wrist during a radial‐to‐ulnar deviation maneuver, in the heart without breath‐hold and cardiac gating, and in the lower abdomen during free‐breathing for visualizing small bowel motility.ResultsWe demonstrate successful water/fat separated RT‐MRI for all tested applications. In the wrist, resulting images provided clear depiction of ligament gaps and their interactions during the radial‐to‐ulnar deviation maneuver. In the heart, water/fat RT‐MRI depicted epicardial fat, provided improved delineation of epicardial coronary arteries, and provided high blood‐myocardial contrast for ventricular function assessment. In the abdomen, water‐only RT‐MRI captured small bowel mobility clearly with improved water‐fat contrast.ConclusionsWe have demonstrated a novel and flexible bSSFP spiral OIOI sequence at 0.55T that can provide water/fat separated RT‐MRI with a variety of application‐specific temporal resolution and spatial resolution requirements.