SPARCQ: A new approach for fat fraction mapping using asymmetries in the phase‐cycled balanced SSFP signal profile

Abstract

AbstractPurposeTo develop SPARCQ (Signal Profile Asymmetries for Rapid Compartment Quantification), a novel approach to quantify fat fraction (FF) using asymmetries in the phase‐cycled balanced SSFP (bSSFP) profile.MethodsSPARCQ uses phase‐cycling to obtain bSSFP frequency profiles, which display asymmetries in the presence of fat and water at certain TRs. For each voxel, the measured signal profile is decomposed into a weighted sum of simulated profiles via multi‐compartment dictionary matching. Each dictionary entry represents a single‐compartment bSSFP profile with a specific off‐resonance frequency and relaxation time ratio. Using the results of dictionary matching, the fractions of the different off‐resonance components are extracted for each voxel, generating quantitative maps of water and FF and banding‐artifact‐free images for the entire image volume. SPARCQ was validated using simulations, experiments in a water‐fat phantom and in knees of healthy volunteers. Experimental results were compared with reference proton density FFs obtained with 1H‐MRS (phantoms) and with multiecho gradient‐echo MRI (phantoms and volunteers). SPARCQ repeatability was evaluated in six scan‐rescan experiments.ResultsSimulations showed that FF quantification is accurate and robust for SNRs greater than 20. Phantom experiments demonstrated good agreement between SPARCQ and gold standard FFs. In volunteers, banding‐artifact‐free quantitative maps and water‐fat‐separated images obtained with SPARCQ and ME‐GRE demonstrated the expected contrast between fatty and non‐fatty tissues. The coefficient of repeatability of SPARCQ FF was 0.0512.ConclusionSPARCQ demonstrates potential for fat quantification using asymmetries in bSSFP profiles and may be a promising alternative to conventional FF quantification techniques.