  Purpose: To develop SPARCQ (Signal Profile Asymmetries for Rapid Compartment
Quantification), a novel approach to quantify fat fraction using asymmetries in
the phase-cycled bSSFP profile. Methods: SPARCQ uses phase-cycling to obtain
bSSFP frequency profiles, which display asymmetries in the presence of fat and
water at certain repetition times. 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 fat fraction 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 fat fractions obtained with 1H-MRS
(phantoms) and with multiecho gradient-echo MRI (phantoms and volunteers).
SPARCQ repeatability was evaluated in six scan-rescan experiments. Results:
Simulations showed that fat fraction quantification is accurate and robust for
signal-to-noise ratios greater than 20. Phantom experiments demonstrated good
agreement between SPARCQ and gold standard fat fractions. 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 fat fraction was
0.0512. Conclusion: SPARCQ demonstrates potential for fat quantification using
asymmetries in bSSFP profiles, and may be a promising alternative to
conventional fat fraction quantification techniques.
