Fat fraction mapping using bSSFP Signal Profile Asymmetries for Robust multi-Compartment Quantification (SPARCQ)

Purpose: To develop a novel quantitative method for detection of different tissue compartments based on bSSFP signal profile asymmetries (SPARCQ) and to provide a validation and proof-of-concept for voxel-wise water-fat separation and fat fraction mapping. Methods: The SPARCQ framework uses phase-cycled bSSFP acquisitions to obtain bSSFP signal profiles. For each voxel, the profile is decomposed into a weighted sum of simulated profiles with specific off-resonance and relaxation time ratios. From the obtained set of weights, voxel-wise estimations of the fractions of the different components and their equilibrium magnetization are extracted. For the entire image volume, component-specific quantitative maps as well as banding-artifact-free images are generated. A SPARCQ proof-of-concept was provided for water-fat separation and fat fraction mapping. Noise robustness was assessed using simulations. A dedicated water-fat phantom was used to validate fat fractions estimated with SPARCQ against gold-standard 1H MRS. Quantitative maps were obtained in knees of six healthy volunteers, and SPARCQ repeatability was evaluated in scan rescan experiments. Results: Simulations showed that fat fraction estimations are accurate and robust for signal-to-noise ratios above 20. Phantom experiments showed good agreement between SPARCQ and gold-standard (GS) fat fractions (fF(SPARCQ) = 1.02*fF(GS) + 0.00235). In volunteers, quantitative maps and banding-artifact-free water-fat-separated images obtained with SPARCQ demonstrated the expected contrast between fatty and non-fatty tissues. The coefficient of repeatability of SPARCQ fat fraction was 0.0512. Conclusion: The SPARCQ framework was proposed as a novel quantitative mapping technique for detecting different tissue compartments, and its potential was demonstrated for quantitative water-fat separation.Comment: 20 pages, 7 figures, submitted to Magnetic Resonance in Medicin

Getting the phase consistent: The importance of phase description in balanced steady-state free precession MRI of multicompartment systems

Purpose: Determine the correct mathematical phase description for balanced steady-state free precession (bSSFP) signals in multicompartment systems. Theory and Methods: Based on published bSSFP signal models, two distinct phase descriptions can be formulated: one predicting the presence and the other predicting the absence of destructive interference effects in multicompartment systems. Numerical simulations of bSSFP signals of water and acetone were performed to evaluate the predictions of these two distinct phase descriptions. For experimental validation, bSSFP profiles were measured at 3T using phase-cycled bSSFP acquisitions performed in a phantom containing mixtures of water and acetone, which replicates a system with two signal components. Localized single voxel MRS was performed at 7T to determine the relative chemical-shift of the acetone-water mixtures. Results: Based on the choice of phase description, the simulated bSSFP profiles of water-acetone mixtures varied significantly, either displaying or lacking destructive interference effects, as predicted theoretically. In phantom experiments, destructive interference was consistently observed in the measured bSSFP profiles of water-acetone mixtures, an observation which excludes the phase description that predicts an absence of destructive interference. The connection between the choice of phase description and predicted observation enables an unambiguous experimental identification of the correct phase description for multicompartment bSSFP profiles, which is consistent with Bloch equations. Conclusion: The study emphasizes that consistent phase descriptions are crucial for accurately describing multi-compartment bSSFP signals, as incorrect phase descriptions result in erroneous predictions.Comment: Submitted to Magn. Reson. Me

SPARCQ: A new approach for fat fraction mapping using asymmetries in the phase-cycle bSSFP signal profile

This repository contains in vitro and in vivo MRI data acquired on a 3T clinical system (MAGNETOM Prismafit, Siemens Healthcare, Erlangen, Germany) using a commercially available 18-channel body coil. All data includes both magnitude and phase information in DICOM format. Data was collected and used in a study untitled "SPARCQ: A new approach for fat fraction mapping using asymmetries in the phase-cycled bSSFP signal profile" by Rossi et. al. (2023). The detailed contents of the repository are listed below: /PHANTOM: 3D acquisitions of a custom fat-water phantom with 6 vials of different peanut oil and water concentrations /PCbSSFP NPC=37 Phase-Cycled bSSFP acquisitions with phase increments [0°:10°:360°] /MEGRE MultiEcho GRE acquisition with 13 monopolar echoes TE1/$\Delta$TE=1.34/1.98 ms /V1 to /V6: 3D knee acquisitions from n=6 healthy volunteers /Scan NPC=37 Phase-Cycled bSSFP acquisitions with phase increments [0°:10°:360°] /Rescan NPC=37 Phase-Cycled bSSFP acquisitions with phase increments [0°:10°:360°] after volunteer repositioning (repeatability experiment) /Dixon In-phase, out-of-phase, fat-only and water-only images reconstructed from a Turbo Spin Echo Dixon sequence /V7 and /V8: 3D knee acquisitions from n=2 healthy volunteers /Scan NPC=37 Phase-Cycled bSSFP acquisitions with phase increments [0°:10°:360°] /MEGRE MultiEcho GRE acquisition with 13 monopolar echoes TE1/$\Delta$TE=1.34/1.98 ms ************************************************************************************************************************************************************************************************************************************************************ Link to publication: https://onlinelibrary.wiley.com/doi/full/10.1002/mrm.29813 ************************************************************************************************************************************************************************************************************************************************************ Data was collected and approved for sharing according to institutional rules (Ethics Commitee, CHUV, Lausanne, Switzerland)