René-Maxime Gracien1,2, Sarah C Reitz3,4, Marlies Wagner5,4, Christoph Mayer3, Steffen Volz4, Stephanie-Michelle Hof3,4, Vinzenz Fleischer6,7, Amgad Droby6,7, Helmuth Steinmetz3, Sergiu Groppa6,7, Elke Hattingen5,4, Johannes C Klein3,4,8, Ralf Deichmann4. 1. Department of Neurology, Goethe University, Frankfurt/Main, Germany. Rene-Maxime.Gracien@kgu.de. 2. Brain Imaging Center, Goethe University, Frankfurt/Main, Germany. Rene-Maxime.Gracien@kgu.de. 3. Department of Neurology, Goethe University, Frankfurt/Main, Germany. 4. Brain Imaging Center, Goethe University, Frankfurt/Main, Germany. 5. Department of Neuroradiology, Goethe University, Frankfurt/Main, Germany. 6. Department of Neurology, Johannes Gutenberg University, Mainz, Germany. 7. Neuroimaging Center (NIC) of the Focus Program Translational Neuroscience (FTN), Johannes Gutenberg University, Mainz, Germany. 8. Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
Abstract
OBJECTIVE: Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MS patients. MATERIALS/ METHODS: PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PDref, bias-field method) and PDalt (alternative method). RESULTS: PDalt-values closely matched PDref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PDref, and the voxel-wise correlation between PDref and ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PDref were almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PDalt and PDref. CONCLUSION: RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MS patients, in spite of discrepancies between ρ(T1) and actual PD values.
OBJECTIVE: Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MSpatients. MATERIALS/ METHODS:PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PDref, bias-field method) and PDalt (alternative method). RESULTS: PDalt-values closely matched PDref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PDref, and the voxel-wise correlation between PDref and ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PDref were almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PDalt and PDref. CONCLUSION: RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MSpatients, in spite of discrepancies between ρ(T1) and actual PD values.
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