Comparison of two quantitative proton density mapping methods in multiple sclerosis

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 (PD ref , bias-field method) and PD alt (alternative method). Results PD alt -values closely matched PD ref , both for patients and controls. In contrast, ρ (T1) differed by up to 3 % from PD ref, and the voxel-wise correlation between PD ref and ρ (T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ (T1) and PD ref 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 PD alt and PD ref . 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.