title: MRI image plane nonuniformity in evaluation of ferrous sulphate dosimeter gel (FeGel) by means of T1-relaxation time.
abstract: MR image nonuniformity can vary significantly with the spin-echo pulse sequence repetition time. When MR images with different nonuniformity shapes are used in a T1-calculation the resulting T1-image becomes nonuniform. As shown in this work the uniformity TR-dependence of the spin-echo pulse sequence is a critical property for T1 measurements in general and for ferrous sulfate dosimeter gel (FeGel) applications in particular. The purpose was to study the characteristics of the MR image plane nonuniformity in FeGel evaluation. This included studies of the possibility of decreasing nonuniformities by selecting uniformity optimized repetition times, studies of the transmitted and received RF-fields and studies of the effectiveness of the correction methods background subtraction and quotient correction. A pronounced MR image nonuniformity variation with repetition and T1 relaxation time was observed, and was found to originate from nonuniform RF-transmission in combination with the inherent differences in T1 relaxation for different repetition times. The T1 calculation itself, the uniformity optimized repetition times, nor none of the correction methods studied could sufficiently correct the nonuniformities observed in the T1 images. The nonuniformities were found to vary considerably less with inversion time for the inversion-recovery pulse sequence, than with repetition time for the spin-echo pulse sequence, resulting in considerably lower T1 image nonuniformity levels.
authors.affiliation: Lund University, Department of Radiation Physics, Malmö University Hospital, Sweden. Peter.Magnusson@rfa.mas.lu.se
authors.forename: P
authors.initials: P
authors.lastname: Magnusson
authors.forename: S A
authors.initials: SA
authors.lastname: Bäck
authors.forename: L E
authors.initials: LE
authors.lastname: Olsson
mesh_terms: D001417:Background Radiation; D005296:Ferrous Compounds; D005782:Gels / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry; D012015:Reference Standards; D013382:Subtraction Technique; D013997:Time Factors
chemical_list: D005296:Ferrous Compounds; D005782:Gels; C020748:ferrous sulfate