Fig. 6.

(Ai) R₁ histograms in grey matter (top) and white matter (bottom) for one subject's data acquired with different levels of fat suppression (FS) by varying the flip angle of the SPIR pulse. The black line represents data acquired with no FS and the colour solid lines represent data acquired with FS SPIR flip angles ranging from 30° (red) to 70° (violet). The dashed colour lines show corresponding R₁ histograms after correction using: b/a data generated by linear regression of R₁ versus SPIR flip angle to correct (Eqn. (2)) using: (i) voxelwise correction (the b/a parameter map was spatially smoothed by a Gaussian kernel with a full width at half maximum (FWHM) of 2 mm prior to correction) and a global b/a correction with the constant b/a parameter value computed from (ii) the full dataset comprising 5 FS flip angles of 30°, 40°, 50°, 60° and 70° and (iii) a reduced dataset of two FS flip angles of 40° and 70° only. (B) (i) Original R₁ maps (first row) shown for the different SPIR flip angles (including data acquired with no fat suppression, right) and corresponding R₁ maps after correction with the different methods. (ii) Difference image between T₁ maps for data acquired with SPIR FA=70° (uncorrected and corrected with the different methods) and data acquired with no FS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)