Fig. 3: The in vivo r1-r2* relaxivity provides a unique contrast in the brain.
From: Non-invasive assessment of normal and impaired iron homeostasis in the brain
a The dependency of R1 on R2* in four representative brain regions; occipital white matter (WM-occipital), occipital cortex (CTX-occipital), Thalamus & Putamen of a single subject. R2* and R1 measurements across voxels were binned (dots represent the median; shaded areas represent the mean absolute deviation), and a linear fit was calculated. The slopes of the linear fit represent the dependency of R1 on R2* (r1-r2* relaxivity) and vary across brain regions. b The r1-r2* relaxivity across the brain. Left: the r1-r2* relaxivity in different brain regions, the variation in each region is across normal subjects (age 27 ± 2, N  =  21). Within-region, this measurement is stable across subjects. It shows clear difference between regions, thus indicating its reliability. The 25th, 50th, and 75th percentiles and extreme data points are shown for each box. Right: the contrast of the r1-r2* relaxivity across the brain. Red, yellow and gray distributions represent the values of the r1-r2* relaxivities in sub-cortical (sub-CTX), white-matter (WM) and cortical (CTX) brain regions, respectively. c, d Similar analyses for R1 and R2* values, in which the gray-matter vs. white-matter contrast is much more dominant compared to the r1-r2* relaxivity. Hence, the r1-r2* relaxivity provides distinct information compared to R1 and R2*, beyond the WM-GM separation. Results in this entire figure are for ROIs in the left hemisphere.
