ΔR2*/ΔR2 ratios for all subjects for the early and later part of the GE HRF (2–3 mm and 1–2 mm sections).

Normalizing the SE and GE HRFs across cortical depth and by the used echo times, yielding ΔR2*(t) and ΔR2(t) respectively, makes it possible to compare two contrasts in more detail [32]. The ratio of ΔR2* to ΔR2 is an indication of the measured vessel sizes [33]. Larger ratio means larger vessels are probed. The ratio was computed for the GE HRF at 2–3, i.e. the K value in Figure 3A, and 1–2 mm cortical depth sections using the SE HRF.* denotes a significant difference with column to the right, one-sided paired Student's t-test for P