Figure shows that the amplitude of the proton signal was larger in plasma samples than in whole-blood samples. This is an effect of higher water content and slower proton relaxation in plasma compared to the whole blood, where the cellular component is dominated by hemoglobin-rich red blood cells . At 10 µT, proton relaxation times were determined as: T blood 1 = 0.305(9) s, T blood 2 = 0.295(2) s; T plasma 1 = 0.39(3) s, T plasma 2 = 0.304(1) s. As shown, the difference in T 1 between whole blood and plasma is higher than in T 2 , which reveals the stronger influence of the cell components on the T 1 relaxation and agrees with low-field NMR relaxometry . Especially in venous whole-blood samples, intracellular heterogeneous distribution of the paramagnetic molecules, such as deoxygenated hemoglobin, might cause magnetic-susceptibility difference between the blood cell and plasma, which contributes to the T 2 relaxation by dephasing water-proton coherence . However, this mechanism becomes insignificant in ULF regime, which allows one to measure heterogeneous samples without susceptibility broadening .