Comparison of t2 relaxation in blood, brain, and ferritin

Abstract

T2 was measured in samples of human blood and monkey brain over a field range of 0.02-1.5 Tesla, with variable interecho times, and was compared with previous data on ferritin solutions (taken with the same apparatus). 1/T2 in deoxygenated blood increased quadratically with field strength, as noted previously, but in brain gray matter the increase was linear, as also was the case in ferritin solution. In both deoxygenated blood and gray matter, 1/T2 increased with interecho time, but appeared to level off at times around 50 msec, as expected from the theory of diffusion through magnetic gradients. Diffusion times estimated by using the chemical exchange approximation were 3.4 msec for deoxygenated blood and 5.7 msec for the globus pallidus. The quadratic field dependence in blood is consistent with this same theory, but the linear dependence in brain tissue and in ferritin solutions remains unexplained.

On the theoretical basis of perfusion measurements by dynamic susceptibility contrast MRI

“…Theoretical reasons (25) suggest a range of possibilities from constant to quadratic dependence. A linear relationship has been found in postmortem blood-free monkey brain specimens (24) and is assumed in the present study, although the limitations of such a transfer are understood. The difference between the GE and SE relaxation rates in blood is neglected.…”

“…This resulted in R 2a0 ϭ 2.76 s Ϫ1 and R 2v0 ϭ 5.97 s Ϫ1 . For blood the validity of such a conversion follows from many reports (23,24), and from the quadratic dependence of the relaxation rate on the blood oxygenation level observed in Ref. 12.…”

“…Then Eq. [5] takes the form c app ͑⌬t͒ ϭ f app ͑0͒c a ͑⌬t͒⌬t [24] c app ͑2⌬t͒ ϭ ͓f app ͑0͒c a ͑2⌬t͒ ϩ f app ͑⌬t͒c a ͑⌬t͔͒⌬t [25] and so on. The initial value f app (0) is defined from Eq.…”

“…The initial value f app (0) is defined from Eq. [24], and then f app (⌬t) is found from Eq. [25], etc.…”

Generalized Moment Analysis of Magnetic Field Correlations for Accumulations of Spherical and Cylindrical Magnetic Perturbers

“…In contrast, the (1, 3)-GMA with the three lowest low and the first high frequency moment approximates the long time limit significantly better than the short time limit. An application to biological tissue is provided in Figure 4C where mono-and bi-exponential approximations in the GMA of the correlation function are visualized for values that are typical for susceptibility gradients based on nonheme ironstorage in brain tissue (through iron-rich oligodendrocytes in the Globus pallidus that approximately have radii R i of 3-4 µm, a frequency shift of δω = 184 s −1 , a tissue density of η = 0.04 and D = 0.76 · 10 −9 m 2 s −1 , leading to τ = 16.12 ms; see [50,51] for more details). It can be seen that the biexponential approximations K (1,3) (t) and K (2,2) (t) are in excellent agreement with the actual correlation function K(t), while the monoexponential functions K i (t) only approximate K(t) sufficiently for t 30 ms.…”