Quantitative theory for the longitudinal relaxation time of blood water

Abstract

Purpose: To propose and evaluate a model for the blood water T1 that takes into account the effects of hematocrit fraction, oxygenation fraction, erythrocyte hemoglobin concentration, methemoglobin fraction, and plasma albumin concentration.

Methods: Whole blood and lysed blood T1 data were acquired at magnetic fields of 3 Tesla (T), 7T, 9.4T, and 11.7T using inversion-recovery measurements and a home-built blood circulation system for maintaining physiological conditions. A quantitative model was derived based on multivariable fitting of this data.

Results: Fitting of the model to the data allowed determination of the different parameters describing the blood water T1 such as those for the diamagnetic and paramagnetic effects of albumin and hemoglobin, and the contribution of methemoglobin. The model correctly predicts blood T1 at multiple fields, as verified by comparison with existing literature.

Conclusion: The model provides physical and physiological parameters describing the effects of hematocrit fraction, oxygenation, hemoglobin concentration, methemoglobin fraction, and albumin concentration on blood water T1 . It can be used to predict blood T1 at multiple fields. Magn Reson Med 76:270-281, 2016. © 2015 Wiley Periodicals, Inc.

Keywords: Hct; T1 model; albumin; hematocrit fraction; hemoglobin concentration; in vitro blood; longitudinal relaxation; methemoglobin fraction; oxygenation; relaxivity.

Figure 1

a) The dependence of lysed blood R₁ values on the methemoglobin’s concentration. b) Linear fitting of lysed blood R₁ values as a function of methemoglobin’s concentration under fully oxygenated conditions.

Figure 2

a) The dependence of lysed blood R₁ values on the hemoglobin’s concentration. b) Linear fitting of the corrected lysed blood relaxation rate ΔR₁ as a function of hemoglobin’s molality concentration at fully oxygenated conditions.

Figure 3

Histogram summarizing the relative errors between the experimental whole blood R₁ and fitted R₁.

Figure 4

The magnetic field dependence of r_1dia,Hb (a), r_1dia,Alb (b), r_{1para,deoxyHb} (c) r_1para,MetHb (d) and R_1saline (e), and numerical fitting using Freed’s equation (65,66) (paramagnetic relaxivity, solid line) and Lindstrom and Koenig’s Equation (16) (diamagnetic relaxivity and R_1saline, solid line)