© American Society of Neuroradiology MR Imaging of Various Oxidation

The in vitro behavior of various states of hemoglobin was examined over a wide range of concentrations. Solutions of increasing concentrations of oxyhemoglobin dis-played significant increases in T1 and T2 relaxation rates that were insensitive to pH values between 6.0 and 6.9. Bovine serum albumin, which displayed a relaxation behavior nearly identical to that of oxyhemoglobin, was used to normalize for the protein concentration of the deoxyhemoglobin and methemoglobin samples. Concentrated protein solutions with increasing proportions of deoxyhemoglobin yielded little change in the T1 relaxation rate. In these samples, however, the T2 relaxation rate displayed a parabolic dependence on the concentration of intracellular deoxyhemoglobin paralleling the inhomogeneity of the sample; this was not observed with extracellular deoxyhemo-globin. Similar T2 relaxation behavior was observed for intracellular methemoglobin, except that the magnitude of the T2 shortening was smaller than that for deoxyhemo-globin. The magnitude of the T2 shortening was pH dependent, roughly paralleling the change in the equilibrium between the high-spin acid form of methemoglobin and the low-spin basic form of methemoglobin. Marked increase in the T1 relaxation rate i