Effect of hemolysis and clotting on proton relaxation times of blood.

The proton relaxation times T1 and T2 of plasma and clotted blood stored in test tubes were studied at a magnetic field of 0.225 T as a function of time. A satisfactory description of both relaxation processes could be made by two exponential components for the plasma and three components for the clot. The major relaxation component in plasma was the slower one, the T1 of which shortened from about 1 300 ms to about 400 ms between the second and sixth day of storage. The plasma T2 behaved similarly, but shortened less. The shortening of the relaxation time in plasma surrounding the experimental thrombus was concluded to be due to a number of factors, including the release of hemoglobin into plasma, the conversion of hemoglobin to methemoglobin, a concomitant change in the configuration of hemoglobin molecules, and an increased concentration of iron in plasma. The shortening of the relaxation time may also occur in an in vivo hematoma and change the magnetic resonance appearance of a hematoma with time.