Dysprosium‐bearing red cells as potential transverse relaxation agents for MRI

The cytosol of intact human red blood cells was loaded with 28.1 ± 3.4 mM of dysprosium DTPA‐BMA using a hypoosmotic technique. When loaded cells were diluted with saline and control cells to give an average dysprosium concentration of 3.3 ± 0.5 mM, the transverse relaxation rate constants R   * 2and R 2 increased. R   * 2increased from 7.5 ± 0.9 sec −1 to 356 ± 50 sec −1 , and R 2 increased from 7.4 ± 0.7 sec –1 to 148 ± 40 sec −1 . After lysing, R   * 2was 6.0 ± 0.6 sec −1 in the control and 13.4 ± 1.5 sec −1 in the mixture; R 2 was 6.4 ± 1.1 sec −1 and 9.8 ± 2.4 sec −1 , respectively. Thus, the relaxivity effects were enhanced by sequestration of the dysprosium within intact red cells, and this effect was lost after lysis. At a circulating whole‐blood concentration of 0.81 ± 0.15 mM in rats, the liver signal intensity dropped 29.9% ± 3.7% and kidney signal intensity dropped 19.4% ± 8.7%. Dysprosium‐loaded cells might be useful in the study of perfusion and tissue blood volume. Magn Reson Med 45:920–923, 2001. © 2001 Wiley‐Liss, Inc.