Relaxivity of Gd-EOB-DTPA in the normal and biliary obstructed guinea pig.

After injection of Gd-EOB-DTPA, T1 and T2 were determined on a clinical MR scanner (1.5 T) in the liver and kidneys of sacrificed but intact guinea pigs with normal and obstructed biliary systems and in bile, urine, and blood collected postmortem. Tissue [Gd] was determined by radioassay of 153Gd and relaxivities (R1 and R2; units of s(-1) x mmol(-1) x kg) of Gd-EOB-DTPA calculated. Compared with R1 in 2% agarose gel (4.49 +/- 0.03), in normal animals R1 was increased in liver (9.3 +/- 0.5), similar in kidney cortex (4.1 +/- 0.5), but reduced in kidney medulla (2.5 +/- 0.4) and papilla (2.7 +/- 0.4). Chronic biliary obstruction did not change R1 in liver (9.7 +/- 4.3) but reduced R1 further in kidney tissues (1.0-0.4). In normal animals, R2 values of all tissues (9.5-18.4) were greater than R2 in gel (5.72 +/- 0.12). Biliary obstruction possibly elevated R2 in liver (40.1 +/- 63.5), severely depressed R2 in kidney cortex (-4.2 +/- 6.2) and medulla (-2.3 +/- 5.4), and reduced R2 in papilla (5.4 +/- 4.6). Obstruction had little effect on R1 and R2 in bile and urine. Water content, macromolecular binding, microviscosity, compartmentalization, and susceptibility effects can readily account for the R1 and R2 observed in liver and kidney. Negative R2 could be a result of several factors, including reduced endogenous magnetic field gradients due to "susceptibility matching" as [Gd] increased, changes in tissue T2 with period of ligation, or a physiological effect of EOB-DTPA. These results show that disease can alter both R1 and R2 from their values in normal tissues.