Magnetic Resonance Imaging (MRI) for Non-invasive Analysis of Hepatic Function After Hemorrhagic Shock in the Rat

Abstract

Background:

The aim of this study was to investigate hepatic macrophage activation and hepatocellular function after hemorrhagic shock in the rat using contrast-enhanced magnetic resonance imaging (MRI). In comparison to techniques requiring open surgery, such as intravital microscopy, MRI is a non-invasive tool; the experimental subject therefore remains intact, enabling the investigator to conduct additional follow-up procedures that may have important clinical implications.

Materials and Methods:

At 3 and 24 h following standardized hemorrhagic shock (40 mmHg for 90 min), MRI (2.4 T Magnet, Biospec, Bruker Karlsruhe, Germany) was performed. After application of a liver-specific contrast dye (Gd-EOB-DTPA; 50 μmol/kg BW), which is absorbed from hepatocytes and secreted into the gall fluid, the signal intensity (SI) was measured. For determination of hepatic macrophage activation, superparamagnetic ferrumoxid particles (ENDOREM^® 10 μmol/kg BW) were injected and the SI was measured again. These data were compared with the findings of in vivo microscopy and bile flow performed in the animals after MRI. The sham groups received 2 ml/h Ringers Lactate for 24 h without initial hemorrhagic shock and reperfusion.

Results:

In the shock group, a significantly smaller increase of SI enhancement after application of Gd-EOB-DTPA (shock group: 126.1%±10.4; sham group 159.3±3.5; p < 0.05) was found compared to the sham group 24 h after shock, which correlated with the bile flow measured. Application of ENDOREM^® resulted in a decrease of SI in T2-weighted images after 3 h compared to 24 h after shock; however, no differences between the shock and sham animals could be observed (shock group -69.8%±2.8; sham group -75.8±1.6; p < 0.05). Intravital microscopy revealed a significant increase of latex beads in hepatic macrophages 3 h after shock compared to sham animals, thereby indicating enhanced macrophage activation. Intravital microscopy showed a significant increase of temporary and permanent adherent leukocytes 3 and 24 h after shock.

Conclusion:

Contrast-enhanced MRI is a useful, noninvasive method for long-term investigations of the liver after hemorrhagic shock, specifically with respect to monitoring alterations of hepatocellular function. However, a significant hepatic macrophage activation after shock was only observed by direct measurement of latex beads using intravital microscopy and not with contrast-enhanced MRI.