Gadobenate dimeglumine as a contrast agent for MRI of the mouse liver

Small animal magnetic resonance imaging: an efficient tool to assess liver volume and intrahepatic vascular anatomy

BACKGROUND

To develop a noninvasive technique to assess liver volumetry and intrahepatic portal vein anatomy in a mouse model of liver regeneration.

MATERIALS AND METHODS

Fifty-two C57BL/6 male mice underwent magnetic resonance imaging (MRI) of the liver using a 4.7 T small animal MRI system after no treatment, 70% partial hepatectomy (PH), or selective portal vein embolization. The protocol consisted of the following sequences: three-dimensional-encoded spoiled gradient-echo sequence (repetition time per echo time 15 per 2.7 ms, flip angle 20°) for volumetry, and two-dimensional-encoded time-of-flight angiography sequence (repetition time per echo time 18 per 6.4 ms, flip angle 80°) for vessel visualization. Liver volume and portal vein segmentation was performed using a dedicated postprocessing software. In animals with portal vein embolization, portography served as reference standard. True liver volume was measured after sacrificing the animals. Measurements were carried out by two independent observers with subsequent analysis by the Cohen κ-test for interobserver agreement.

RESULTS

MRI liver volumetry highly correlated with the true liver volume measurement using a conventional method in both the untreated liver and the liver remnant after 70% PH with a high interobserver correlation coefficient of 0.94 (95% confidence interval, 0.80-0.98 for untreated liver [P < 0.001] and 0.90-0.97 after 70% PH [P < 0.001]). The diagnostic accuracy of magnetic resonance angiography for the occlusion of one branch of the portal vein was 0.95 (95% confidence interval, 0.84-1). The level of agreement between the two observers for the description of intrahepatic vascular anatomy was excellent (Cohen κ value = 0.925).

CONCLUSIONS

This protocol may be used for noninvasive liver volumetry and visualization of portal vein anatomy in mice. It will serve the dynamic study of new strategies to enhance liver regeneration in vivo.

Long-term assessment of contrast effects of gadofluorine M and gadofluorine P in magnetic resonance imaging of mice

PURPOSE

To investigate the long-term time course of the contrast effects after the intravenous injection of gadofluorine M or gadofluorine P in mice.

MATERIALS AND METHODS

Magnetic resonance images were acquired longitudinally after intravenous injection of 0.1 μmol Gd/g gadofluorine M into BALB/c mice. The contrast effects were also assessed in C57BL/6J mice injected with gadofluorine M, BALB/c mice injected with gadofluorine P, and BALB/c mice injected with a double dose of gadopentetate dimeglumine.

RESULTS

The injection of gadofluorine M into BALB/c mice caused prolonged contrast effects in the blood and other organs. The liver enhancement was especially long-lasting and still evident 6 days after injection. Strain-related differences in contrast kinetics of gadofluorine M were not observed between BALB/c mice and C57BL/6J mice. In comparison with gadofluorine M, clearances from the blood, liver, and kidney were more rapid and contrast enhancement in the spleen was generally lower for gadofluorine P. The enhancement in the gallbladder cavity, indicating biliary excretion, was evident only after gadofluorine P injection. Blood enhancement at 10 min was much weaker for gadopentetate dimeglumine.

CONCLUSION

Both gadofluorine M and gadofluorine P appear to be applicable to blood pool imaging and liver imaging in mice.

Effect of isoflurane anesthesia and hypothermia on the hepatic kinetics of Gd-EOB-DTPA: evaluation using MRI of conscious mice

PURPOSE

To develop a method for body magnetic resonance imaging (MRI) of conscious mice and investigate the effect of isoflurane anesthesia and hypothermia on the hepatic kinetics of gadoxetate disodium (Gd-EOB-DTPA).

MATERIALS AND METHODS

Conscious or anesthetized mice were restrained on a holder and the rectal temperature was measured serially. Serial MRI of the liver was performed after intravenous injection of Gd-EOB-DTPA with or without temperature control. Three mice were studied for each condition.

RESULTS

The temperature dropped rapidly in anesthetized mice beside the MR unit. The decline was less prominent in conscious mice. The temperature decreased less in anesthetized mice and remained constant in conscious mice in the radiofrequency (RF) coil. The washout of Gd-EOB-DTPA was slower in anesthetized hypothermic mice than in conscious normothermic mice. Warmed anesthetized mice showed faster washout, and cooled conscious mice showed delayed washout. Severer hypothermia in anesthetized mice resulted in weaker initial enhancement and slower washout.

CONCLUSION

By separately manipulating the presence or absence of anesthesia and hypothermia, we demonstrated that washout of Gd-EOB-DTPA was delayed under hypothermia, regardless of anesthesia. Serial body MRI of conscious mice was feasible and allowed the evaluation of kinetics of a contrast agent, while excluding the possible effects of anesthesia.

Diet and gastrointestinal signal on T1-weighted magnetic resonance imaging of mice

In magnetic resonance (MR) imaging of small animals, the gastrointestinal contents may give rise to intense signals on T1-weighted images. The aim of this study was to determine the optimal dietary preparation to reduce gastrointestinal signals in mice and to evaluate the usefulness of this approach. Images of the mouse trunk were obtained using a T1-weighted, three-dimensional fast low-angle shot sequence under various dietary conditions and were compared with respect to the gastrointestinal signals and image quality. The dietary preparation studied included giving alternative diets for 24 h, intestinal cleansing, and 6-h fasting. Mice with and without dietary preparation underwent MR lymphography using gadofluorine 8, and the visualization of abdominal lymph nodes was compared. In the absence of dietary preparation, hyperintense areas were conspicuous in the gastrointestinal system, whereas on the images taken from mice fed potato or sweet potato for 24 h before imaging, gastrointestinal hyperintensity was less prominent. This preparation also reduced artifactual signals and resulted in higher-quality images of the kidneys. Intestinal cleansing, which consisted of 24-h fasting and laxative intake, did not reduce the gastrointestinal signals and caused signal changes that were indicative of fatty liver development. Some of the abdominal lymph nodes of the mice that did not receive dietary preparation were visualized on MR lymphography source images but not on maximum intensity projection (MIP) images. In contrast, on the MIP images of mice fed potato, all the lymph nodes delineated on the source images were successfully visualized. In conclusion, feeding mice potato or sweet potato for 24 h before MR imaging reduces the gastrointestinal signals and image degradation due to artifacts. Appropriate dietary preparations facilitate the display of target structures on MIP images and are expected to enhance the capabilities of small animal MR imaging.