Imaging Characteristics of DHOG, a Hepatobiliary Contrast Agent for Preclinical MicroCT in Mice

Rationale and Objectives

This study was performed to assess the imaging characteristics and pharmacokinetics of 1,3-Bis-[7-(3-amino-2,4,6-triiodophenyl)-heptanoyl]-2-oleoyl glycerol (DHOG, Fenestra LC), a hepatobiliary contrast agent for microCT.

Materials and Methods

We investigated the abdomen of 18 female C3H mice in a MicroCAT II microCT scanner before contrast agent injection and at multiple time points up to 48 hours after intravenous injection of DHOG (1 g I/kg body weight). The contrast agent effect was determined quantitatively and dynamically by measuring pre- and postcontrast Hounsfield units (HU) of the liver, aorta, spleen, and kidneys. Based on additional phantom measurements, the reproducibility of lesion detection was estimated for different lesion sizes.

Results

DHOG caused a marked early postcontrast enhancement of blood in the aorta and a very high enhancement of the spleen, both slowly declined after 90 minutes. The liver parenchyma showed a slow contrast agent accumulation and clearly increased HU data between 3 and 7 hours after injection. No significant renal parenchymal enhancement or excretion was noticed. At early time points after administration, DHOG exhibits characteristics of a macromolecular contrast agent by demonstrating a blood pool effect. At later time points, DHOG provides a prolonged, marked liver enhancement on microCT images due to its specific liver uptake. For a lesion size of 1 mm diameter, the variability in between two scans was 27.7 HU ( P < .05) and the variability for different planes of one scan was 19.8 HU ( P < .05).

Conclusions

DHOG yields a very good visualization of the liver and delineation of the surrounding structures with a long plateau. It is a very suitable contrast agent for liver imaging in mice for microCT imaging. The presented protocol provides a high reproducibility for lesion detection with a relatively low radiation dose.

Animal models are essential to study diseases under highly controlled conditions in experimental studies. Imaging techniques provide a noninvasive tool to monitor the course of the evaluated disease, thereby allowing the evaluation of the same animal at different time points. This reduces both the number of animals needed and the overall cost. Clinical computed tomography (CT) scanners do not provide sufficient image quality to investigate small animals. Therefore specific CT scanners for imaging of animals have been designed and commercialized. MicroCT scanners provide a spatial resolution of up to 5 μm. However, one limitation of these systems is poor soft-tissue contrast. In addition, long acquisition times of these scanners preclude the use of standard water-soluble contrast agents, because the contrast enhancement does not persist through the entirety of a postcontrast scan. Therefore new CT-contrast agents have been developed that exhibit different pharmacokinetics like longer blood pool phases or receptor mediated uptake mechanisms, and thereby are more suitable for the long acquisition times of microCT scanners.

1,3-Bis-[7-(3-amino-2,4,6-triiodophenyl)-heptanoyl]-2-oleoyl glycerol (DHOG) (Fenestra LC, ART Inc., Saint Laurent, Quebec, Canada) is a hepatocyte-selective, commercially available, iodinated contrast agent ( ). The agent consists of a lipophilic iodinized triglyceride, which is formulated in a synthetic oil-in-water lipid emulsion particle that resembles a chylomicron remnant. DHOG’s structure and particle size of 90–180 nm is similar to the size of endogenous chylomicron remnants (75–400 nm), which allows for fast sequestration and receptor-mediated liver uptake. After intravenous injection, the particles distribute to the vasculature of the liver, pass through the endothelial fenestrations into the space of Disse, bind to the apoE-receptor on hepatocytes and are subsequently internalized into these cells ( ), and then excreted via the biliary system.

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Materials and methods

Contrast Agent

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Animals

Get Radiology Tree app to read full this article<

MicroCT Protocol

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Data Analysis

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Results

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Table 1

Standard Deviation of Hounsfield Unit Values Within One Scan (Intrascan) and in Between Subsequent Scans (Interscan) for Different Region of Interest Sizes

Lesion Diameter (mm) Standard Deviation (Hounsfield Unit) Intrascan Interscan 1 9.97 13.84 2 6.37 10.34 3 4.93 9.05

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Discussion

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

Get Radiology Tree app to read full this article<

References

• 1. Weichert J.P., Longino M.A., Bakan D.A., et. al.: Polyiodinated triglyceride analogs as potential computed tomography imaging agents for the liver. J Med Chem 1995; 38: pp. 636-646.

• 2. Cooper A.D.: Hepatic uptake of chylomicron remnants. J Lipid Res 1997; 38: pp. 2173-2192.

• 3. Masuno H., Shiosaka T., Itoh Y., et. al.: Hepatic triglyceride lipase and lipoprotein lipase activities in post-heparin plasma of patients with various cancers. Jpn J Cancer Res 1985; 76: pp. 202-207.

• 4. Weichert J.P., Longino M.A., Spigarelli M.G., et. al.: Computed tomography scanning of Morris hepatomas with liver-specific polyiodinated triglycerides. Acad Radiol 1996; 3: pp. 412-417.

• 5. Weichert J.P., Lee F.T., Longino M.A., et. al.: Lipid-based blood-pool CT imaging of the liver. Acad Radiol 1998; 5: S16S9; discussion S28–S30

• 6. Bakan D.A., Longino M.A., Weichert J.P., et. al.: Physicochemical characterization of a synthetic lipid emulsion for hepatocyte-selective delivery of lipophilic compounds: application to polyiodinated triglycerides as contrast agents for computed tomography. J Pharm Sci 1996; 85: pp. 908-914.

• 7. Longino M.A., Bakan D.A., Weichert J.P., et. al.: Formulation of polyiodinated triglyceride analogues in a chylomicron remnant-like liver-selective delivery vehicle. Pharm Res 1996; 13: pp. 875-879.

• 8. Lee F.T., Chosy S.G., Naidu S.G., et. al.: CT depiction of experimental liver tumors: contrast enhancement with hepatocyte-selective iodinated triglyceride versus conventional techniques. Radiology 1997; 203: pp. 465-470.

• 9. Ford N.L., Thornton M.M., Holdsworth D.W.: Fundamental image quality limits for microcomputed tomography in small animals. Med Phys 2003; 30: pp. 2869-2877.

• 10. Desser T.S., Rubin D.L., Muller H.H., et. al.: Dynamics of tumor imaging with Gd-DTPA-polyethylene glycol polymers: dependence on molecular weight. J Magn Reson Imaging 1994; 4: pp. 467-472.

• 11. Simon G.H., Fu Y., Berejnoi K., et. al.: Initial computed tomography imaging experience using a new macromolecular iodinated contrast medium in experimental breast cancer. Invest Radiol 2005; 40: pp. 614-620.

• 12. Roberts T.P.: Physiologic measurements by contrast-enhanced MR imaging: expectations and limitations. J Magn Reson Imaging 1997; 7: pp. 82-90.

• 13. Bakan D.A., Lee F.T., Weichert J.P., et. al.: Hepatobiliary imaging using a novel hepatocyte-selective CT contrast agent. Acad Radiol 2002; 9: pp. S194-S1949.

• 14. Violante M.R., Dean P.B., Fischer H.W., et. al.: Particulate contrast media for computed tomographic scanning of the liver. Invest Radiol 1980; 15: pp. S171-S175.

• 15. Cassel D.M., Young S.W., Brody W.R., et. al.: Radiographic blood pool contrast agents for vascular and tumor imaging with projection radiography and computed tomography. J Comput Assist Tomogr 1982; 6: pp. 141-146.

• 16. Mattrey R.F., Long D.M., Peck W.W., et. al.: Perfluoroctylbromide as a blood pool contrast agent for liver, spleen, and vascular imaging in computed tomography. J Comput Assist Tomogr 1984; 8: pp. 739-744.

• 17. Rummeny E.J., Berning W., Fuest M., et. al.: New RES-specific contrast agents for CT. Acad Radiol 2002; 9: pp. S185-S190.

• 18. Mukundan S., Ghaghada K.B., Badea C.T., et. al.: A liposomal nanoscale contrast agent for preclinical CT in mice. AJR Am J Roentgenol 2006; 186: pp. 300-307.

• 19. Vera D.R., Mattrey R.F.: A molecular CT blood pool contrast agent. Acad Radiol 2002; 9: pp. 784-792.

• 20. Torchilin V.P., Frank-Kamenetsky M.D., Wolf G.L.: CT visualization of blood pool in rats by using long-circulating, iodine-containing micelles. Acad Radiol 1999; 6: pp. 61-65.