Statistical Tracking of Murine Liver Metastases using aHepatocyte-Selective Contrast Agent in Conjunction with MicroCT
142331,2BY Durkee , T Ton , MA Longino , C Qi , SM Weber , JP Weichert
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Departments of Medical Physics, Radiology, Surgery at University of Wisconsin, Madison and Alerion Biomedical, Inc.

Introduction

Procedure

Recent reports from our lab have shown that ITG, anFive mice were inoculated with 5e5 CT26 tumor cells (50 uL

iodinated hepatocyte-selective contrast agent, used inby volume) by direct splenic injection (Figure 1). The miceconjunction with microCT is an effective method for identifying

Locus, 80 kVp, 93 um resolution).

This study aims to improve upon the method of quantifyingisoflurane) was used during the inoculation and during each

eventually treatment) serially in living mice.

scan.

Soft Tissue

Lungs

between progression of liver metastases and the standard
Bonedeviation of a peak representing liver contrast agent.

Gas anesthetic (1.5%

The mice were euthanized at day 9 for grosspathological inspection.

The results of this pilot study show the likelihood of correlation

Fatwere scanned at days 0, 4, and 8 with microCT (GE eXplore

and roughly quantifying hepatomas in murine tumor models.
net tumor volume and also to track tumor growth (andDiscussionAir

Each scan was enhanced by theThe broader implication of this study is that it may be possible

Figure 3: Histogram (frequency) of voxel densities in amouse microCT volume. No was contrast used.

to track metastatic progression despite the fact that themetastases are too small to resolve, or too many to count.

contrast agent FenestraTM LC (0.3 mL/20 g bw), injected by
In studies of live mice without contrast, a histogram of voxel

tail vein four hours prior to scan.

AirAlthough it is impossible to establish statistical significancedensities consistently generates four identifiable peaks(Figure 3). Analysis by selective regions of interest (ROI’s)
matches these peaks to air, lungs, soft tissue, and bone. A
retrospective study of 12 mice has shown that in each caseFenestraTM LC

Using MicroView (GE Healthcare, Waukesha, WI), a
volumetric ROI was defined to include the entire liver (Figureanalysis to detect sub-resolution changes may have

Soft TissueLungs

Bone2). A histogram of the ROI was rendered (Figure 3), making it

there is an additional peak when ITG was present (Figure 4).

possible to easily identify the peak associated withThis study will utilize FenestraTM LC (Alerion Biomedical Inc.,

FenestraTM,San Diego, CA), the novel commercial anologue of ITG.

Fatand analyze the peak using the built-in Bone

Mineral Density tool.

Mean peak values and standard

with only five mice, this technique of using numerical peakinteresting implications in medical imaging.

One notable

example might be the ability to track progression andtreatment of angiogenesis, despite the fact that many
Figure 4: Histogram of volume acquired 4 hours after 0.3 mL
Fenestra injected. Calculated standard deviation of peak isangiogenic vessels are beyond the resolution of the scanner.

deviations were assessed for each mouse over the eight-day
Preliminary studies in a single mouse have shown that liver

scanning period. To verify that the range of the peak includes

volume can accurately be assessed by calculating the area

the liver, MicroView has a tool that allows the user to highlightunder the ITG peak by integration, and multiplying the result

the corresponding voxel values in the image.

by voxel size. A comparison of two such calculations (in-vivo

recorded were averaged and plotted on a relative scale fromand ex-vivo liver) shows good precision (<10% error) in this0 to 1.

The values

method.
1. CT 26 tumor
cells injected
into spleen

Results

Key References

The standard deviation of the voxel densities in the liver
showed marked increase (average ~50 HU SD) over the eight
day period (Figure 5). While five mice is not enough to show
statistical significance, correlation between metastatic
progression and increased standard deviation in tissue
density with contrast.
Relative Standard Deviation ofContrast Enhanced Liver

2. Cells
metastasize
in liver1.2[1] Weichert JP, et al., Radiology (2000) 216:865-871.
[2] Weichert JP, et al., J Med Chem (1995) 38:636-646.
[3] Paulus MJ, Gleason SS, Kennel SJ, Hunsicker PR,
Johnson DK.
High-resolution x-ray computed
tomography: An emerging tool for small animal cancer
research. Neoplasia 2000; 2(1-2):62-70.
[4] Paulus MJ, Gleason SS, Easterly ME. A review of highresolution x-ray computed tomography and otherimaging modalities for small animal research. Lab Animal
2001; 30(3):1-10.
[5] Holdsworth DW, Thornton MM.
MicroCT in small
animal and specimen imaging. Trends in Biotechnology
2002; 20(8):S34-S39 (suppl.).

Standard Deviation (Relative)

10.8
0.6
0.4
0.2
0Day 0Figure 1: MicroCT of mouse abdomen with GE eXplore
Locus RS at 93 micron resolution.

Figure 2: 3D ROI selection in MicroView. ROI includes the entire liver.

Day 4Day 8Figure 5: Standard deviation of voxel densities increased overa period of eight days.

The authors would like toacknowledge GE Healthcare PreClinical Imaging, Alerion
Biomedical, Chad Griffith, andMO. The authors would also
like to thank Siemens Medical
Solutions for the SMI TravelGrant.