Tomographic fluorescence imaging of tumor vascular volume in mice.
OBJECTIVE
To prospectively determine the feasibility of imaging vascular volume fraction (VVF) and its therapeutic inhibition in mouse models of cancer with three-dimensional fluorescence molecular tomography (FMT).


METHODS
All studies were approved by the institutional animal review committee and were in accordance with National Institutes of Health guidelines. CT26 colon tumor-bearing mice were imaged with FMT after intravenous administration of long-circulating near-infrared fluorescent blood-pool agents optimized for two nonoverlapping excitation wavelengths (680 and 750 nm). A total of 58 mice were used for imaging VVF to evaluate the following: (a) differences in ectopically and orthotopically implanted tumors (n = 10), (b) cohorts of mice (n = 24) treated with anti-vascular endothelial growth factor (VEGF) antibody, (c) serial imaging in same animal to determine natural course of angiogenesis (n = 4), and (d) dose response to anti-VEGF therapy (n = 20). To compare groups receiving antiangiogenic chemotherapy, analysis of variance was used.


RESULTS
Fluorochrome concentrations derived from FMT measurements were reconstructed with an accuracy of +/-10% at 680 nm and +/-7% at 750 nm and in a depth-independent manner, unlike at reflectance imaging. FMT measurements of vascular fluorescent probes were linear, with concentration over several orders of magnitude (r > 0.98). VVFs of colonic tumors, which varied considerably among animals (3.5% +/- 1.5 [standard deviation]), could be depicted with in vivo imaging in three dimensions with less than 5 minutes of imaging and less than 3 minutes of analysis. The natural course of angiogenesis and its inhibition could be reliably imaged and depicted serially in different experimental setups.


CONCLUSIONS
FMT is a tomographic optical imaging technique that, in conjunction with appropriate fluorescent probes, allows quantitative visualization of biologic processes.
Montet
Xavier
X
Center for Molecular Imaging Research, Massachusetts General Hospital and Harvard Medical School, Building 149, 13th St, Room 5403, Charlestown, MA 02129, USA.
Figueiredo
Jose-Luiz
JL
Alencar
Herlen
H
Ntziachristos
Vasilis
V
Mahmood
Umar
U
Weissleder
Ralph
R
D000818:Animals; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000098:blood supply* / Q000473:pathology*; D007089:Image Enhancement / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D051379:Mice; D008819:Mice, Nude; D008856:Microscopy, Fluorescence / Q000379:methods*; D009389:Neovascularization, Pathologic / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D041622:Tomography, Optical / Q000379:methods*