Noninvasive vascular spectral unmixing

Accurate and noninvasive imaging of tumor vascularization in live animals has been done so far with fluorescently labeled vascular probes. Tumor blood vessels, however, often have poor integrity, resulting in the leakage of the vascular probes into the tumor. If the probe half-life is long and there is poor clearance of the probe from the tumor, then the fluorescent signal in the tumor would no longer be restricted to tumor blood vessels. P. Mayes and colleagues in the laboratory of W. El-Deiry at the University of Pennsylvania School of Medicine (Philadelphia, PA) have abandoned vascular probes through the multispectral imaging of reporter genes in fluorescent tumors.

By multispectral imaging they examined a tumor expressing red fluorescent protein (dsRed from Clontech), a clear 10-nm upward shift in wavelength was associated with the spectral emission signature of tumor blood vessels relative to the fluorescent tumor tissue. This spectral unmixing technique could image 10-µm diameter tumor capillaries. In a small pilot study of antiangiogenic therapy on the fluorescent tumors, spectral unmixing detected a decrease in tumor vascularization over one week, which was verified by immunohistochemistry. It is worth to note that such event was not observed with a vascular probe, thereby demonstrating the superiority of spectral unmixing and of genetic markers in general when coupled to noninvasive imaging.

Patrick Mayes, David Dicker, Yingqiu Liu, Wafik El-Deiry (2008). Noninvasive vascular imaging in fluorescent tumors using multispectral unmixing BioTechniques, 45 (4), 459-464 DOI: 10.2144/000112946