Near-infrared optical imaging of protease activity for tumor detection

Radiology. 1999 Dec;213(3):866-70. doi: 10.1148/radiology.213.3.r99dc14866.


Purpose: To build and test an optical imaging system that is sensitive to near-infrared fluorescent molecular probes activated by specific enzymes in tumor tissues in mice.

Materials and methods: The imaging system consisted of a source that delivered 610-650-nm excitation light within a lighttight chamber, a 700-nm longpass filter for selecting near-infrared fluorescence emission photons from tissues, and a charge-coupled device (CCD) for recording images. The molecular probe was a biocompatible autoquenched near-infrared fluorescent compound that was activated by tumor-associated proteases for cathepsins B and H. Imaging experiments were performed 0-72 hours after intravenous injection of the probe in nude mice that bore human breast carcinoma (BT-20).

Results: The imaging system had a maximal spatial resolution of 60 microns, with a field of view of 14 cm2. The detection threshold of the nonquenched near-infrared fluorescent dye was subpicomolar in the imaging phantom experiments. In tissue, 250 pmol of fluorochrome was easily detected during the 10-second image acquisition. After intravenous injection of the probe into the tumor-bearing animals, tumors as small as 1 mm became detectable because of tumor-associated enzymatic activation of the quenched compound.

Conclusion: Tumor proteases can be used as molecular targets, allowing visualization of millimeter-sized tumors. The development of this technology, probe design, and optical imaging systems hold promise for molecular imaging, cancer detection, and evaluation of treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma / diagnosis
  • Animals
  • Cathepsin B / analysis
  • Cathepsin H
  • Cathepsins / analysis
  • Cysteine Endopeptidases / analysis
  • Endopeptidases / analysis*
  • Female
  • Humans
  • Image Processing, Computer-Assisted
  • Male
  • Mammary Neoplasms, Experimental / diagnosis
  • Mice
  • Mice, Nude
  • Neoplasm Transplantation
  • Neoplasms / diagnosis*
  • Phantoms, Imaging
  • Spectroscopy, Near-Infrared / instrumentation*
  • Tumor Cells, Cultured


  • Cathepsins
  • Endopeptidases
  • Cysteine Endopeptidases
  • Cathepsin B
  • CTSH protein, human
  • Cathepsin H
  • Ctsh protein, mouse