Image-guided spectroscopy of cancer: Translating optical technology into clinical tools

Integration of localized molecular spectroscopy into standard medical imaging instrumentation has been slow in developing, yet today there have been major developments which make it achievable on a routine basis. Perhaps the most striking thing about optical imaging is the incredibly wide range of technologies available, and the correspondingly large range of resolutions in which they target, from microscopic imaging at 1 micron resolution, upto macroscopic imaging with 1-5mm resolution. The choice of technology must be done for the application desired. In cancer diagnosis and therapy monitoring, MR spectroscopy of tumors is done routinely in some centers, and the potential for near-infrared spectroscopy (NIRS) is also available. The American College of Radiology Imaging Network (ACRIN) has sponsored the first multicenter trial in NIRS to track response to neoadjuvant chemotherapy for breast cancer. NIRS can also be combined with image-guided recovery of the tissue components, using standard MR images, to quantify the spectroscopic features of breast cancer. A prototype system integrating NIRS into a 3T MR breast coil is outlined, and the ongoing study using the MR image as the template upon with spectroscopy is completed will be presented, with results from neoadjuvant chemotherapy monitoring. In radiology research, two prototype systems broadband spectral imaging of tissue are discussed, and it is shown that the spectral tomography system is ideal for fluorescence or emission tomography in vivo. This type of hybrid imaging is still in its infancy, yet using it to guide therapy or to properly individualize therapy choice is the next logical step. Use of MRI or CT as the backbone technology to exploit NIRS is a logical step for integration of this modality into clinical use. Imaging of molecular features is provided by this approach, such as Raman vibrational fingerprint of bone tissue, and uptake of multiple exogenous fluorescent agents in the same subject. Additional examples of how emission tomography could guide radiation therapy are demonstrated. In imaging for surgical guidance, molecular tracers such as Epidermal Growth Factor and Protoporphyrin IX are shown to be increased in glioma tumors, and are providing actually superior detection of the tumor tissue using standard white light surgical guidance. The state of the art in fluorescence guidance of surgery will be discussed, as well as future directions looking for peptide markers which could be translated to other tumor organ sites.