Possible usefulness of light imaging in radiology. Comparison with other modalities

Described are the present state of in vivo imaging modalities for diagnosis and treatment of malignant tumors (MT) like prostate cancer (PC), and possible future usage of light for imaging. For diagnosis and treatment planning of PC, the author uses MRI of the diffusion weighted imaging, apparent diffusion coefficients mapping, MR Spectroscopy (MRS) imaging and perfusion imaging utilizing the endorectal coil (endorectal MRI). In MRS, metabolic signals are given at citrate (2.6 ppm), creatine (3.0) and choline (3.2), where higher choline peak is observable in MT, but long acquisition time, insufficient spatial resolution and low detectability of low grade malignancy are problematic. For this, molecular imaging with light is thought promising, which targets receptors of folate and beta-D-galactose. Light imaging has an advantage of high spatial resolution to detect the lesion of <1 mm, of which detection is difficult by the ordinary MRI, CT, PET and single photon emission computed tomography (SPECT): exempli gratia (e.g.), an experimental in vivo spectral fluorescence imaging of peritoneal cancer implants is suggested at submillimeter level with a lectin-targeted optical agent. Targeting to specific cells and molecules is possible using the targeting moiety like their antibody and if an activatable probe is available, the behavior of the probe can be traced outside and inside the cell depending on such an environment as changes of pH. Avidin-rhodamine X is an example of the probe. Gamma H2AX is a marker of DNA double strand break, and when it can be used as a light imaging agent to detect the DNA damage in the rectum at radiotherapy of PC, the agent will be useful to protect the rectal disorder caused by the late effect of the therapy. Clinical application of light imaging is thought to become more important in the future radiological field. (T.T.)