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Selective laser-tissue interaction is a promising method for noninvasive treatment of deep tumors. Using a laser beam with a wavelength in the near-infrared region and an intratumoral injection of a laserabsorbing dye, the laser energy can destroy targeted tumor cells while sparing normal surrounding tissue. Introducing an immunoadjuvant can achieve possible systemic antitumor immune response, hence augmenting the selective laser-tissue interaction. Administration of the dye and the immunoadjuvant, and the time window for optimal laser application, are crucial in determining the outcome of the treatment. To determine the dynamic distribution of intratumor-injected laser-absorbing dye and immunoadjuvant, a digital x-ray imaging technique was employed. Indocyanine green as the laser-absorbing dye and glycated chitosan as the immunoadjuvant were injected into the center of a rat tumor, and the transmitted x-ray signals through tumor tissue and surrounding normal tissue, before and after the injection, were acquired and analyzed. The transmitted signals through tissue were reduced due to the injection of either dye or immunoadjuvant solution. The diffusion of aqueous solutions in tissue was a function of time and of the properties of the solutes. The indocyanine green solution, due to its low molecular weight, diffused through the tumor almost immediately after injection, then gradually dispersed into the surrounding tissue. The glycated chitosan, on the other hand, due to its high molecular weight and high viscosity, dispersed slowly and took about 20 to 25 min to reach maximum accumulation at the edge of the tumor. Our results showed that the digital x-ray images could be used to guide the precise positioning of the injecting needle, and to determine the distributions of the dye and immunoadjuvant in the tumor and in the surrounding normal tissue. Apparently, the dynamic observation of dye and immunoadjuvant administration and their diffusion process could be used to optimize the parameters for laser treatment of deep tumors.
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