| One of the major challenges in the field of cancer treatment is to induce a prolonged systemic immune response. Laser immunotherapy has shown its potential as a minimally invasive alternative for many cancer patients due to its ability to target and destroy cancerous cells while leaving minimal damage to surrounding tissue. Temperature distribution is a crucial factor during laser-tissue interaction in the treatment of tumors. In order to optimize laser immunotherapy, it is important to monitor the temperature distribution in target tissue during laser irradiation. Among the currently available temperature measurement techniques, Magnetic Resonance Thermometry (MRT) is the only feasible method for non-invasive, real-time, three-dimensional temperature mapping. In this study, we investigated the temperature distribution in gel phantom during laser irradiation using MRT. Spherical gel phantoms, as targets containing a light-absorbing agent, indocyanine green (ICG), of different concentrations were embedded inside normal phantom gels or in chicken breast tissue and were irradiated by an 805 nm diode laser. A 7.1 Tesla magnetic resonance imaging (MRI) system and a specially designed algorithm were used for ex vivo temperature mappings. The MRI signals were recorded using a fast low-angle shot (FLASH) sequence during laser irradiation with different values of MRI parameters such as TE (echo time), TR (repetition time), and NEX (number of excitation). The relative position of the proton, as determined by its phase, was obtained from the MRI signal. The phase data were reconstructed to obtain temperature distributions. Temperature elevation of target gels containing 0.056% ICG irradiated with laser of 2.0 watt/cm2 power density showed better selectivity compared to that of 0.08% and 0.10% ICG. However, phantom gels in chicken breast tissue with 0.08% ICG treated with laser of 1.0 watt/cm2 power density showed a considerable temperature elevation in the range of 10-35oC. Our results suggest that the effectiveness of the photothermal treatment depends on various parameters such as laser power, dye concentration, time of laser irradiation, and time of relaxation. This study provided important information for optimizing laser immunotherapy.;Key Words: Cancer treatment, laser immunotherapy, magnetic resonance thermometry (MRT), magnetic resonance imaging (MRI), indocyanine green (ICG), gel phantoms, fast low-angle shot (FLASH), TE (echo time), TR (repetition time), NEX (number of excitation), temperature mapping. |
