MR imaging of laser-tissue interactions.

A new application of magnetic resonance (MR) imaging to map the spatial and temporal distribution of the effects of Nd:YAG lasers on tissues was studied. The temperature dependence of MR relaxation mechanisms and the high sensitivity of MR to changes in the mobility and distribution of tissue water make it particularly suitable for the demonstration and control of thermal energy deposition in tissues. In heterogeneous tissues, MR imaging does not follow changing temperatures directly because even in the case of reversible thermal interactions, there is a hysteresis in the dynamic relationship between MR signal intensity and temperature. Appropriate matching of the laser and MR pulse sequences can, however, optimize the detection of relatively small laser energy deposition, and reversible and irreversible tissue changes can be distinguished. There is a potential for the integration of MR imaging and lasers for three-dimensional control and monitoring of laser-tissue interactions.