Real time monitoring of laser-induced thermal changes in cartilage in vitro by using snapshot FLASH

Snapshot FLASH imaging has been applied to study the spatial and temporal spreading of thermal changes caused by a Holmium:YAG laser in patella cartilage in vitro at 7 T. The temperature dependence of the proton resonance frequency was used to demonstrate the thermal energy deposition. A series of cartilage images, with a time resolution of 512 ms and a spatial resolution of 400 x 200 microm, showed dynamic changes of the temperature-related image phase in the regions irradiated by the laser.

[Magnetic resonance imaging and temperature measurement in cartilage following laser therapy]

The aim of this study was the dynamic measurement, with magnetic resonance imaging, of temperature in cartilage irradiated by laser. Fresh specimens, each with chondromalacia grade II and III, were irradiated with a Holmium:YAG laser under MRI control. Temperature was measured by means of the proton-shift method, which allows high temporal and spatial resolution. With this method a maximum increase in temperature of 35 degrees was found after irradiation with 1.0 J and 10 Hz for 5 s at a distance of 1 mm. In no case at all was an increase in temperature of more than 10 degrees observed in the cartilage adjacent to the subchondral bone. These results exclude the possibility of significant thermal damage from laser treatment as described.