Thermal therapies in interventional MR imaging. Cryotherapy.

Cryotherapy of the brain is an old and well-established technique of functional and resective neurosurgery. With the use of modern imaging techniques such as MR imaging, which is ideally suited for diagnosis, planning, and monitoring of an ablation procedure, cryotherapy can become a modern alternative to other ablation techniques. In contrast to hyperthermal ablation tools such as laser or radiofrequency ablation, cryotherapy has specific potentials. First and most importantly, the freezing process ideally can be precisely monitored by MR imaging during the procedure without any specific temperature-sensitive pulse sequence. As shown in the experimental study, several techniques including conventional gradient echo sequences, ultrafast subsecond MR sequences, and MR fluoroscopy, are suited for monitoring the freezing process. Furthermore, the volume of the damaged tissue, as imaged by MR imaging, does not increase after completion of the ablation procedure. The extension of the ice corresponds well to the final, histologically confined necrosis and allows a high predictability of the resulting necrosis. Although not yet in clinical use, the combination of minimally invasive modern cryotherapy devices and ultrafast interventional MR techniques offer a promising alternative to other ablation techniques. In addition, it holds great promise for minimally invasive neurologic procedures in the near future. Further technical modifications and clinical studies, however, are necessary to establish the potential of this new treatment option.