Temperature dosimetry using MR relaxation characteristics of poly(vinyl alcohol) cryogel (PVA-C)

Hyperthermic therapy is being used for a variety of medical treatments, suc h as tumor ablation and the enhancement Of radiation therapy. Research in t his area requires a tool to record the temperature distribution created by a heat source, similar to the dosimetry gels used in radiation therapy to r ecord dose distribution. Poly(vinyl alcohol) cryogel (PVA-C) is presented a s a material capable of recording temperature distributions between 45 and 70 degreesC, with less than a VC error. An approximately linear, positive r elationship between MR relaxation times and applied temperature is demonstr ated, with a maximum of 16.3 ms/degreesC change in T-1 and 10.2 ms/degreesC in T-2 for a typical PVA-C gel. Applied heat reduces the amount of cross-l inking in PVA-C, which is responsible for a predictable change in T-1 and T -2 times. Temperature distributions in PVA-C volumes may be determined by m atching MR relaxation times across the volumes to calibration values produc ed in samples subjected to known temperatures. Factors such as thermotolera nce, perfusion effects, and thermal conductivity of PVA-C are addressed for potentially extending this method to modeling thermal doses in tissue. (C) 2001 Wiley-Liss, Inc.