Validation of MR thermometry technology: a small animal model for hyperthermic treatment of tumours

Background: Local hyperthermia has been shown to be an effective adjuvant t herapy for cancer. However, progress in this treatment modality requires th e non-invasive assessment of temperature distribution in the entire tumour to enable administration of an efficient thermal dose to all tumour areas. Magnetic resonance (MR) imaging offers a promising tool to quantify, non-in vasively and three-dimensionally temperature distribution within tumours. A n animal model taking into account the complex interrelationship between pa thophysiological changes within a tumour during hyperthermia and temperatur e-sensitive MR parameters is warranted for the development and validation o f new MR thermometry technology. Methods: An experimental set-up was implem ented to allow simultaneous measurements of temperature, tumour blood flow and temperature-sensitive MR parameters under standardised conditions in vi vo. Local hyperthermia was induced at 44 degrees C for 20 min under inhalat ion anaesthesia on seven Syrian Golden hamsters bearing an amelanotic melan oma. Fibreoptic probes were used for reference temperature measurements. La ser Doppler flowmetry served for on-line tumour blood flow determination, a nd MR thermometry was performed using longitudinal T1 relaxation time measu rements. Results: The experimental design enables multifunctional MR thermo metry. T1 relaxation times of tumours were 1.44 a (1.36, 1.46) and 1.53 s ( 1.48, 1.75) at 37 degrees C and during hyperthermia at 44 degrees C, respec tively (median, 25% and 75% quartiles, respectively; P<0.05). At the end of 20 min of hyperthermic treatment at 44 degrees C, relative tumour blood fl ow was reduced to 40.5% (20.7, 43.3) compared to values before treatment (m edian, 25% and 75% quartiles, respectively; P<0.05). Imaging of TI relaxati on times revealed a heterogeneous distribution in temperature during hypert hermic treatment. Conclusion: This novel in vivo model allows standardised investigations for the development and validation of MR thermography method s.