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

Abstract

Background: Local hyperthermia has been shown to be an effective adjuvant therapy for cancer. However, progress in this treatment modality requires the 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-invasively and three-dimensionally, temperature distribution within tumours. An animal model taking into account the complex interrelationship between pathophysiological changes within a tumour during hyperthermia and temperature-sensitive MR parameters is warranted for the development and validation of new MR thermometry technology. Methods: An experimental set-up was implemented to allow simultaneous measurements of temperature, tumour blood flow and temperature-sensitive MR parameters under standardised conditions in vivo. Local hyperthermia was induced at 44°C for 20 min under inhalation anaesthesia on seven Syrian Golden hamsters bearing an amelanotic melanoma. Fibreoptic probes were used for reference temperature measurements. Laser Doppler flowmetry served for on-line tumour blood flow determination, and MR thermometry was performed using longitudinal T1 relaxation time measurements. Results: The experimental design enables multifunctional MR thermometry. T1 relaxation times of tumours were 1.44 s (1.36, 1.46) and 1.53 s (1.48, 1.75) at 37°C and during hyperthermia at 44°C, respectively (median, 25% and