Control system for an MRI compatible intracavitary ultrasound array for thermal treatment of prostate disease

A 16-channel ultrasound intracavitary array is currently being used in a clinical setting for localized hyperthermia treatment of prostate tumours. Currently, the individual power to each array element is adjusted based on the clinician's judgement of the temperature measured at the locations of invasive thermocouple probes. MRI-derived temperature measurements may be useful for a feedback control system that non-invasively regulates the temperature distribution by adjusting the power to the elements of the array. MRI has been shown to provide accurate, high resolution, non-invasive thermometry. A proportional-plus-integral, single-input, single-output controller was designed to evaluate the feasibility of MRI-derived temperature feedback with this applicator. Input parameters for the controller were determined by modelling the tissue response to the heating from the array. Ex vivo and in vivo experiments evaluated the ability of the MRI-based temperature feedback control system to achieve and maintain a target temperature for a sustained period similar to that of a clinical hyperthermia treatment. With the controller set to a reference temperature of 43 degreesC and a rise time of 6 min, the temperatures within the ex vivo tissue (n = 6) were 43.1 +/- 0.3 degreesC after reaching the reference temperature and had a rise time of 9.5 +/- 0.3 min. In vivo results using rabbit thigh muscle (n = 7) showed that the steady state temperatures were within +/- 1 degreesC of their target temperatures. These results demonstrated the feasibility of a temperature feedback for controlling the heating from an intracavitary transrectal array based on temperature information from MR images.