OBJECTIVE Minimally invasive procedures may allow surgeons to avoid conventional open surgical procedures for certain neurological disorders. This paper describes the iterative process for development of a catheter-based ultrasound thermal therapy applicator. METHODS Using an ultrasound applicator with an array of longitudinally stacked and angularly sectored tubular transducers within a catheter, the authors conducted experimental studies in porcine liver, in vivo and ex vivo, in order to characterize the device performance and lesion patterns. In addition, they applied the technique in a rodent model of Parkinson's disease to investigate the feasibility of its application in brain. RESULTS Thermal lesions with multiple shapes and sizes were readily achieved in porcine liver. The feasibility of catheter-based focused ultrasound in the treatment of brain conditions was demonstrated in a rodent model of Parkinson's disease. CONCLUSIONS The authors show proof of principle of a catheter-based ultrasound system that can create lesions with concurrent thermode-based measurements.