Multisectored Ultrasound Applicators for Thermal Therapy

Heat treatments can be used as an adjunct to radiotherapy or chemotherapy or as a stand-alone alternative to surgery. Despite the therapeutic effects of heat, acceptance of thermal therapy in the clinic has been slow because of a lack of accurate control of heating distributions. Many different types of heating modalities and devices have been developed to deliver thermal therapy. Recent advancements in non-invasive temperature monitoring, in particular, MR, give an increased understanding of the spatial deposition of heat delivery in tissue. Ultrasound offers excellent spatial energy deposition and increased heating penetration due to its short wavelength. External, intracavitary, and interstitial ultrasound heating devices can deliver accurate thermal treatments when coupled with MR temperature monitoring. This work presents the development and evaluation of novel interstitial and transurethral ultrasound thermal therapy applicators designed for use with MR temperature monitoring. Multisectored tubular ultrasound transducers were developed and incorporated into the devices to deliver conformal thermal treatments in the angular and radial dimensions. To provide three dimensional control of the heating distribution, multiple multisectored transducers were incorporated along the length of the applicators. The devices were constructed of MR compatible materials and do not require any movement or manipulation during treatment to deliver a conformal heating distribution. Acoustic characterization of the multisectored ultrasound applicators was conducted using force-balance acoustic efficiency measurements and rotational acoustic beam profiles. In this work, 2D and 3D biothermal models were modified and developed to evaluate the heating characteristics of these devices. For verification of the model and thermal lesion evaluation, ex vivo tissue studies were completed. Finally, in vivo experiments under MR guidance and MR temperature monitoring were conducted in canine thigh muscle for the interstitial devices and canine prostate for the transurethral applicators. The in vivo studies displayed the ability of multisectored ultrasound applicators to conform thermal therapy to a target area during treatment according to feedback from MR temperature images and. This work details the design, development, biothermal model characterization, ex vivo tissue evaluation, and in vivo MR guided evaluation of novel multisectored ultrasound devices and outlines their potential for improving thermal therapy