Design and characterization of a laterally mounted phased-array transducer breast-specific MRgHIFU device with integrated 11-channel receiver array.

PURPOSE: This work presents the design and preliminary evaluation of a new laterally mounted phased-array MRI-guided high-intensity focused ultrasound (MRgHIFU) system with an integrated 11-channel phased-array radio frequency (RF) coil intended for breast cancer treatment. The design goals for the system included the ability to treat the majority of tumor locations, to increase the MR image's signal-to-noise ratio (SNR) throughout the treatment volume and to provide adequate comfort for the patient. METHODS: In order to treat the majority of the breast volume, the device was designed such that the treated breast is suspended in a 17-cm diameter treatment cylinder. A laterally shooting 1-MHz, 256-element phased-array ultrasound transducer with flexible positioning is mounted outside the treatment cylinder. This configuration achieves a reduced water volume to minimize RF coil loading effects, to position the coils closer to the breast for increased signal sensitivity, and to reduce the MR image noise associated with using water as the coupling fluid. This design uses an 11-channel phased-array RF coil that is placed on the outer surface of the cylinder surrounding the breast. Mechanical positioning of the transducer and electronic steering of the focal spot enable placement of the ultrasound focus at arbitrary locations throughout the suspended breast. The treatment platform allows the patient to lie prone in a face-down position. The system was tested for comfort with 18 normal volunteers and SNR capabilities in one normal volunteer and for heating accuracy and stability in homogeneous phantom and inhomogeneous ex vivo porcine tissue. RESULTS: There was a 61% increase in mean relative SNR achieved in a homogeneous phantom using the 11-channel RF coil when compared to using only a single-loop coil around the chest wall. The repeatability of the system's energy delivery in a single location was excellent, with less than 3% variability between repeated temperature measurements at the same location. The execution of a continuously sonicated, predefined 48-point, 8-min trajectory path resulted in an ablation volume of 8.17 cm(3), with one standard deviation of 0.35 cm(3) between inhomogeneous ex vivo tissue samples. Comfort testing resulted in negligible side effects for all volunteers. CONCLUSIONS: The initial results suggest that this new device will potentially be suitable for MRgHIFU treatment in a wide range of breast sizes and tumor locations.

Mobile Navigation Using Haptic, Audio, and Visual Direction Cues with a Handheld Test Platform.

This paper reports on a series of user experiments evaluating the design of a multimodal test platform capable of rendering visual, audio, vibrotactile, and directional skin-stretch stimuli. The test platform is a handheld, wirelessly controlled device that will facilitate experiments with mobile users in realistic environments. Stimuli rendered by the device are fully characterized, and have little variance in stimulus onset timing. A series of user experiments utilizing navigational cues validates the function of the device and investigates the user response to all stimulus modes. Results show users are capable of interpreting all stimuli with high accuracy and can use the direction cues for mobile navigation. Tests included both stationary (seated) and mobile (walking a simple obstacle course) tasks. Accuracy and response time patterns are similar in both seated and mobile conditions. This device provides a means of designing and evaluating multimodal communication methods for handheld devices and will facilitate experiments investigating the effects of stimulus mode on device usability and situation awareness.