MR acoustic radiation force ͑ARF͒ imaging was developed for measuring tissue elastic properties using focused ultrasound to deliver a localized tissue motion. In this study, an imaging ultrasound transducer was mounted on the focused ultrasound transducer and ultrasound motion tracking was performed simultaneously to MR ARF imaging to validate the measurement results. In vivo studies on rabbit thigh muscle were performed and results showed a general agreement between the two modalities ͑slope= 0.96 and R 2 = 0.67͒. The temporal information by the ultrasound measurement indicates that the parameters in MR ARF imaging should be optimized according to the tissue type, acoustic power, and envelope and frequency of the ARF modulation.
Diagnostic and high intensity focused ultrasound (HIFU) phased-arrays provide many advantages over single element transducers, including dynamic focal beam steering capability. These arrays should be fabricated with element-toelement pitch smaller than half the wavelength at the resonance frequency to avoid unwanted secondary foci due to grating lobes and side lobes. However, smaller pitch increases the electrical impedance of the array as the resonance frequency increases. The most common way to compensate the impedance increase is to employ electrical matching circuits between an array and RF driving system. However, it is not ideal if the number of array elements increases due to high fabrication cost and effort. In this paper we introduced the lateral mode coupling method to reduce electrical impedance in the fabrication of phased array. Using the lateral mode coupling method, we fabricated and tested onedimensional, linear diagnostic (750 kHz) and HIFU (1.4 MHz) phased-arrays. The averaged electrical impedances of each channel were measured to be 62.3 ± 5.2 Ω for the diagnostic array and 104.5 ± 8.9 Ω at zero phase for the HIFU array, respectively. The averaged maximum surface acoustic intensity of the HIFU array elements was 34 W/cm^2 prior to failure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.