Image-guided therapy of a tissue can utilize magnetic resonance imaging or another medical imaging device to guide an instrument within the tissue. A control circuit compares a feedback voltage, which is in accordance with the output voltage, and a reference voltage and controls the switch circuit in response to a switching timing that is in accordance with the comparison result. A flexural spring arrangement is mounted on the support plate with a fixed inner end and extends radially outwardly to an inertial mass. Source and receiver apertures may then be determined by ray tracing. More specifically, this application communicates our discovery of pharmaceutical compositions and methods of use in the prevention and treatment of HIV infection. The disclosed invention provides for modular placement and support for different types of microphones within a percussion instrument, as well as improved microphone isolation for better sound quality in a sound studio or recording environment.