The project's long-term objective is to provide a capsule that will permit functional magnetic resonance imaging (fMRI) to be carried out on test animals conveniently without subjecting these animals to the stresses associated with the acoustic noise produced by MRI equipment. Such a capsule will facilitate imaging research on animal models to identify brain changes associated with the use and abuse of psychoactive substances, since acoustic noise stress interacts with the effects of these substances. A proof-of-principle capsule of a clear plastic will be built to accommodate a small primate and fit into a typical MRI system. Acoustical measurement equipment that can operate reliably in a MRI scanner's intense magnetic fields will be obtained and its performance will be verified. The intial capsule will be provided with various acoustic barrier arrangements consisting of double-wall structures and resilient layers topped by massive layers, with acoustically absorptive layers added on the exterior. The noise isolating performance of these barrier arrangements will be measured, modeled analytically, and optimized -- both for conventional scanning and for scanning protocols that generate acoustic noise in only limited frequency ranges. Detailed design of two prototype capsules with high acoustic attenuation will be carried out. The design will take account of non-acoustical requirements, such as the need to observe the test subject, the need to clean and disinfect the capsule, and accommodation of animals of slightly different sizes. An initial study aimed at enhancing the capsule's noise isolation performance by active control means will be performed. This study will address sensor and actuator locations and types, the transfer functions between these, and the control logic. ? ?
| Ungar, Eric E (2006) A note on the low-frequency noise reduction of cylindrical capsules (L). J Acoust Soc Am 120:3467-70 |
