Measuring Practical Coil Array Performance with Respect to Ultimate Intrinsic SNR: A Tool for Array Design and Assessment

R. Lattanzi, A. K. Grant, M. A. Ohliger, D. K. Sodickson Division of Health Science and Technology, Harvard-MIT, Cambridge, MA, United States, Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States Introduction As the number of available receiver channels on modern MR systems increases, increasing attention will be paid to the design and performance of many-element RF coil arrays. Questions regarding the balance of coil-noise and sample-noise or the suitability of any particular array design for parallel imaging– already areas of great practical interest to coil designers – promise to take on new significance as the number of elements increases. In this context, it would be useful to have a concrete metric of coil performance, in order not only to compare different designs but also to determine how much room for improvement there may be in any particular design. Recent studies have shown that there is an inherent electrodynamic limitation to the achievable SNR for any physically realizable coil array (assuming sampledominated noise), and have modeled the behavior of ultimate intrinsic SNR either in the absence [1] or in the presence [2,3] of parallel acceleration. In [1], coil performance maps were also presented, in which the actual SNR of particular coils was compared with the appropriately scaled ultimate intrinsic SNR for a particular phantom and image plane geometry. In this work, we extend the computation of coil performance maps to include the effects of parallel imaging. We compute the ultimate SNR at each point within a central cross-section of a cylindrical phantom for a variety of acceleration factors, and express the actual SNR, measured with a particular eight-element coil array in a phantom with the same geometry, as a percentage of the ultimate achievable value. Such coil performance maps may of course be generated for arbitrary coil arrays and object/image geometries, and they may ultimately be used as absolute references for coil design optimization.