Precision of magnetic resonance velocity and acceleration measurements: Theoretical issues and phantom experiments

Magnetic resonance (MR) sequences have been developed for acquiring multiple components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precision of measurements: N-S, the number of flow-encoding steps; NEX, the number of signal accumulations; and N-D, the number of dimensions. Our aims were to establish a general relationship revealing the precision of these measurements as a function of N-S, N-D, and NEX and to validate it by experiments using phantoms. Previous work on precision has been restricted to two-step (N-S = 2) or ID (N-D = 1) MR velocity measurements. We describe a comprehensive approach that encompasses both multistep and multidimensional strategies. Our theoretical formula gives the precision of velocity and acceleration measurements. It was validated experimentally with measurements on a rotating disk phantom. This phantom was much easier to handle than fluid-based phantoms. It could be used to assess both velocity and acceleration sequences and provided accurate and precise assessments over a wide, adjustable range of values within a single experiment. Increasing each of the three parameters, N-S, N-D, and NEX, improves the precision but makes the acquisition time longer. However, if only one parameter Is to be assessed, maximizing the number of steps (N-S) is the most efficient way of Improving the precision of measurements; several parameters are of interest, they should be measured simultaneously. By contrast, increasing the number of signals accumulated (NEX) is the least efficient strategy. (C) 2001 Wiley-Liss, Inc.