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

Magnetic resonance (MR) sequences have been developed for acquiring multipl e components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precisio n 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 t o establish a general relationship revealing the precision of these measure ments 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 comprehen sive approach that encompasses both multistep and multidimensional strategi es. Our theoretical formula gives the precision of velocity and acceleratio n measurements. It was validated experimentally with measurements on a rota ting disk phantom. This phantom was much easier to handle than fluid-based phantoms. It could be used to assess both velocity and acceleration sequenc es and provided accurate and precise assessments over a wide, adjustable ra nge of values within a single experiment. Increasing each of the three para meters, 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 precis ion of measurements; several parameters are of interest, they should be mea sured simultaneously. By contrast, increasing the number of signals accumul ated (NEX) is the least efficient strategy. (C) 2001 Wiley-Liss, Inc.