Abstract
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 flowโencoding 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 twoโstep (N~S~ = 2) or 1D (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 fluidโbased 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; if several parameters are of interest, they should be measured simultaneously. By contrast, increasing the number of signals accumulated (NEX) is the least efficient strategy. J. Magn. Reson. Imaging 2001;13:445โ451. ยฉ 2001 WileyโLiss, Inc.