Evaluations of magnetic resonance imaging parameters with simple phantoms

Imaging parameters associated with a clinical magnetic resonance imaging (MRI) system, evaluated with the use of simple and inexpensive phantoms, are described in evaluation of a clinical MRI system. Images, obtained with a Diasonics 0.35-T MRI system using an elliptical whole-body radio frequency coil, are presented which demonstrate geometric distortion, inaccuracy of image dimensions, and artifacts. Measurements of reproducibility and uniformity of both signal intensity and spin-lattice relaxation times are presented for uniform phantoms. Replicate measurements are analyzed by two-way analyses of variance to determine the significance of variations as a function of position and slice. Apparent T1's are not significantly different among the slices for the images analyzed, but there is a significant effect due to position in the field. Direct measurement of the radio frequency field for the center slice follows a pattern which is similar. Spin-lattice relaxation times are compared among two-point calculations and nonlinear four-point calculations, and the effects of pooling data are found to increase the precision of T1 measurements.