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.