Reproducibility of relaxation and spin-density parameters in phantoms and the human brain measured by MR imaging at 1.5T

Abstract
The reproducibility of T1, T2, and proton density, measured in phantoms and the human brain was evaluted by proton imaging techniques. The sequence used to derive T1 and density values was a multiple‐saturation recovery which consists of four pairs of 90° pules, followed by a 180° phase reversal pulse, generting four T2‐weighted images. The data were analyzed by fitting the pixel intensities to the respective equations by means of nonlinear multi‐parameter least‐squares analysis. Short‐term reproductibility between four consecutive scans was evaluted to b 1–40% depending on location with a covering the entire span of physiological T1 and T2 values. A second phantom containing a series of identiical samples served to study the depeendence of the apparment T1 and T2 on position, both radially and axially, with respect to magnet isocneter. Reproducibility across the field of view was found to be better than 7% (T1 and T2). This phantom was further used to evaluate effects of long‐term reproductibility, which at each location varied from 5–14% (T1) and 2–10% (T2). Finally, interinstrument reprducibilty, tested by means of the same protcol on three different insturments, all operating at the same magnetic field and using largely indentical hardware for each location, was found to be 1–14% (T1) and 2–10% (T2). The positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity. Finally, brain tissue relaxation and spin‐density data were determined using the same protocol in 37 scans performed on 27 normal volunteers. The tissues analyzed were putamen, thalamus, caudate nucleus, centrum semiovale, internal capsule, and corpus callosum. Excellent accordance was further obtained between left and right hemispheres. © 1986 Academic Press, Inc.