Contrast and accuracy of relaxation time measurements in acquired and synthesized multislice magnetic resonance images

The effects of interslice spacing, the number of data points and other factors on the accuracy of relaxation time measurements and contrast have been investigated for both acquired and synthesized multislice MR images using experiments and computer simulations. The cross-excitation between adjacent slices in multislice imaging affects both contrast and derived relaxation times. Such measurements also are affected by the T₁ and T₂ of the materials imaged, the pulse sequence timing parameters, and the number of data points used to estimate the relaxation times. Errors in T₁ and T₂ may be severe, particularly for slice spacings less than 0.5 slice thickness and for long T₁ and T₂ materials. Consequently, the difference in signal intensities between two materials with different relaxation times also varies with slice spacing and between acquired and synthetic images, particularly for strongly T₁-weighted images.