Variations in slice shape and absorption as artifacts in the determination of tissue parameters in NMR imaging.

Existing models for the contrast between one tissue and another in NMR imaging have shown that there are regions of ambiguity particularly in spin-echo sequences. This paper indicates that there are further problems due to variations in slice formation with tissue parameters, and that it is necessary to be very conservative in assessing the magnitude of T1 in any imaging system. The change in shape affects the appearance of images due, in essence, to adjustments in partial volume effects, with some of the contributions to the signal from lesions with long T1 coming from different regions to those for normal tissue. A simple model for a slice is used because the actual form in a real imaging situation is the result of a number of factors which are usually not accurately enough known.