Optimizing lesion contrast without using contrast agents

The essence of optimizing lesion detection is increasing the signal-to-noise (S/N) for the lesion while decreasing the S/N of the background. Maneuvers which improve one aspect of lesion detection may have a deleterious effect on another. For example, thinner slices decrease partial volume averaging (important for detection of small lesions) but also decrease S/N. Attempts to increase S/N by lowering the bandwidth may increase the TE, decreasing the degree of T1-weighting. Fast spin echo (FSE) generally offers the best T2-weighting for detection of long T2 lesions. However, lesions with short T2s (due to magnetic susceptibility effects) are better detected with gradient echo techniques. Strategies which decrease background S/N include those based on chemical shift differences (ie, spectroscopic techniques like FatSat) and those based on differences in T1 (ie, inversion recovery [IR] techniques like STIR and FLAIR).