DENSE and HARP: Two views on the same technique of phase-based strain imaging

Purpose: To discuss differences between displacement encoding with stimulated echoes (DENSE) and the harmonic phase (HARP) in imaging and reconstruction strategies. Materials and Methods: HARP and DENSE are presented in their historical context: while the HARP method was developed from the framework of myocardial tagging, DENSE arose from the framework of stimulated echo and displacement encoding using bipolar gradients. Both techniques have evolved since their introduction, thereby becoming more similar over time and losing their distinct features. Newly introduced improvements have successfully been applied in both methods. Differences between both methods are discussed point by point. Results: From this discussion it follows that almost all apparent differences are in fact nonexistent. Conclusion: In the literature, both techniques are still regarded as distinctly different techniques, where a more general treatment of the technique is justified. Once it is realized that both frameworks are easily merged, the benefits are 1) less confusion about the (dis)advantages of either technique, and 2) understanding of phase-based strain imaging that is more general than HARP or DENSE alone.