**4. Conclusions**

In this paper, we propose a novel dictionary-based image reconstruction algorithm in which the desired information of the images is shown more accurately. The proposed method uses a combination of WT, DCT, and TV in order to preserve the necessary information within the reconstruction procedure. The algorithm was evaluated experimentally (using a single-element PACT system). EPI and PSNR were used as the quantitative metrics of evaluation. The qualitative and quantitative results presented here show that the proposed algorithm can generate images with specific emphasis on a desired feature, defined by the user. Quantitative analysis of EPI showed that, for a number of angles lower than 45, the proposed algorithm preserves the edges better than other methods. In addition, the calculated PSNR at 60 angles indicated that the proposed method improves PSNR by about 27%, 9%, and 7%, compared with BP, WT, and WT+TV, respectively. At every view angle, the improvement obtained by the proposed method compared to the above-mentioned methods was statistically significant (*p*-value < 0.001). The proposed technique is particularly useful when a low-cost PACT system (limited number of view angles) with a fine temporal resolution is required. However, all the improvements are obtained at the expense of a higher computational burden. As a feature work, we will evaluate the proposed method in an in vivo study. Accelerating the algorithm as well as reducing its computational complexity is the next major step.

**Author Contributions:** Conceptualization, P.O. and M.M.; Methodology, P.O., M.M. and A.H.; Software, P.O., A.H., M.Z., M.M. and X.H.; Validation, P.O., M.M., A.H., M.Z. and X.H.; Formal Analysis, P.O., A.H., M.M., X.H.; Investigation, P.O., M.M.; Resources, P.O., M.M., A.H., M.Z. and X.H.; Data Curation, P.O., A.H. M.Z. and X.H.; Writing—Original Draft Preparation, P.O., M.M., A.H., M.Z. and X.H.; Writing—Review & Editing, P.O., M.M., M.N., M.O.; Visualization, M.N. and M.O.; Supervision, M.N. and M.O.; Project Administration, M.N.; Funding Acquisition, M.N.

**Funding:** This project has been partially supported by a WSU startup fund and the Andersen Institute fund.

**Acknowledgments:** We thank Jun Xia from Buffalo University for his constructive discussion and help in image reconstruction.

**Conflicts of Interest:** The authors declare no conflict of interest.
