# An Integrated Dictionary-Learning Entropy-Based Medical Image Fusion Framework
## 4 Experiments and Analysis
### Image Quality Comparison
#### 4.2.2 MRI-PET Image Fusion Comparative Experiments  
The 'brain' images are a pair of MRI and PET images shown in Figure 7a,b respectively. The MRI image shows the image of brain slices that contain clear information of soft tissues. The PET image also shows the image of brain slices that produces a 3D image of functional processes in human body. BSD, DWT, DT-CWT, CS, KSVD-OMP, MFR, SRDL, JPC, MST-SR, and the proposed IDLE are employed to merge MRI and PET images into a clear image with soft tissues and functional processes information. The corresponding fusion results are shown in Figure 7c-l respectively.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **AG** & **EI** & \(\mathbf{Q^{AB/F}}\) & **MI** & **VIF** \\ \hline BSD & **7.1738** & **76.9148** & 0.6595 & 2.1021 & 0.4021 \\ DWT & 6.1569 & 56.8719 & 0.6284 & 1.3327 & 0.2952 \\ DT-CWT & 4.2628 & 46.2560 & 0.5097 & 1.2463 & 0.2632 \\ CS-DCT & 3.5918 & 38.7132 & 0.5063 & 2.0268 & 0.3046 \\ KSVD-OMP & 4.2109 & 46.0699 & 0.7762 & 2.5085 & 0.3493 \\ MFR & 6.0671 & 62.1495 & 0.7442 & 2.7284 & 0.3691 \\ SRDL & 4.6062 & 53.2307 & 0.7238 & 2.6084 & 0.3417 \\ JPC & 6.1482 & 64.5306 & 0.7264 & 2.5146 & 0.3908 \\ MST-SR & 4.4807 & 49.1622 & 0.6843 & 2.4708 & 0.3261 \\ Proposed IDLE & 6.1330 & 65.6209 & **0.8428** & **3.0158** & **0.4097** \\ \hline \hline \end{tabular}  
* The highest result of each objective metric is marked in bold-face.  
\end{table}
Table 1: Objective Evaluations of CT-MRI Image Fusion Comparative Experiments.  
Figure 6: CT-MRI Image Fusion Comparative Experiments, (**a**) is the CT source image; (**b**) is the MRI source image; and (**c**)-(**l**) are the fused images of BSD, DWT, DT-CWT, CS-DCT, KSVD-OMP, MFR, SRDL, JPC, MST-SR, and the proposed IDLE respectively.  
Similar to SPECT, the results of BSD and DWT have the issue of chromatic dispersion, and this may cause misdiagnosis. So BSD and DWT are not recommended to fuse MRI and PET images. The fused images of DT-CWT and KSVD-OMP have high quality, and both contrast and sharpness are also good. However, the detailed parts of these fused images have low brightness, compared with the proposed IDLE. MFR, SRDL, and JPC show a good performance in fusing source images. The fused image (k) of MST-SR is brighter than the source image. The fused image (l) of proposed IDLE has high quality in details, contrast, sharpness, and brightness.  
Table 2 shows the objective evaluations. Compared with the rest of the image fusion methods, the proposed IDLE gets the largest value in \(Q^{AB/F}\), MI, and VIF. DWT gets the largest value in AG and EI, but it has chromatic dispersion issues in fused images. So the proposed IDLE has the best overall performance in PET and MRI image fusion among all 10 methods, according to the quality of fused image, contrast, sharpness, brightness, and objective evaluations.  
Figure 7: MRI-PET Image Fusion Comparative Experiments, (**a**) is the MRI source image; (**b**) is the PET source image; and (**c**)–(**l**) are the fused images of BSD, DWT, DT-CWT, CS-DCT, KSVD-OMP, MFR, SRDL, JPC, MST-SR, and the proposed IDLE respectively.