# An Integrated Dictionary-Learning Entropy-Based Medical Image Fusion Framework
## 4 Experiments and Analysis
### Image Quality Comparison
#### 4.2.3 MRI-SPECT Image Fusion Comparative Experiments  
The 'brain' images are a pair of MRI and SPECT images shown in Figure 8a,b respectively. Similarly, the MRI image also shows the image of brain slices with soft-tissue information in this experiment. The SPECT image provides the true 3D information of brain slices that is typically presented as cross-sectional slices through the patient, and can be freely reformatted or manipulated as required. BSD, DWT, DT-CWT, CS-DCT, KSVD-OMP, MFR, SRDL, JPC, MST-SR, and the proposed IDLE are employed to merge MR and SPECT images into 3D image with soft-tissue information. The corresponding fusion results are shown in Figure 8c-l respectively.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **AG** & **EI** & \(\mathbf{Q^{AB/F}}\) & **MI** & **VIF** \\ \hline BSD & 6.7133 & 69.2493 & 0.3069 & 1.8505 & 0.2611 \\ DWT & **6.8695** & **70.8721** & 0.3128 & 1.7715 & 0.2447 \\ DT-CWT & 4.9488 & 47.1991 & 0.3147 & 1.8667 & 0.2954 \\ CS-DCT & 4.1109 & 42.9211 & 0.2955 & 1.8330 & 0.2694 \\ KSVD-OMP & 3.5764 & 36.7095 & 0.2840 & 1.7970 & 0.2842 \\ MFR & 4.9026 & 47.9372 & 0.3155 & 1.8673 & 0.3096 \\ SRDL & 5.0374 & 49.1628 & 0.3163 & 1.8571 & 0.3142 \\ JPC & 4.6936 & 47.6084 & 0.3184 & 1.8647 & 0.3086 \\ MST-SR & 3.7241 & 38.9104 & 0.2894 & 1.8163 & 0.2907 \\ Proposed IDLE & 4.7137 & 48.0413 & **0.3199** & **1.8744** & **0.3161** \\ \hline \hline \end{tabular}  
* The highest result of each objective metric is marked in bold-face.  
\end{table}
Table 2: Objective Evaluations of MRI-PET Image Fusion Comparative Experiments.  
Figure 8: MRI-SPECT Image Fusion Comparative Experiments, (**a**) is the MRI source image; (**b**) is the SPECT 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.  
The fused image (c) obtained by BSD has serious block effects that make the details unclear. The DWT result has a chromatic dispersion that may cause medical misdiagnosis. The fused image of DT-CWT has good performance in contrast, sharpness and details. CS-DCT does not generate the high-quality fused image. The details of the fused image are blurred and contain lots of noises. Although the overall contrast of KSVD-OMP fused image is good, parts of details are blurred and the sharpness is not good. MFR, SRDL, and JPC generate high-quality fused image respectively. The further comparisons are shown in following objective evaluations. As for the previous two experiments, the fused image of MST-SR is still brighter than the source image. The details of the fused image using the proposed solution has high contrast, sharpness, and brightness.  
Table 3 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. BSD gets the largest value in AG and EI, but the block effect seriously affects the quality of fused image. According to the objective evaluations, the proposed IDLE has the best overall performance in MR and SPECT image fusion among all 10 methods.