Image Fusion is the process of integrating two or more images from a single modality or multiple modalities. A tumour can be formed either by uncontrolled growth of cells in a particular human organ or due to lesions caused by protracted radiation exposure. The objective of this paper is to implement an innovative image fusion system for the detection of brain tumours. Fusing images obtained from MRI and PET can accurately access the tumour response. In this work, the proposed image fusion technique consists of two major processes such as (I) image enhancement and (II) image fusion both depend on Discrete Wavelet Transform (DWT). Lagrange’s interpolation is used for image enhancement. MRI and PET images are fused based on image enhancement and fusion technique that has been implemented and simulated in MATLAB. The fused image has complement information from both MRI and PET images and the visual quality has improved. The fusion parameters Average Gradient, Discrepancy, PSNR, MSE and Entropy are calculated and the results show the effectiveness of fusion based on DWT. This work can be extended to diagnose any type of abnormalities in all human organs.