Compression of ^99mTC methylene diphosphonate bone scan images using discrete cosine transformation

The objective of this study was to find the optimum value of threshold for compression of ^99mTc-methylene diphosphonate (MDP) bone scan images using discrete cosine transformation (DCT). DCT was applied to 51 ^99mTc-MDP bone scan images and then the image of logarithmic value of DCT coefficients was inspected to determine the threshold. After inspecting the number of images of DCT coefficients, we estimated the appropriate value of the threshold to be 10. After the application of threshold = 10, compressed image was reconstructed by applying the inverse DCT. Compression factor was calculated by dividing the nonzero element after thresholding to the nonzero element before thresholding DCT coefficients. Nuclear medicine physicians compared the compressed images with its input images and labeled them as acceptable or unacceptable. During comparison of input and compressed images, we considered points such as smoothening, blocking artifacts, body contour, gap between closely placed lesions, and detectability of lesion. Forty-four compressed images (out of 51 images) obtained at threshold 10 were acceptable to Nuclear Medicine Physician (NMP). Compressed images were less noisy compared to its input image. Compression factor was found to be 13.03 ± (minimum = 2.71, maximum = 42.92). The optimum value of threshold for compression of ^99mTc-MDP bone scan images was found to be 10, and the average compression factor achieved was equal to 13.03 (92.30%). (author)