Objective and Subjective Evaluation of Compressed Computed Tomography (CT) Images

Techniques commonly employed for image data compression result in some degradation of the reconstructed images. Evaluation of the quality of medical image compression remains an important issue. In our study, we evaluated the diagnostic quality of the compressed Computed Tomography (CT) images using both objective and subjective tests. Three different CT images namely brain, chest, and abdomen were compressed and reconstructed by using Wavelet Compression Engine software (standard edition 2.5) for different compression ratios. Both objective and subjective methods were evaluated for 9 reconstructed images. Thirteen observers from Department of Radiology at the Sebha University carried out the subjective test. The Peak-Signal-to-Noise-Ratio (PSNR), which represents the quality of reconstructed images obtained, was between 57 to 36 dB and 52 to 34 dB for chest and abdomen images respectively, whereas for brain it was 57 to 40 dB. All these images were compressed until 30:1 compression ratio. By using subjective test, compression ratio of 30:1 is acceptable for diagnosis chest and abdomen images, and 20:1 for brain images