Development of an algorithm to automatically compress a CT image to visually lossless threshold

• Published in: BMC medical imaging Vol. 18; no. 1; pp. 53 - 9
• Main Authors: Nam, Chang-Mo, Lee, Kyong Joon, Ko, Yousun, Kim, Kil Joong, Kim, Bohyoung, Lee, Kyoung Ho
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 17-12-2018; BioMed Central; BMC
• Subjects: Adult; Algorithms; CAT scans; Compression; Compression tests; Computed tomography; Computer applications; Computing time; Correlation analysis; Costs; CT compression; Data Compression - methods; Dependent variables; DICOM header; Digital imaging; Humans; Image coding; Image compression; Independent variables; Linear Models; Linear models (Statistics); Medical imaging; Noise; Performance evaluation; Radiographic Image Interpretation, Computer-Assisted - methods; Radiography, Abdominal - methods; Regression analysis; Regression models; Reproducibility of Results; Researchers; Signal-To-Noise Ratio; Statistical analysis; Technical Advance; Tomography; Tomography, X-Ray Computed; Training; Variables; Variance analysis; Visual signals; Visually lossless threshold; Wavelet transforms; DICOM header; CT compression; Visually lossless threshold
• ISSN: 1471-2342; 1471-2342
• DOI: 10.1186/s12880-017-0244-2

To develop an algorithm to predict the visually lossless thresholds (VLTs) of CT images solely using the original images by exploiting the image features and DICOM header information for JPEG2000 compression and to evaluate the algorithm in comparison with pre-existing image fidelity metrics.
Five radiologists independently determined the VLT for 206 body CT images for JPEG2000 compression using QUEST procedure. The images were divided into training (n = 103) and testing (n = 103) sets. Using the training set, a multiple linear regression (MLR) model was constructed regarding the image features and DICOM header information as independent variables and regarding the VLTs determined with median value of the radiologists' responses (VLT
) as dependent variable, after determining an optimal subset of independent variables by backward stepwise selection in a cross-validation scheme. The performance was evaluated on the testing set by measuring absolute differences and intra-class correlation (ICC) coefficient between the VLT
and the VLTs predicted by the model (VLT
). The performance of the model was also compared two metrics, peak signal-to-noise ratio (PSNR) and high-dynamic range visual difference predictor (HDRVDP). The time for computing VLTs between MLR model, PSNR, and HDRVDP were compared using the repeated ANOVA with a post-hoc analysis. P < 0.05 was considered to indicate a statistically significant difference.
The means of absolute differences with the VLT
were 0.58 (95% CI, 0.48, 0.67), 0.73 (0.61, 0.85), and 0.68 (0.58, 0.79), for the MLR model, PSNR, and HDRVDP, respectively, showing significant difference between them (p < 0.01). The ICC coefficients of MLR model, PSNR, and HDRVDP were 0.88 (95% CI, 0.81, 0.95), 0.85 (0.79, 0.91), and 0.84 (0.77, 0.91). The computing times for calculating VLT per image were 1.5 ± 0.1 s, 3.9 ± 0.3 s, and 68.2 ± 1.4 s, for MLR metric, PSNR, and HDRVDP, respectively.
The proposed MLR model directly predicting the VLT of a given CT image showed competitive performance to those of image fidelity metrics with less computational expenses. The model would be promising to be used for adaptive compression of CT images.