Quantitative Spatial Analysis on Radiographic Features of Rotator Cuff Calcifications: An Exploratory Study

<b>Background/Objectives</b>: Plain radiography is the primary diagnostic tool for calcific tendinitis of the shoulder. Several qualitative grading methods have been proposed to represent the pathophysiologic phase and guide treatment decisions. However, these methods have demonstrated low reliability, complicating their effectiveness for such purposes. This study aims to perform the first quantitative analysis of calcific lesions using radiographic imaging and explore their correlation with ultrasonographic parameters to enhance their diagnostic utility. <b>Methods</b>: A total of 57 shoulders presenting with painful calcific tendinitis in either the supraspinatus or subscapularis tendon were reviewed. The calcific deposits and tendon regions of interest were meticulously identified and annotated. Image brightness was reduced to 256 grayscale levels, and descriptive and heterogeneity parameters, including skewness, kurtosis, complexity, and entropy, were quantified and analyzed. <b>Results</b>: In the region of calcification, the average grayscale values were 21.69 units higher than those of tendon tissue. All spatial heterogeneity parameters, except for skewness, demonstrated statistically significant differences when compared with the adjacent tendon. Notably, entropy and complexity were the most distinctive features, with an area under the curve of 0.93 and cut-off values of 4.62 and 4.18, respectively. Significant correlations were observed between the heterogeneity parameters and ultrasonographic findings, such as bursal contact and peri-calcific hypoattenuation. <b>Conclusions</b>: Calcific deposits demonstrated not only increased brightness in grayscale levels but also distinct spatial heterogeneity. The correlation with ultrasonographic findings indicates that these heterogeneity parameters may reflect underlying pathophysiological characteristics. Future prospective research could explore the whole temporal changes of calcifications more thoroughly.