Fractal analysis for the assessment of pulmonary blood flow on chest radiographs

The authors investigated whether fractal analysis can be used with chest radiography for assessment of increased pulmonary blood flow. As a physical measure they used a fractal dimension (FD), which can be used for quantifying texture in selected regions of interest (ROIs). In general, the pulmonary capillary wedge pressure (PCWP) is normally less than 10 mm Hg, the redistribution of pulmonary blood flow reflects PCWP greater than or equal to 10 mm Ha, and the interstitial edema is observed in PCWP greater than or equal to 20 mm Hg. So, the study group consisted of 34 patients with mitral stenosis and 46 patients without mitral stenosis. These patients with and without mitral stenosis were divided into three groups based on their pulmonary capillary wedge pressure (PCWP): normal (n = 38; PCWP, <10 mmHg), mildly increased (n = 26; PCWP, 10 to <20 mmHg), and severely increased (n = 16; PCWP, greater than or equal to20 mmHg). ROIs were selected in the right upper and lower lung zones of digitized chest radiographs, and FDs were calculated in each ROI As a measure of increased pulmonary blood flow, the upper-to-lower FD ratio (FDu/L) was calculated. Five chest radiologists estimated the degree of increased pulmonary blood flow for the same images of ROI sets presented on a cathode ray tube monitor in a randomized order. Between the normal PCWP group and the increased PCWP group, there were no significant differences in utility between the FDu/L and radiologists (P = 0.063). However, when the normal and the mildly increased PCWP groups were compared, the utility of the FDu/L was superior to that of radiologists (P = 0.042). These results indicate that fractal analysis is useful for quantitative estimation of increased pulmonary blood flow, especially in cases of mildly increased pulmonary blood flow.