Comparison of topogram-based body size indices for CT dose consideration and scan protocol optimization

摘要

Purpose: To retrospectively compare different topogram-based patient body size indices and to determine the optimal topogram-based body size index as a basis for body computed tomography (CT) dose consideration and scan protocol optimization. Methods: Forty-three routine thorax and abdomen CT scans are studied retrospectively, with patient ages ranging from 18 to 67 yr. The individual patient's water-equivalent diameter (D w) of the scanned body region is computed from CT DICOM images as the gold standard, after first converting from Hounsfield units values to μa values, where μ is the normalized tissue attenuation coefficient and a is the area per pixel. Four topogram-based body size indices average diameter (D ), girth (G), topogram projection area (E topo), and improved topogram projection area (E topo ') are computed and correlated with D w using linear regression analysis. Specifically, D is calculated by averaging the coronal and sagittal diameters; G is computed by modeling the patient's cross-section as an ellipse; E topo is the product of the mean topogram pixel value and the width of the scanned body region; and (Etopo') incorporates E topo with correction of patient miscentering and water attenuation coefficient. The accuracy of these four approaches for estimation of D w is assessed using linear regression models. Results are given in terms of 95 confidence intervals (CIs). Results: Regression analysis results in four different linear models. The standard error (95 CI) for estimation of D w from D and G was ±2.8 and ±3.1 cm, respectively (p 0.297). The standard error for estimation of D w from E topo was significantly less than that from D (±2.1 cm, p 0.01). The standard error for estimation of D w from (Etopo') was ±1.3 cm, significantly less than that from E topo (p 0.01). Conclusions: Among the four topogram-based patient body indices, (Etopo') is the most accurate for estimation of individual x-ray attenuation of the scanned body region. Thus, (Etopo') is an optimal topogram-based patient body size index that is relevant for determining the proper CT dose level for individual patients.