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

作者：Li Baojun^*; Behrman Richard H; Norbash Alexander M

来源：Medical Physics, 2012, 39(6): 3456-3465.

DOI：10.1118/1.4718569

• computed tomography
• dose
• patient size index
• topogram
• attenuation area product
• miscentering

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 mu a values, where mu is the normalized tissue attenuation coefficient and a is the area per pixel. Four topogram-based body size indices [average diameter ((D) over bar), 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) over bar 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 (E'(topo)) 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) over bar 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) over bar (+/-2.1 cm, p < 0.01). The standard error for estimation of D-w from (E'(topo)) was +/-1.3 cm, significantly less than that from E-topo (p < 0.01).
Conclusions: Among the four topogram-based patient body indices, (E'(topo)) is the most accurate for estimation of individual x-ray attenuation of the scanned body region. Thus, (E'(topo)) is an optimal topogram-based patient body size index that is relevant for determining the proper CT dose level for individual patients.

• 出版日期2012-6