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Is Average Body Diameter Helpful in Choosing Exposure Technique in PA Chest X-Ray?

H Ai1*, (1) Rush University Medical Center, Chicago, IL


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: In 2019, 57% of all Chest X-ray exams performed at our institutions are performed on portable X-ray units. The purpose of this study is to assess the efficacy of using average body diameter in determining the appropriate mAs value for given kV.

Methods: Information of all clinical PA chest X-ray exposures from an AGFA DX-D600 stationary digital radiography unit in 2019 were exported via Radimetrics Enterprise Platform. Exposures meeting the following criteria were selected for analysis: 1) Deviation index is between -1 and 1 (target exposure index = 250); 2) Source to Image distance is within 2.5 cm of 180 cm; 3) kV = 120; 4) Patient age is at least 18, with both height and weight information available. A total of 200 PA chest exposures from 200 different patients were selected (Male = 78, Female = 122).
Using the model of a cylinder and assuming patient density is 1g/cm3, the average body diameter of each patient is estimated using formula
T = 2*sqrt(Weight/?/Height/p)
Linear regression analysis was performed between average body diameter and log10(mAs), as well as between body mass index (BMI, Weight/Height2) and log10(mAs) for all exposures.

Results: Average body diameter has a slightly higher correlation with log10(mAs) than BMI (R2: 0.603 vs 0.512, RMSE: 0.114 vs 0.127). The correlation of average body diameter with log10(mAs) is notably higher in female patients than in male patients (R2: 0.706 vs 0.459, RMSE: 0.102 vs 0.117), possibly because of more consistent body composition.

Conclusion: In exams with appropriate exposure levels, average body diameter has stronger correlation with log10(mAs) than BMI, especially in female patients. However, the overall weak correlation indicates that additional information is likely needed when considering exposure settings in clinical practice.

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