Optimization of imaging conditions in pediatric dynamic chest radiography: a virtual imaging trial
Ventilatory impairment is detected as decreased changes in lung density during respiration in dynamic chest radiography (DCR). The purpose of this study was to determine optimum imaging conditions in pediatric DCR through a virtual imaging trial (VIT). An XCAT phantom of a one-year-old infant with normal breathing and heart rate was generated. An air sphere was inserted into the lung to simulate a locally collapsed lung. The XCAT phantom was imaged at various combinations of imaging rate (6 or 15 frames/sec), tube voltage (50-100 kV), and mAs (0.08, 0.11, 0.16, 0.20 mAs/frame) using an X-ray simulator. The maximum changes in pixel value (Δpixel values) during respiration were measured on the projected air sphere and its surrounding normal regions to calculate the reduction rate of Ǐ"pixel values (Δpixel values%). On the requirements that the total entrance surface dose (ESD) is less than twice as that in conventional pediatric chest radiography, and that at least 4 sec imaging period is required to include 2 to 3 respiratory cycles for the assessment of pulmonary function, optimum imaging conditions were identified as those yielding a higher Δpixel values%. In the results, Ǐ"pixel values and Ǐ"pixel values% were found to increase with the increase in tube voltage and mAs/frame, indicating higher tube voltage and mAs are more advantageous for the detection of ventilatory impairments. On the other hand, the ESD metrics also indicated several conditions satisfying the requirements. We confirmed that the use in combination of Ǐ"pixel values% and ESD metrics allowed to reach recommended ones (e.g., 60 kV, 0.16 mAs/frame) for the evaluation of pulmonary function in pediatric DCR. The VIT was useful to identify optimum imaging conditions and image quality in pediatric DCR.
