Purpose: To use the patient height and weight, which are accessible from most Radiology Information Systems, to create a radiographic technique chart for portable chest images. By providing technologists with size-based imaging techniques, it is expected that diagnostic quality images may be captured for a variety of patient sizes without exposing the patient to excess radiation.
Methods: Technique charts for portable chest images were derived from image data, over a period of three months (170 exposures). Patients were modeled as water-equivalent cylinders, having a diameter determined from their weight and assumed density of 1.00g/cm3, and length equal to their height. Technique charts were created through a two-step process: first calculating soft-tissue attenuation coefficients for x-ray spectra ranging from 50-120kVp using SPEKTR spectrum generating code, then estimating the patients' tissue-equivalent attenuation thickness based off the image technique. The kVp and mAs were then chosen to achieve the desired detector exposure for a range of patient heights and weights.
Results: The relationship between the patients’ tissue-equivalent attenuation thickness and the square root of their weight over height was linear, having a slope of 0.63±0.03, intercept of 0.59±0.51cm and R² of 0.701. The technique chart greatly improved the variability in EI values, reducing the range from 360±200 to 300±80. The target EI for this technique chart was 300. Further, 90% of images (64 of 71) captured after implementing the technique chart had a DI between -2 and +2. The variability in EI values was significantly less in the proposed technique chart (p<0.001) than the standard technique chart.
Conclusion: Constructing a size-specific technique chart proved useful in maintaining a consistent image quality, as defined by the EI over a wide range of patient sizes. A size-based technique chart will guide technologists in adapting standard techniques to accommodate a wide range of patient sizes.