Quantitative analysis of resolving power for computed radiographic portal images

This study presents a quantitative analysis method of resolution for computed radiography (CR) portal images using three different types of cassettes. A copper wire chart (test piece, Shimadzu Medical Corp.) for fluoroscopy was selected as the test tool for analysis. Images of the test chart were obtained on a linear accelerator operating at nominal beam energies of 4 MV. The CR portal imaging data were transmitted to a personal computer via a DICOM network system. The imaging data were imported into NIH Image, which is public domain software. The extent of analysis was established on the chart image (160 x 540 pixels). A density profile plot was generated based on the current rectangular selection and this plot was used was used for quantitative analysis of the resolution. This quantitative analysis method using NIH Image is expected to prove useful for digital portal images.