MTF measurements of clinical image protocols

DR images differ significantly in appearance from traditional screen film radiographs, largely due to the sophisticated image processing algorithms applied at the ‘For Processing’ stage. However the IEC protocol (IEC, 2003) [1] for measuring the pre-sampled MTF of DR systems is based on the ‘For-processing’ version of the final image, which tests only the hardware. Crucially any software effects on image quality are ignored. MTF Curves were calculated on a range of ‘For Presentation’ images and were compared with the corresponding IEC mandated MTF curves from ‘For Processing’ images. ‘For Presentation’ MTF curves differ not only between clinical protocols, but also between manufacturers. In each case the high frequency response was greater in ‘For-Presentation’ images, indicating the effectiveness of the image processing algorithms. The absence of any guidance or standards on appropriate levels of image processing for clinical protocols is noted. This is necessary as the image processing applied significantly affects the system response and, therefore, the appearance of the ‘For Presentation’ images reported by radiologists. Further investigation is merited, perhaps at the European level. A new set of standards should be considered, which take into account the software effects on image quality; these could be investigated as part of a revised RP 162.