Anders Tingberg

Purpose: To investigate the relative importance of spatial resolution and noise on the image quality of clinical radiographs. Methods: The spatial resolution and noise of fifteen digitised lumbar spine radiographs were altered with image processing. Three different MTF curves and three different Wiener spectra were combined into seven different combinations of spatial resolution and noise. These seven combinations were applied to the original data set, and the resulting images were printed on film. Seven expert radiologists evaluated the clinical image quality of the resulting images with visual grading analysis (VGA) of structures based on the European Image Criteria. Results: The results show that added noise is more deteriorating than reduced spatial resolution for the clinical image quality. For a given MTF and noise level, the worst was the one with increased noise followed by the one with both reduced MTF and added noise (mimicking a faster screen-film combination). Reduced MTF only gave the highest rating. Conclusions: It is more important to find methods for removing noise than to try to improve the MTF of a radiographic system. A noisy image can sometimes be improved by reducing the spatial resolution.