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12 March 2009 The impact of focal spot size on clinical images
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The physical assessment of the spatial resolution produced by broad and fine focal spot sizes has been well established. There is however an evident lack of study into the impact of focal spot selection on clinical image quality. While the excessive use of the fine focus has an impact on tube life, the benefit of its use in radiological imaging should be investigated. Cadaver images were produced in order to compare the 0.8mm and 1.8mm focal spot sizes. The range of radiographic projections assessed included the medio-lateral ankle, antero-posterior (AP) knee, AP thoracic spine and horizontal beam lateral (HBL) lumbar spine. Five clinicians analysed the images using a 1 - 4 visual grading analysis score against a reference image to assess the visibility of specific anatomical criteria. A Mann- Whitney U statistical test was employed to assess the results. No significant statistical differences between the scores for the broad and fine focus images were found, although a non-significant higher score in image quality was shown for the fine compared with the broad focus images with large object to detector distance. No difference in image quality was shown for examinations traditionally produced with a fine focus. The study results questions the wide spread usage of fine foci for specific examinations, particularly for extremity examinations. Current practice based on international guidelines can lead to a reduced life and increased cost with little clinical benefit.
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Sinead M. Gorham and Patrick C. Brennan "The impact of focal spot size on clinical images", Proc. SPIE 7263, Medical Imaging 2009: Image Perception, Observer Performance, and Technology Assessment, 726312 (12 March 2009);

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