EQUALIZATION TECHNIQUES IN CHEST RADIOGRAPHY

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Chest radiography is the most important diagnostic examination for the detection of asymptomatic lung disorders including cancer and plays a central role in the monitoring of other major cardiopulmonary diseases such as heart disease and pneumonia. Conventional chest radiography is technically difficult due to the large variations in tissue thickness between the lung zones (15 cm) and the mediastinal, diaphragmatic and cardiac portions (30 cm) which can result in 50 fold variations in film exposure. Considering the approximately 10 fold useful exposure range of radiographic film. This condition results in chest radiographs where soft tissue contrast over the thicker body parts is compromised when the lung zones are rendered with maximum film contrast. We have developed an automatic technique of maintaining uniform film contrast over all parts of a chest radiograph by Scanning Equalization Radiography (SER) that regionally tailors the incident patient exposure so the large excursion in film density are eliminated. The technique uses conventional radiographic film and completes an image forming scan in 4.7 seconds. We have demonstrated the technical feasibility of this technique and a clinical study has shown that the exposure consistency characteristic of this technique results improved visualization of normal anatomy and greater diagnostic efficacy. We propose further development of this technique focusing on reducing our current scan time to minimize motion unsharpness, exploring the use of simultaneous energy and intensity equalization to enhance lung tissue subject contrast and testing the feasibility of more efficient methods of SER using multiple scanning beams.