Histogram-directed processing of digital chest images

One of the potential advantages of digital chest imaging is the ability to process these images. However, such processing, when uniformly applied to the entire image, is often unsatisfactory due to the different processing requirements of lung field and mediastinum. Therefore, a method to selectively process these regions based upon the histogram of the original image has been developed. Thirteen conventional chest films were digitized with a laser film scanner. Analysis of individual lung field and mediastinum histograms showed that the chest image histogram is essentially bimodal with significant lung field-mediastinum histogram peak separation; overlap between these peaks is small (9% of the total histogram) and insensitive to minor pathologic change or radiographic technique. Using these histograms, a gray level threshold distinguishing mediastinum from lung field was selected and used to direct the regionally-selective processing of several chest images. This technique may prove especially useful for digital enhancement of the underexposed mediastinum often encountered on conventional chest radiographs.