One of the potentials of Digital Radiography has been for quantitative measurement, both spatial or contrast. This potential has been realized for contrast in computerized tomography. All projection radiography is somewhat limited in quantitative density analysis by line of sight integration. However, by comparing two successive images of the same subject, differences between them may be assessed. If that difference is due to contrast material which fills an organ, then the image differences can be used to infer geometric organ information. To be successful the imaging system must be of sufficiently low noise, have low external and internal scatter, and have a well known X-ray energy to digital signal transfer function. If these conditions are met, the signal differences may be calibrated absolutely. AS&E's flying spot digital radiographic system has been used to implement two examples of this technique. They are the determination of lung line of sight depth using Xenon as a contrast material and determination of cardiac chamber dimensions by using the cyclic variations in line of sight blood depth.
|