Recently, a variety of medical imaging systems have been introduced involving selective imaging using multiple measurements. In these systems a number of independent measurements, taken at different times and/or using different X-ray energies, are combined to form a selective image. A prime example is the selective imaging of iodine for vessel imaging. These systems, involving subtraction operations, result in a degradation of the SNR, as compared to the individual measurements. In this approach called measurement-dependent filtering, the low spatial frequencies are derived from the selective image and the high frequencies from a nonselective combination of the measurements which has a greater SNR. The combination provides a significantly improved SNR with the original resolution and a degree of "conspicuity" essentially equal to selective image.

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