Radiographic
system and method for noninvasively assessing the response of tissue to a compound, such as a therapeutic compound. In one embodiment, a non-radioactive, radio-opaque
imaging agent accumulates in tissue in proportion to the tissue concentration of a predefined cellular target. The
imaging agent is administered to a live
organism, and after an accumulation interval, radiographic images are acquired. The tissue being examined is transilluminated by X-
ray beams with preselected different mean energy spectra, and a separate radiographic image is acquired during
transillumination by each beam. An
image processing system performs a weighted combination of the acquired images to produce a first image. The
image processing procedure isolates the radiographic density contributed solely by differential tissue accumulation of the
imaging agent. A compound is administered to the
organism, and after a selected interval, a second radiographic image of the tissue is acquired. Radiographic density contributed by accumulated imaging agent in corresponding areas of tissue in the first and second images are compared. Differences in radiographic density between the images reflect changes in the concentration of the cellular target that have occurred after administration of the compound. The
system and method may be used to assess therapeutic
efficacy of compounds in the
drug discovery process, in clinical trials, and in the evaluation of
clinical treatment. In other embodiments, pharmacological and toxicological effects of a wide variety of compounds on tissue may be noninvasively assessed.