Fundamental information content accessible with medical x-ray scatter imaging

Although scattered radiation is generally regarded as a nuisance in radiological imaging, many innovative imaging concepts that use the scattered field have been demonstrated. A systematic approach, however, for analyzing the medical applications of x-ray scatter imaging has been lacking. We have therefore formulated a simple semi-analytic model that consists of imaging a target object against a background material of the same dimensions when both are situated within a water phantom. The target and background objects have small cross-sectional areas (1.0 mm(2)) to allow the omission of self-attenuation and multiple scatter within the objects. The incident energy fluence is kept constant so that similar doses are delivered by the various photon beams. For imaging white brain matter versus gray brain matter in a 15 cm thick water phantom, the maximum signal-to-noise ratio, over all photon energies, for images obtained with the forward scatter between 2 degrees - 12 degrees exceeds that of primary images for all object thicknesses less than or equal to 40 mm. The penalty in dose as a result of spectral blur is generally moderate. For example, using an 80 kV beam for the previous imaging task would require approximately a 24% dose increase relative to using a monoenergetic beam. A high-precision experimental apparatus has been assembled to validate our predictions.