CT I

Abstract

The equation that governs the image intensity in projection imaging is: () ∫ − = dz z y x I y x I d) , , (exp) , (0 µ Projection x-ray systems are the most inexpensive and widespread medical imaging device, but there are some major drawbacks: • There is no depth (z) information in the images – we can't tell where along a particular line where a lesion is located. • Lack of contrast – large changes in attenuation coefficient may results in very small changes in image intensity. We define contrast as the change in intensity relative to the background intensity: e.g. we can define a contrast S S C / ∆ = and a contrast to noise ratio s S CNR σ / ∆ = . High contrast in the attenuation coefficient might yield low contrast in the projection image.