By studying this chapter, the reader should be able to:  Explain the origin of the f factor, and determine the dose (Gy) to a medium from knowledge of the exposure (C/kg).  Describe the attenuation of x rays in different tissues as a function of x-ray energy.  Discuss the properties of various tissues that permit their distinction in x-ray images.  Define changes in radiation dose at the interface between bone and soft tissue.  Identify the applications of high-voltage and low-voltage radiography.  Characterize the properties and applications of contrast media