Figure 2: Spectrum of imaging technologies. The currently available imaging technologies, to varying degrees, are used to image anatomy, physiology, or molecular processes. Today, CT and US and to a large degree MR imaging are used primarily for anatomic imaging purposes, even though there is the capability for all three of these modalities to be used, to varying degrees, for physiologic assessments. MR imaging has the capability to make some molecular imaging assessments. PET and optical imaging, on the other hand, provide less anatomic information and are primarily molecular and, to a lesser degree, physiologic imaging techniques.