The field of medical imaging is undergoing a radical shift, from subjective interpretation to quantitative analysis and measurement. This transformation is well established in the clinical trials arena and is beginning to enter the diagnostic field as well. This article will consider the implications of this change in terms of instrumentation, procedure, and analysis. It will include a brief review of current imaging practices and standards, focusing primarily on the clinical trials arena, and will examine in detail the acquisition and analysis techniques that will be required to successfully complete the transition from qualitative to quantitative imaging.