We are in the midst of major advances in medical imaging, converting static pre sentation of anatomic information into near real-time interactive imaging and displays capable of depicting both structure and function. This will have pro found impact on diagnosis and image-guided therapies. These advances have been most notable in the modalities of computed tomog raphy and magnetic resonance. These technologies have become capable of ac quiring volumetric images in short periods of time. Speed gains in MRI were very significant in the early 1990s with the development of clinically usable pulse se quences for gradient-recalled and echo-planar imaging. It appears that further speed gains in MRI will be difficult to achieve. The development of spiral CT has ushered in an era in which major speed gains in CT are also possible. This has enabled creation of new types of applica tions such as CT angiography, which has already come to replace catheter angio graphy at many medical centers throughout the world. We are very pleased that the results from industrial and academic laboratories have been transferred to the bedside to improve patient care at a speed that may be faster than in any other area of medicine. Concurrent with advances in CT technology there have been dramatic strides in the performance characteristics and costs of computer hardware and software.