For all that new non-X-ray technologies such as MR and ultrasound and its various manifestations have made an enormous impact in recent years on the practice of medical imaging, the use of X-rays and X-ray contrast-enhancing agents has retained an important position at the heart of the process. Indeed, with its frequent requirements for high total dose regimes, CT has increased the use of contrast agents. Even helical/spiral CT which, it was initially argued, should reduce contrast as well as radiation loads, may actually require just as much or more of both because of the potential it offers...