Variable-mode helical CT: imaging protocols.

Abstract

Helical CT provides a rapidly acquired, accurately registered, two-dimensional data set during the phase of maximum vascular and parenchymal enhancement. The z-axis can be covered by using either a single acquisition, single breath-hold technique or by using multiple helical groups with intergroup delays for the patient's breathing. The latter approach, called variable-mode helical CT, allows large z-axis coverage of more than one anatomic region during injection of a single bolus of contrast material. We discuss helical scanning protocols, both single-acquisition and variable-mode, that we have developed for detection of disease involving major blood vessels (pulmonary arteries and aorta), perivascular tissue planes (neck, thorax, and pelvis), and abdominal viscera (liver, pancreas, and kidneys).